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Abstract This article deﬁnes the present moment in the anthropology of embodied human communication as a moment of possible fusion between (a) the new conception of the living human body emerging in biology, cognitive science and neuroscience, and sociology and anthropology and (b) the advanced methodology and research on social interaction in the “interactionist” tradition, which is reinterpreted here as a study of socialized practices for interacting in, and inhabiting, the world with others. A growing number of studies of interaction are now focused on “multimodal” communication in complex material settings. The convergence of research programs is illustrated here by sociological research on dance and sports, by a practice-based approach to gesture, and by a selective overview of recent studies of multimodality. Particular attention is given to two inﬂuential theoretical programs, one by E. Hutchins and the other by C. Goodwin. 419 INTRODUCTION In the past few decades, the conventional conception of nonverbal communication has become unmoored and is rapidly losing its grip on research and theory, increasingly so as more scholars across disciplines take a serious and sustained interest in the living human body and its being in the world. The old model had conceived of human senses and body parts (voice, eyes, hands, etc.) as “channels” through which “messages” travel. Sender and receiver are construed as mind or brains, as central processing units which encode and decode immaterial meanings conveyed by material signs. The body in this model was but an instrument at the service of some central, meaninggenerating internal “system,” recruited solely for the production of forms and separated from its other skilled and meaningful doings in the everyday world. Although the sender-receiver model has never gained much overt traction in anthropology (which has tended to ﬁnd communicative forms within rich ﬁelds of material culture and activity), a notion of the body as passive bearer of coded cultural messages has nevertheless been a tacit foundation of much work (e.g., Douglas 1970). Against the sender-receiver paradigm, beginning in the 1950s, but gaining momentum in the 1970s, an increasing number of researchers across disciplines, working from ﬁlm and video recordings of everyday interactions, have shown that communicative actions accrue meaning as they emerge in the moment-by-moment interaction of copresent parties. Thus, rather than the encoded content of an individual mind, meaning is a relationship between form and context, with context as an ongoing product of sequential and complementary action. Research in the interactionist tradition of Mead (1934), Bateson (1971), and Goffman (1963, 1971), notably context analysis (Kendon 1990, Scheﬂen 1973) and conversation analysis (Sacks et al. 1974), has been gaining increasing inﬂuence and is now, in many ﬁelds, the prevailing methodology offering the largest body of empirical ﬁndings. But new impulses for reframing embodied communication also come from a variety of other sources, few of which have so far been taken up, let alone absorbed, in interaction research. These sources are found in the wake of the so-called body and practice turns in sociology, anthropology, and linguistics (Schatzki et al. 2001); in the revival of phenomenology, including the “anthropology of experience” (Csordas 1990, Jackson 1989); in the happy marriage of biology, neuroscience, and phenomenology formed in various “neurophenomenological” programs (Fuchs & de Jaeger 2009, Stewart et al. 2010, Ziemke et al. 2007); and in the fusing of ecology and phenomenology in an anthropology grounded in human “dwelling” (Ingold 2000, 2011). This article deﬁnes the present moment in the anthropology of embodied communication as a moment of possible fusion between the new conception of the living human body emerging in biology, cognitive and neuroscience, and sociology and anthropology, on the one hand, and the advanced methodology and research on social interaction in the “interactionist” tradition, on the other, which is understood here as a study of socialized practices for interacting, understanding, and inhabiting the world with others. Although interaction research began with a focus on a single modality, or a small set thereof (speech, gaze, gesture, etc.), over the past several years, “multimodal interaction” has become a programmatic term, and a growing number of studies are now devoted to the analysis of communication that is embedded in, and incorporates, material settings rich in artifacts, technologies, and external representations (Streeck et al. 2011). This research program is illustrated by sociological research on dance and sports; a practicebased approach to gesture; an overview of the development of the ﬁeld; and an appreciation of two inﬂuential theoretical programs, one by E
. Hutchins and the other by C. Goodwin. Both Hutchins and Goodwin emphasize that semantic and pragmatic meanings of communicative acts are coconstructed in the interaction of the parties involved. As conversation analysts have argued (Sacks et al. 1974), the recipient’s responsive act ultimately determines the signiﬁcance of the turn 420 Streeck at talk. This feature is given only scant attention in this review, which focuses on the role of the living body in the production of communicative acts. COGNITIVE BIOLOGY OF BODY MOTION Central to the new, antidualist conception of embodiment is recognition of the fact that every living movement has a cognitive component (Sheets-Johnstone 2012), a perspective emerging from the conception of life and cognition by Maturana & Varela (1980) as “autopoiesis” or self-organization (see also Varela et al. 1991). “There is a basic formal organization of life, and its paradigm and minimal case is... the single cell. A single-cell organism is a self-making... being... In self-production, a cell continuously produces itself as a spatially bounded system, distinct from its medium or milieu” (Thompson 2007, p. 92). Motion is a fundamental mechanism of an organism’s self-making within a milieu. By moving its body or a body part, it responds to an environmental cue and picks out its signiﬁcance or “value” within the environment (Ziemke et al. 2007). By habitualizing couplings between cues and motions, organisms create an Umwelt (von Uexk¨ull 1957). This process has been called “sensemaking”: “An autopoietic system always has to make sense of the world so as to remain viable. Sense-making changes the physicochemical world into an environment of signiﬁcance and valence, creating an Umwelt for the system” (Thompson 2007, pp. 146–47). Cognition is not a separate process “in the mind” or the brain; “cognition is embodied action” (De Jaegher & Di Paolo 2007, p. 486). From these actions, other organisms build their Umwelt, all becoming implicated in the emergence of communicative webs and social organization. The organic identity of cognition and motion is illustrated by the brain. Only organisms that possess motricity have brains. The sea anemone, whose life cycle comprises a sedentary (plant-like) and mobile (animal-like) stage, grows a brain during the latter and reabsorbs it in the former. The original function of the brain, then, is to allow mobile organisms to anticipate the consequences of their movements in a medium or Umwelt. Cognitive scientists since William James have therefore suggested that thinking and other “high-level” activities in the human brain have ultimately evolved from motor control and that thinking is “internalized motion” (Llinas 2002). Research has shown that humans perceive all self-propelling movements by living organisms as intentional (Brentano 1995), that is, as being oriented to an object and toward a goal. In other words, identifying living motion with cognition is also our “natural attitude” (Schutz 1967). However, kinesis is impossible without kinesthesia (Sheets-Johnstone 2010). Animals sense their motions through internal receptors (“muscle sense”). In his study of the “haptic system,” the perceptual system through which grasping hands experience the world, Gibson (1966) laid out that our tacit bodily knowledge of the world around us consists of proprioceptive—“felt”— patterns of actions such as grasping. That kinesthesia is an indispensable component of intelligent motion poses a conundrum for theory and research on intercorporeal communication, given that our kinesthetic experiences do not appear to be accessible to others. The requirement, so emphatically and convincingly stated especially by conversation analysts (Sacks et al. 1974), that only those dimensions of action that are publicly available can ﬁgure in the interactants’ mutual sensemaking, thus, excludes kinesthetic phenomena. However, the fact that the body motions of others are usually only visually available to us (disregarding moments of touch) does not mean that we perceive them with only our eyes. One of the breakthroughs in recent neuroscience has been the discovery that our own motor-control system is activated whenever we see others move in familiar ways ( Jeannerod 2006). Our motor system (i.e., the neural networks operations of the motor and premotor cortex and their operations) and our perceptual systems overlap; consequently, we recognize and understand the actions that www.annualreviews.org • Embodiment in Human Communication 421 we know how to perform. We “emulate” them covertly as we are seeing them (W
olpert & Miall 1996) and thus are able to anticipate their trajectories before they have taken their full course. A popular ﬁnding related to this research has been the discovery of mirror neurons in rhesus monkeys, which ﬁre not only when the animal executes a grasping motion, but also when it observes one. Mirror neurons have become an icon for the hope to ﬁnd a “brain organ” that produces intersubjectivity, i.e., the ability to understand other minds. But, as Jeannerod (2006) has pointed out, mirror neurons are not perceptual neurons at all, and they do not produce imitation (as the term “mirror” suggests). Rather, they constitute a “vocabulary” of actions that an individual knows how to perform and has practiced; they ﬁre whenever an instance of such an action is being observed. Their operation depends, as it were, on participation in a shared culture. In addition, the body motions that we are most likely to recognize among random visual noise are our own, the only ones that we cannot possibly see as we perform them (Loula et al. 2005). What our bodies know how to do is also what they are able to see. All these cognitive-communicative processes are “autonomic”; they occur outside our realm of attention, and focusing our consciousness on them usually disrupts them. Neuroscience thus has given us a view of the body in which autonomic “body-to-body” understanding is possible to the extent to which our bodies share sufﬁciently familiar patterns of action. It has thereby opened up the body to other bodies, to the world, and to culture. In doing so, it has transformed the body from an anatomical structure and instrument of the mind into a living body, the “Leib” of phenomenology (Husserl 2012), a dweller and comaker of life-worlds. THE LIVING BODY OF PHENOMENOLOGY The congruence of “embodied” neuroscience with phenomenologists’ view of the human body’s being in the world is most evident in the work of Merleau-Ponty, who wrote that “the body is our vehicle of being in the world, and having a body is, for a living creature, to be involved in a deﬁnite environment” (Merleau-Ponty 1962, p. 82). The living body is constituted in part by its relation to things. “To move one’s body is to aim at things through it; it is to allow oneself to respond to their call” (p. 138), and actions that we routinely perform (habits) “incorporate their instruments into themselves and make them play a part in the original structure of my own body” (p. 91). But action also always includes a measure of “groping” (tˆatonnage) (Leroi-Gourhan 1993), a reaching for “maximal grip,” an articulation of the sedimented habit with the contingencies of the situation, a tendency on the part of the body “to reﬁne its responses so as to bring the current situation closer to an optimal gestalt” (Dreyfus 2002, p. 367). As the active body acquires skills, those skills are stored, not as representations in the mind, but as dispositions to respond to the solicitations of the situation. The living body is constituted not only by its incorporation of things, but also by its incorporation of other bodies. Merleau-Ponty called this relation “carnal intersubjectivity” and “intercorporeality” (intercorpor´eit´e) (MerleauPonty 1962) and illustrated it by the handshake: [W]hen I shake his hand... [the other man’s] hand is substituted for my left hand, and my body annexes the body of another person... My two hands “coexist” or are “compresent” because they are one single body’s hands. The other person appears through an extension of that compresence; he and I are like organs of one single intercorporeality. (Merleau-Ponty 1962, p. 168) This compresence constitutes one foundation of our bodies’ ability to understand each other, “the reason the compresence of my ‘consciousness’ and my ‘body’ is prolonged into the compresence of my self and the other person” (Merleau-Ponty 1962, p. 175). 422 Streeck The handshake is an example of a “face-engagement” (Goffman 1971), constituted by mutual attention. Although this is the mode of social engagement in which human life, sociality, and intersubjectivity begin, it is only one primordial form of social engagement; the other is
constituted by joint attention to and engagement with the world of things and begins around the fourth month of life (Trevarthen 1998). Intercorporeality in this sense is a relationship among “incarnate minds which through their bodies belong to the same world” (Merleau-Ponty 1962, p. 172; also see Meyer et al. 2015). This dimension of our being is central to Heidegger’s phenomenology (Heidegger 1926; also see Dreyfus 1991). According to Gordon (2014, p. 34), Heidegger proposed that philosophy should take as its cue our everyday commerce with worldly things. When I wield a hammer, my knowledge of that hammer is not primarily a matter of how it is represented or conceived; it is an implicit know-how that animates my action and embraces its elements all at once: the weight of the tool, the heft of the wood, my care in the work, and so forth. This everyday kind of purposeful involvement motivates a general picture of the human being as already immersed in its world. Heidegger took the term Dasein, “being there” or “being-in-the-world” (Dreyfus 1991), to refer to the human being who is “always already” immersed in the world of things through “mindless” (representation-less) absorbed coping or “dwelling.” We “dwell in” or “inhabit” the places where we, the tools that we use, and the speaking routines that we perform all are. When we inhabit something it is no longer an object for us but becomes part of us and pervades our relation to other objects in the world... Dwelling is Dasein’s basic way of being-in-the-world. The relation between me and what I inhabit cannot be understood on the model of the relation between subject and object. (Dreyfus 1991, p. 45) Our basic mode of being-in-the-world is not constituted by the unoccupied face-to-face relation but by “Mitsein” (being-with) or “Miteinander” (with), which is “equal behavior towards things” (Heidegger 1928/1929). Being-with is not constituted by mutual understanding (“erfassen,” grasping). Mutual understanding is founded in being with one another. Dasein must already be transparent (“offenbar,” disclosed) for Dasein for mutual understanding to be possible. Being transparent for one another appears in such circumstances as two wanderers being caught by the view. (Heidegger 1928/1929, pp. 87–88; translation by J. Streeck) THE “DWELLING PERSPECTIVE” Ingold has grounded a far-ranging anthropological research agenda in the phenomenology of being-in-the-world, integrating it with Gibson’s (1986) ecological psychology and Marx’s (1973) early historical materialism with its focus on the subjective side of praxis. Ingold (2011, p. 11) is concerned to “unite the approaches of phenomenology and ecology within a single paradigm.” From his “dwelling perspective,” Ingold (2011, p. 10) notes, “the forms humans build, whether in the imagination or on the ground [or in gesture and speech] arise within the currents of their involved activity, in the speciﬁc relational contexts of their practical engagement with their surroundings.” Situating the human body, the subject of perception and action, within its “involvement whole” and “on the ground,” Ingold (2004) analyzes culture members’ perceptions and cognition in a “horizontal” perspective along their “paths of observation” as a “gathering” and “lateral integration” www.annualreviews.org • Embodiment in Human Communication 423 of meanings, thereby countering the traditional account of culture as an imposition of meaning and form onto inherently meaningless media and substrates. Ingold’s decisive move has been to recognize the continuity of world-making (niche-building) and meaning-making across all forms of organic life, notwithstanding the distinct human ability to “rachet up,” reﬁne, and reanalyze shared skills, forms, stories, and practices—culture—from generation to generation. Ingold does not study videotapes of human communication, but he gives researchers in that ﬁeld a rich and coherent heuristic for coming to terms with the moment-to-moment activities—the dwelling—in which all embodied communication takes place and from which it takes its material. THE BODY’S HABITUS AND PRACTICES An anthropological text that has been reanimated in the discourse about the body is Techniques du corps. In this text, Mauss (1973, p. 70) describes “the ways in which from society to society men know how to use their bodies.” For example, “the positions of the arms and hands while walking form
a social idiosyncrasy, they are not simply a product of some purely individual, almost completely psychical arrangements and mechanisms” (p. 72). Mauss introduced the term “habitus” to refer to these social idiosyncrasies of the moving body, translating the Aristotelian notion of hexis, “acquired ability” and “faculty.” In bodily habits, Mauss (1973, p. 73) saw “the techniques and work of collective and individual reason” (emphasis added). Bourdieu (1977, 1990), with whom the term is usually associated and who much inspired the “practice turn,” deﬁned habitus as “a system of durable, transposable dispositions”: To understand habitus one has to situate oneself within “real activity as such,” that is, in the practical relation to the world, the preoccupied, active presence in the world through which the world imposes its presence, with its urgencies, its things to be done and said, things made to be said, which directly govern words and deeds without ever unfolding as a spectacle. (Bourdieu 1990, p. 52) The habitus, a product of history, produces individual and collective practices—more history—in accordance with the schemes generated by history. It ensures the active presence of past experiences, which, deposited in each organism in the form of schemes of perception, thought and action, tend to guarantee the “correctness” of practices and their constancy over time. (p. 54) Habitus constructs the world by a certain way of orienting itself towards it, of bringing to bear on it an attention which, like that of a jumper preparing to jump, is an active, constructive bodily tension towards the imminent forthcoming. (p. 144) As these quotes demonstrate, Bourdieu’s concern was to discern sedimented history in the habitus of individuals, most clearly felt in the forward-looking tensions of the body toward its projects in the world. However, Bourdieu gave little attention to the spontaneity and creativity of action ( Joas 1996), to its potential to transcend and remake sedimented practices (Noland 2009), or to the ways in which individuals acquire the speciﬁc subjectivity—the embodied self—that is associated with a habitus (but see Wacquant 2004). INTERCORPOREALITY IN DANCE AND SPORTS Of particular interest in the present context is sociological and linguistic research on the selfmaking of bodies in the practice ﬁelds of dance and sports (Alkemeyer et al. 2009, Haller 2009, 424 Streeck Markula 2006) as well as the temporalities of language and body motion in instructional practice and their integration (Keevalik 2015). Dancing and sporting bodies are constituted by their heightened and practiced abilities for tacit intercorporeal coordination and action. Dance allows sociologists to investigate how dynamic, yet recurrent and intelligible, behavioral orders are established, known, and sustained under contingent conditions. Argentine tango dancers, for example, seek to reach, through sequences of steps that are both routine and improvised, the exalted moment when two bodies move as one “four-legged animal” (Elsner 2000). The order of steps in a basic sequence is not ﬁxed; each member of the dancing couple must at every step anticipate what the other will do next, which is made possible through haptic communication via their torsos, arms, and hands. Movement practices such as classical ballet and taiji also bring to the fore cultural values and conceptions of the body. The classical corps de ballet is an anatomical body, trained to maximize degrees of freedom and produce movements that create “the illusion... of the dancer being light as a feather in movement” (Mitchell 2013, p. 4). The body of taiji, in contrast, is moved by the ﬂow of chi, life energy, and the goal of practice is to move so that energy from the body’s center can ﬂow into these motions, and to ease one’s thoughts and feelings into them so that the mindful body will be enabled to spontaneously and prudently respond to the intercorporeal contingencies of any situation. (Mitchell 2013, pp. 4, 6) Presently, millions of people in the industrialized world are attempting to transform their bodily identity by acquiring the movement idiom, habitus, and “carnal intersubjectivity” of Latin salsa, merengue, and tango. Key experiences in the acquisition of movement genres such as dance (particularly ballet) and sports are the incessant confrontations with the obstinacy or recalcitrance of the body, the experience that movement possibilities are constrained by incorporated normative culture. Sedimentation enables, but also limits, spontaneity. Yet it is also a common experience in this context that
the body is capable of performing autonomic and adaptive motions that transcend and innovate habitualized patterns. The very enactment of a practice by an obstinate body entails the possibility of resistance, criticism, and cultural change (Alkemeyer 2004, Noland 2009). Team sports such as volleyball are activities that require “hypercooperativity” (Meyer & von Wedelstaedt 2015), for example, when volleyball players take ﬂight in unison to block a ball, anticipating its trajectory from the preparatory moves of the opponent. In such moments a “wesubject” is brought into being (Schutz 1982). Sports therefore presents... a litmus test for existing theoretical models of communication, sociality and interaction, since it reveals features of social life that are foundational even though they have been systematically neglected by all social theories that took social spaces that... are relieved of practical constraints... as their starting point. Many aspects that are present in sports, however, equally apply to other activities that occur under time pressure and at great social speed, through the coordination of bodies and things. (Meyer & von Wedelstaedt 2015, p. 11) Elias (2009, p. 124) has noted that the social sciences traditionally have considered the state of being at rest the “normal state of affairs [and]... movement a deviation”; he recommended against abstracting away from the in-motion nature of social phenomena. Indeed, “the sporting environment—both physical and social—is in the main perceived by the participants, not from a static position, but rather from a moving vantage point” (Hockey & Collinson 2007). During dance instruction, the different temporalities of speech and moving bodies must be aligned (Keevalik 2015). Another advantage many researchers of dance and sports have is that they are also www.annualreviews.org • Embodiment in Human Communication 425 professional practitioners of these ﬁelds, and close conscious attention to kinesthetic experience is part of their habitus; the viability of a discourse of kinesthesia is familiar to them from training and practice. This is a vantage point that interaction researchers often lack: Although we are also practitioners of the phenomena that we study, we inevitably produce and experience these in the “natural attitude” (Schutz 1932): We have not been trained to interact, and our only conscious access to the phenomena in question is through videotapes, which ﬂatten out interpersonal perception and reduce it to its audible and visible dimensions. GESTURE PRACTICES In the new ﬁeld of gesture studies that emerged in the 1990s, inspired especially by the observational, “naturalistic” work of Kendon (2004) and the experimental psycholinguistic research of McNeill (1992, 2005), it was common to regard gestures either as utterance components (Kendon) or as external representations of “thinking-for-speaking” (Slobin et al. 1987), of the “holistic-synthetic” dimension of thought that is articulated with the “analytic” mode during speech (McNeill). Streeck (2009b) breaks with these intertwined traditions and approaches gestures of the hand as they emerge from, and mediate, collaborative physical action. Building on work by Kendon (2004) and Goodwin (2000), Streeck (2009b) proposes a view of gesture as craft, a distinct yet heterogeneous family of manual sensemaking practices that abstract communicative forms from everyday actions and construe experience in terms of actions of the hands. To understand how hand gestures work, we must begin with an appreciation of the kinds of organs that human hands are. Originating as organs of locomotion, as ﬁns that became feet, hands eventually acquired unique sensory abilities and precision grip and became organs for toolmaking or productive labor (Streeck 2009b, ch. 3). The most characteristic movement of the human life-form is the “gesture of making” (Flusser 2014), in which the two hands come together in complementary cooperation, making something out of something, attended by the eyes. Through the same processes, human hands have evolved into our most sophisticated organ for environmental cognition, i.e., for feeling, assessing, and comparing textures, consistencies, shapes, and the affordances of things. Gesture is a symbolic practice that draws upon this tacit knowledge: It makes distinctly manual patterns of experience, habits, and skills—schemata—available to the sensemaking person. It is possible to discern different ecologies in which gesture practices partake, i.e., how they differentially contribute to the communicative situation. This is, at one level, an issue of perception: Are gestures perceived as “free-standing” ﬁgures, or in relation to an environmental feature or ground? Does a gesture depict a distant object that is being discussed, or, instead
, does it display the “illocutionary act” (Austin 1962) that the speaker is performing? The “intentional arcs” of gestures point in different directions, each arc implying a different role for the gesture within the moment of sensemaking. Streeck (2009b) distinguishes six “ecologies of gesture”: 1. Hand gestures can investigate the world within reach and disclose and elaborate its features and signiﬁcances by active exploration and visible manipulation (“environmentally coupled gestures”) (Goodwin 2007a). 2. Gestures can select and elaborate features and signiﬁcances of the “world in sight” and orient the interactants in relation to them (pointing toward and tracing visual phenomena in the distance). 3. Gestures can evoke phenomena that are not present or model imaginary and abstract worlds (depictive gestures). 4. Gestures can conceive thematic content by casting it in terms of postures and actions of the hands (conceptual gestures). 426 Streeck 5. Gestures can embody and display aspects of a communicative act, for example, a speech act that is concurrently performed (pleading, praying, etc.). 6. Gestures can regulate the actions of others. These categories, which may not accommodate ritual gestures that solicit or manifest deities or spirit forces or pay tribute to them, are not disjunct; a pointing gesture by deﬁnition regulates the action of another by suggesting a shift or focus of gaze. A single gesture can also do different things at the same time or condense multiple signiﬁcances into a single form. Importantly, different modes of gesticulation involve different degrees of attentiveness and awareness. Pointing gestures and depictions are deliberately made and given their maker’s and addressee’s visual attention (Streeck 1993). By contrast, conceptual and “pragmatic” gestures are commonly not oriented to by the participants, remaining at the periphery of the attentional ﬁeld, where they spectacularly display the human body’s autonomic sensemaking abilities. In this mode of gesturing, hands spontaneously give form, say, to abstract notions of community, to the feeling of comfort, or to the imminent beginning of storytelling (Streeck 2009b, ch. 8), unpredictably shifting their “intentional arc” from one phrase to the next. As such, this mode is full of both conventional forms and personal idiosyncrasies, forever demonstrating that the “energeia” (Humboldt 1988) of language-making, or communicative action, can never be fully subsumed under the “grammar” of the forms that it secretes. For each of the orientations to the situation, distinct gesture practices have evolved. The methods people use to depict or refer to objects include drawing using an index ﬁnger, molding, and “modeling” (Kendon 2004, M¨uller 1998; see also Enﬁeld 2003, 2005), but the preference seems to be for gestural “handlings,” schematic versions of movements by which we handle these objects in everyday life. Thus, in the depiction of objects via gesture, we rely on a common ground of familiar “couplings” between motor actions and the kinds of things being depicted. Streeck noted that several of the basic methods for depiction correspond to a fundamental mode of being of the human hand, some general capacity in which the hands engage with the world: in the service of transportation, for example, moving things from one place to another... As users of things, hands know each thing by its affordance. Hands also act in the capacities of explorer and disassembler and, supremely, as maker and molder of things. These capacities are engaged in abstracted form in... gestural depiction... Gestural depiction is grounded, then, not in visual resemblance, but in the everyday interpenetrations of actions and things. (Streeck 2008, p. 298) Investigating the emerging gestures of very young children, Andr´en (2010) has shown how distinctly communicative gestures are separate from “instrumental” physical acts such as reaching, taking, and giving. The “action gestalt” of early communicative gestures emerges through the “freezing” and separation of some stage in the excursion and behavior of the hand during a manipulatory act such as taking hold of an object within reach. The action unfolds as the hand moves away from the body toward the object, forming a prehensile posture in the process, grasping and lifting the object, holding and perhaps manipulating it, setting it down, and retracting the hand. Each of these phases can give rise to a gesture, which is “immediately” transparent in the context because it is perceived as an inherently meaningful phase of an inherently meaningful act. Andr´en offers
a ﬁne-grained set of distinctions to show how gestures emerge from object-related and interpersonal actions, becoming visual rather than haptic acts, separated from the model by degrees of communicative explicitness and semiotic complexity. Similar methods for abstracting meaningful enactive schemata from everyday actions with things appear to pervade developing “home sign” systems (Haviland 2013) and sign languages (Kendon 2009). Whenever hands make www.annualreviews.org • Embodiment in Human Communication 427 meaning through gesture, some reconﬁguration of sensations seems to be involved. Although all hand gestures are visible actions, the sensory experiences that they otherwise involve and draw upon are diverse: tactile, haptic, digital (i.e., using an index ﬁnger as “antenna”) (Napier 1980; cf. Deleuze 2003). STUDIES OF EMBODIED AND MULTIMODAL INTERACTION Beginning in the 1950s and gaining momentum in the 1970s with the advent of video technology, a large ﬁeld of study of the moment-by-moment production and organization of social interaction has grown, the seed of which was The Natural History of an Interview project in Palo Alto, California (Leeds-Hurwitz 1987, Lipset 1980). Using ﬁlmed records, researchers, including Gregory Bateson and Ray Birdwhistell, set out to study for the ﬁrst time how interacting dyads or groups sustain themselves as self-regulating systems, by which bodily behaviors interaction participants “frame” the “working consensus” (Goffman 1963) of their encounter, and how behavioral forms become intelligible within behavioral contexts and sequences of symmetrical and complementary action (Bateson 1958, 1971, 1972). An equally important, yet often unacknowledged, inspiration for this research is Mead’s (1934) work, especially his scenario of a “conversation of gestures,” of sequential, complementary interactions in which signiﬁcant gestures and symbols emerge. The “interactionist tradition” comprises both context analysis (Kendon 1990, Scheﬂen 1973) and conversation analysis (Sacks et al. 1974; Streeck 2009b, ch. 2; Streeck et al. 2011; for an account of the development of the ﬁeld and its methodology, see Kendon 1990; for a comprehensive overview of conversation analytic research on bodily action, see Heath & Luff 2012; for a review of Kendon’s work, see Streeck 2007; for a broad range of approaches and themes, see M¨uller et al. 2013). Bateson (1956) conceived of context as “framing,” a logical typing of communication, signaled and sustained by metacommunication: During animal interactions, through signals such as “play faces,” otherwise antagonistic acts, e.g., bites, are recontextualized as play. Bateson’s conception informed Scheﬂen’s (1964) groundbreaking studies of posture and posture conﬁgurations as embodied contexts in therapeutic interaction as well as the methodology for context analysis that he developed (Scheﬂen 1973). Bateson’s work also inﬂuenced Kendon’s (1990) “dynamic” account of the moment-by-moment interaction in which interactional formations are assembled, sustained, tuned, and dismantled. Numerous studies have since investigated the spatial organization of social encounters (Hausendorf et al. 2013, Mondada 2009), including the coordinations required, both within each party and between them, of body orientation, gaze, and speech in both stationary and mobile ensembles (Haddington et al. 2013, Mondada 2012). Further research has explored how these participation frameworks are being reconﬁgured by new communication technologies (Button 1993, Heath & Luff 1993) and how the physical arrangement of the setting mediates and constrains talk and interaction (Lebaron & Streeck 1997). Other research has investigated how spatial posture, positioning, and orientation embody affect and stances taken toward the other’s act (Goodwin 2007b, Goodwin et al. 2012) and how postures operate within the moment-by-moment organization of the participation framework (Goodwin & Goodwin 1992), including the distribution of participation roles and rights. Recently, research has begun to investigate the zone of immediate or “haptic sociality” to consider the ways in which families touch and hug and parental arms and hands scaffold and constrain the body motions of their children (Goodwin 2015, Tulbert & Goodwin 2011). Working with the deaf-blind community in Seattle, Washington, Edwards (2012) has studied how speakers of deaf sign language who are losing their
eyesight are developing modes of tactile and haptic sociality and communication. Research on bodily components of the organization of talk in interaction initially focused (a) on gaze (Kendon 1967), i.e., how the sequencing of mutual gaze operates in the turn-by-turn 428 Streeck organization of talk (Goodwin 1979, 1981; Heath 1982); (b) on the temporal and semantic coordination of gestures and speech (Kendon 1972, 1983); and (c) on the role of gaze and speech in directing attention to gestures (Goodwin 1986, Streeck 1993) and the role of gestures in directing gaze (Heath 1986). Through gaze and facial actions, speakers and listeners can negotiate the dynamic development of a turn at talk (Goodwin 1979, Iwasaki 2011). Rossano (2012) showed that the requirements for mutual gaze are contingent on the course of action or sequence type under way. Only recently have interactionist researchers begun to investigate the display and management of affect in conversational interaction (Per¨akyl¨a & Sorjonen 2012). A signiﬁcant ﬁnding from all this research is that gestures, similar to other communicative motions of body parts, very often “project ahead”: They foreshadow what is about to be said or done (Schegloff 1984; Streeck 1995, 2009a), and their signiﬁcance lies in preparing the next moment (McDermott et al. 1978). These studies concern interaction in the face-to-face mode. Mitsein, shared engagement with the world at hand, ﬁrst came into view in studies of deixis and pointing (Kita 2003), of the ways in which the “deictic system” of a language cooperates with the deictic system (or set of deictic practices) of gesture in structuring a situated deictic ﬁeld (Hanks 2005). Studies include research on the signiﬁcance of choices among body parts (Enﬁeld 2001, Wilkins 2003) and hand shape (Kendon & Versante 2003) in pointing and of the impact of the conceptualization of space in a language community (absolute or relative) on the practices of pointing (Haviland 1993, 2003; Levinson & Wilkins 2006). In a similar vein, Cooperrider & Nu˜nez (2009) and Nu˜nez & Sweetser (2006) have investigated how spatial “conceptual metaphors” of time reverberate in gestures referring to time. Reaching out into the “manipulatory zone” (Mead 1932), i.e., the world at hand, interactants in work settings may ﬁnd inscriptions and the means to make them. Although these inscriptions afford the recording of meaning for the longer term, they often require annotation and interpretation by embodied (gestural) acts (Streeck & Kallmeyer 2001): Two-dimensional diagrams and blueprints often become imbued with a third and fourth dimension (volume and time). Gestures are also integral to the collaborative production of imagination, for example, in the work of designers and architects (Murphy 2005, 2011). Things at hand are recruited—exhapted—for purposes beyond their indigenous affordances; they are subsequently arranged and manipulated in ways that give form to social meanings (Streeck 1996). Increasingly, then, interaction researchers are coming to terms with the whole complexity of interaction, cooperation, and sensemaking in the human-made world that we inhabit and of the divergent temporalities of the systems involved (Deppermann & G¨unthner 2015). Much of the research on “multimodal interaction” in recent years has been conducted in technology-rich workplaces, including subway and airport control rooms (Goodwin & Goodwin 1996, Heath & Luff 1996), cars and cockpits (Mondada 2012, Nevile 2004), car-repair shops (Streeck 2002), and surgerytheaters(Mondada2011).Inthesesettings,bodilyactsofcommunicationoftenincorporate tools and electronic media, for example, when physicians during laparoscopic surgery perform communicative gestures with their instruments while observing each other’s actions on a monitor (Koschmann et al. 2007, Zemel et al. 2001). Such settings reconﬁgure the perceptual and enactive conditions for interaction and sensemaking, requiring new adaptations and spurring the rapid evolution of new practices (Keating & Sunakawa 2011). EMERGING THEORIES Hutchins (1995, 2006) approaches interaction from a “distributed cognition perspective,” according
to which the socially organized cognitive system, not the individual, is the unit of analysis for the study of cognitive activity. This system includes not only a network of actors and the media of communication available to them, but also tools and the historically constituted skills coupled www.annualreviews.org • Embodiment in Human Communication 429 with them, the spatial arrangements that they inhabit, media that can store information, and so on, which together form a “cognitive ecology.” Hutchins is particularly interested in the affordances of cognitive tools involved, and of the embodied human agent, for holding, propelling, and computing information and in the interfaces among them. Analyzing the collaborative construction of multimodal utterances in an explanation given by an airline pilot in a moment of crisis, Hutchins & Palen (1997) observe that “the meaning of the explanation is carried in the coordination among the spatial organization of specialized artifacts, the positioning of gestures with respect to those artifacts, and the words that are spoken” (Hutchins & Palen 1997, p. 23; see also Hutchins & Nomura 2011). Hand gestures are especially ﬂexible cognitive artifacts. For example, the gestures superimposed on the space of the [fuel] panel can be read as meaningful actions and courses of action on the fuel panel itself, or they can be seen as events in the fuel system. To see the gestures as actions on the panel, one must see the panel as a panel. To see the gestures as representations of events in the fuel system, the panel must be seen as the system that it represents. (Hutchins & Palen 1997, p. 37) In another context, where scientists attempt to formulate theory, “representational gestures serve to reference and animate portions of existing material structure such as models, diagrams, and graphs” (Becvar et al. 2005, p. 89) and instantiate “essential spatiodynamic features [e.g., of molecules]... not effectively conveyed in other modalities” (p. 89). Hand gestures can also serve as “material anchors” (Hutchins 2005), giving stable sensate forms to emergent conceptualizations (cf. Freedman 1977). In much of his work, Hutchins has assumed “the separation of dedicated modalities for experiencing [and acting in] the world and for communicating about it” (Hutchins & Johnson 2009, p. 527) and the existence of a “dedicated communication channel that is separated from the other sensorimotor channels” (p. 530). But Hutchins & Johnson (2009) realized that, to explain how “the capacity for representation” (p. 523) emerges, what is needed is a scenario “in which signals [inhabit] the same domain of sensorimotor experience as other events and objects in the world” (p. 532), because “iconic signs” develop through the abstraction of sensorimotor patterns from sensorimotor action. Hutchins & Johnson (2009) found such a scenario in the interactions of bonobos, which “spontaneously produce embodied forms that have some, but not all, of the features of language” (p. 534). Gestures emerge when infants abstract stages of participation in familiar interaction patterns—for example, being picked up to be carried—and present them to their mothers visually. Mothers and experienced infants come together for the carry activity in a very ﬂuid way... Mothers often sweep up infants and move off while looking at their destination... The infant simultaneously moves its body and hands in ways that ﬁt and take advantage of the mother’s motions. Mother and infant just come at one another, interdigitating (grab, climb on, lift, etc.) mainly by feel. Bonobo mothers experience most carries as tactile and proprioceptive events rather than as visual events... The infant’s gesture is made available to the mother as a visual experience, yet it seems to refer to an activity that consists primarily of tactile, motor, and proprioceptive experience. (Hutchins & Johnson 2009, pp. 535–36) This ﬁnding parallels Streeck’s (2009b, 2013) suggestion that the capacity for manual gesture in humans is abstracted from sensorimotor (haptic) experience and action. Instrumental and communicative action overlap and do not constitute separate “modules.” The bodily actions of others can be transparently meaningful for us without thereby becoming signs; signs originate when actions are performed speciﬁcally for communicative purposes. 430 Streeck Hutchins & Johnson (2009, p. 536) further observe that “the primary form of coordination in this activity is the production of complementary rather than matching (imitation) behavior... Actions that ‘ﬁt’ the actions of the other are favored. Actions that do not ﬁt the actions of the
other are dissipated.” These abstracted gestures can become common currency in a group. “Putting signals into the world of action... creates opportunities for the reuse of emergent structures as communicative forms” (p. 543). The scenario bears a striking resemblance to Mead’s (1909) “conversation of gestures,” both in its speciﬁcation of gestures as “frozen” parts of an action and in the emphasis placed on complementary interaction as the context in which symbolic meanings and forms intelligibly originate. Mead had noted that imitation is of little importance in social interaction. Goodwin & Goodwin (1996; also see Goodwin 1994) were among the ﬁrst conversation analysts to study talk in technology-rich settings and speciﬁc communities of practice. C. Goodwin (2003) showed how seemingly trivial acts such as pointing to a speck of color on the ground may work only because of the parties’ negotiated reliance on meanings embodied in diverse “semiotic resources.” Goodwin (1994) also showed how acts of professional vision such as noticing a discoloration of soil or seeing violent resistance in Rodney King’s beaten-down body are made possible by the coordinated deployment of linguistic categories and indexical gestures. Goodwin (1995, 2004) examined in detail the artful multimodal practices that enable the family of a man stricken by aphasia to continue to be a fully competent speaker despite having his speakable vocabulary reduced to three words. Since 2000, Goodwin has integrated his research into an increasingly comprehensive theory of action. Crucially, rather than taking the face-to-face situation with its mutual focus as his starting point, he deﬁnes collaborative activity as the primordial site of sociality, that is, a situation in which multiple participants are attempting to carry out courses of action in concert with each other through talk while attending to both the larger activities that their current actions are embedded within, and relevant phenomena in their surround... Human action is built through the simultaneous deployment of a range of quite different kinds of semiotic resources... Strips of talk gain their power as social action via their placement within larger sequential structures, encompassing activities, and participation frameworks constituted through displays of mutual orientation made by the actors’ bodies. The body is used in a quite different way to perform gesture... Both talk and gesture can index, construe or treat as irrelevant, entities in the participants’ surround... [and] material structure in the surround... can provide semiotic structure. (Goodwin 2000, p. 1,489) Goodwin focuses on how the “contextual conﬁguration” (Goodwin 2000) or “contexture of action” (Goodwin 2011) is altered with every action. In the “cooperative transformation zone” (Goodwin 2012) of human activity, each action builds upon and reuses resources provided by prior action: Individual actions emerge from, and use, a consequential past shaped through chains of prior action, providing current participants with a dense, present environment, a rich now, containing many different kinds of resources that can be selectively decomposed, reused and transformed to build a next action, a proposal for how the future will be organized... In so far as such processes preserve with modiﬁcation structures provided by the environments that constitute the point of departure for new action, this process is accumulative, something that is central to the distinctive organization of human culture and society. (Goodwin 2012, pp. 1–2) In the work of both Hutchins and Goodwin, multimodal interaction has been put in historical perspective for the ﬁrst time: In the artifacts from which we build action, including language, www.annualreviews.org • Embodiment in Human Communication 431 histories of action, experiment, and knowledge are sedimented. By enacting them, “preserving structure,” we secure that they remain available for future occasions and thus contribute to the “ratcheting up” of our community’s culture. In Goodwin’s work in particular, the creativity of action ( Joas 1996) also comes into view, the spontaneous ingenuity with which humans “make world” out of the serendipitous constellation of resources that the present moment offers. Although roughly covering the same ground, Hutchins and Goodwin avoid the ﬂattening out of ontology that is characteristic, for example, of actor-network theory (Latour 2005), which indiscriminately distributes agency to people, inanimate objects, and networks. In this respect, actor-network theory runs counter to natural languages, which distinguish between inanimate and sentient beings and whose grammars imply “animacy hierarchies” (Keenan & Comrie 1977). Actor–network theory and other “posthumanist” frameworks have been received with interest by many researchers of multimodal interaction. However, most of those theories and frameworks are committed to
the ethnomethodological maxim that the analytic task is to explicate, not compete with, common-sense reasoning. As a result, they maintain a “humanist” conception of agency, in line with ordinary languages and the “practical sociological reasoning” (Garﬁnkel & Sacks 1970) that is sedimented in them. SEMIOTICS OR ECOLOGY? An open question is whether the ﬁeld will grow along semiotic or ecological paths of inquiry, or how these paths will intersect. Representing linguistic anthropology in the mode of Peircian semiotics, Kockelman (2006) has shown that it is possible to cast the relations of dwelling (“residence”) as sign relations: An affordance can be conceived as a sign, and the action that makes use of it as its interpretation. Kohn (2013) has cast forests as thinking entities, but in Descola’s words, the whole notion of cosmic semiosis may become superﬂuous because what is at stake... is how living and nonliving beings relate to each other according to the types of connection that their physical assets allow. Some of these connections may fall under the rubric “interpretation” or “representation,” if they involve iconic and indexical signs in the widest sense, but most of them will probably be the outcome of nonrepresentational physical and chemical processes. (Descola 2014, p. 271) At stake in human interaction are the concrete enactive couplings between enculturated living bodies and their human and nonhuman environments, not all of which involve or produce signs. To explain the capacity for representation, we must understand how signs evolve from physical action that is “always already” meaningful. Signs are sediments of human action; intelligible, embodied social action does not require that its signiﬁcance be expressed—or expressible—in signs. Signs, according to Heidegger (1926), form a special kind of “equipment,” and the function of a sign is to indicate, or refer to, something, minimally to the action from which it is abstracted (as illustrated by the gestures of infant bonobos). However, bodily actions become intelligible and socially signiﬁcant through the ways in which they couple with the context at hand, and not in the ﬁrst place because they may also refer to this (or some other) context. In other words, semiotic phenomena constitute only parts of processes of embodied communication, and semiotic accounts of embodied communication must be embedded within ecological understandings of bodily being in, and making of, the world (Ingold 2011). The turn to the living body as an agent of embodied communication that this article has described is far from complete. Rather, this turn has the form of an ongoing, often unsuccessful effort. Many submissions to journals betray the immense difﬁculty of understanding and writing about embodied action as inherently cognitive and communicative and about the human self as 432 Streeck “always already” embodied. Such difﬁculty is revealed in the way they continue to refer to interaction participants as using their bodies (or body parts) to communicate meanings, as if the body were an instrument controlled by some “homunculus” residing within it and meaning were some disembodied substance that is translated into material form during the process of communication. Although there is wide consensus about the empirical research agenda and neuroscience provides increasingly more insights into the materiality of the communicating body, the real difﬁculty at present appears to be ﬁnding a postdualist language to formulate our understanding of the communicating human body and of the ways in which human bodies understand one another in social interaction. DISCLOSURE STATEMENT The author is not aware of any afﬁliations, memberships, funding, or ﬁnancial holdings that might be perceived as affecting the objectivity of this review. LITERATURE CITED Alkemeyer T. 2004. Bewegung und Gesellschaft. Zur “Verk¨orperung” des Sozialen und zur Formung des Selbst in Sport und popul¨arer Kultur. In Bewegung: Sozial- und kulturwissenschaftliche Konzepte, ed. G Klein, pp. 43–78. Bielefeld, Ger.: Transcript Alkemeyer T, Br¨ummer K, Kodalle R, Pille T, eds. 2009. Ordnung in Bewegung: Choreographien des Sozialen. K¨orper in Sport, Tanz, Arbeit und Bildung. Bielefeld, Ger.: Transcript Andr´en M. 2010. Children’s Gestures from 18 to 30 Months. Trav. Inst. Linguist. Lund Ser., Vol. 50. Lund, Swed.: Lund Univ. Press Austin J. 1962. How To Do Things with Words. Oxford, UK: Oxford Univ. Press Bateson G. 1956
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1964; Lee & Devore 1968; Cartmill 1974; Lovejoy 1981; Carrier 1984; Shipman & Walker 1989; Sussman 1991; Aiello & Wheeler 1995; Leonard & Robertson 1997; Key & Ross 1999; Aiello & Key 2002; Aiello & Wells 2002; Ant´on et al. 2002; Leonard & Ulijaszek 2002; Pontzer & Wrangham 2004; SteudelNumbers 2006; Snodgrass et al. 2007; Snodgrass & Leonard 2009; Pontzer et al. 2010, 2012, 2014; Orkin & Pontzer 2011; Pontzer 2012). Much of the early technology used to measure energy expenditure required captive subjects, conﬁned to a laboratory. These efforts led to many seminal insights that remain salient today despite the artiﬁcial nature of the laboratory setting (e.g., Kleiber 1947). The development of accurate, noninvasive methods for measuring or estimating energy expenditure in free-living subjects has greatly improved our understanding of activity and energy expenditure in humans and other primates. Although much of this work was motivated by and directed toward estimating nutritional requirements and energy stress among living human populations (e.g., Panter-Brick 1992, 1993; FAO et al. 2001; Dufour & Piperata 2008), anthropologists have applied these methods to reconstructions of energy budgets in nonhuman primates and fossil hominins (e.g., Coelho et al. 1977, Leonard & Robertson 1997, Knott 1998, Key & Ross 1999, Aiello & Key 2002, SteudelNumbers 2006, Froehle & Churchill 2009, Snodgrass & Leonard 2009). This work highlighted the importance of local ecology and activity levels on daily energy requirements and, in turn, on reproductive and somatic investment. More recently, anthropologists and those in public health have been employing the doubly labeled water (DLW) method (Speakman 1997, Int. At. Energy Agency 2009, Westerterp 2010) in measurements of energy expenditure in human and primate populations (e.g., Nagy & Milton 1979; Stein et al. 1988; Singh et al. 1989; Heini et al. 1991, 1996; Kashiwazaki et al. 1995, 2009; Drack et al. 1999; Esparza et al. 2000; Schmid & Speakman 2000; Snodgrass et al. 2006; Pontzer et al. 2010, 2012, 2014; Simmen et al. 2010, 2015; Rosetta et al. 2011). DLW is considered the gold standard for measuring daily energy expenditure in free-living populations because it tracks the body’s rate of carbon dioxide production (and hence caloric expenditure) without encumbering the subject with equipment, conﬁning them to a calorimetry chamber, or extrapolating from activity budgets (Int. At. Energy Agency 2009) (see sidebar Methods for Determining Total Energy Expenditure). Results from DLW studies have often complemented and conﬁrmed results from other approaches, but they have also challenged long-held ideas about the ﬂexibility and plasticity of daily energy expenditure (Westerterp & Speakman 2008, Dugas et al. 2011, Pontzer et al. 2012), suggesting that energy budgets may be more constrained and less responsive to variation in activity levels than is generally thought. These results hold implications for models of energy stress and metabolic syndrome in humans and for variation in metabolic ecology and life history across primates more broadly. In this article I review studies of total energy expenditure (TEE) (kcal/day) in humans and other primates. After brieﬂy discussing the classic laboratory work on metabolic energy expenditure, 170 Pontzer METHODS FOR DETERMINING TOTAL ENERGY EXPENDITURE Doubly labeled water method: Considered the gold standard for measurements of TEE in free-living subjects, the DLW method calculates TEE by measuring the body’s rate of carbon dioxide production (Speakman 1997, Int. At. Energy Agency 2009). Subjects drink a dose of water enriched with 2H and 18O, and the concentrations of these stable isotopes are tracked over time (usually 10–14 days) through a series of urine samples. Both isotopes are lost through water: urine, sweat, and expired water vapor. 18O is also lost via carbon dioxide; thus, the rate of
carbon dioxide production can be calculated by subtracting the rate of 2H depletion from the rate of 18O depletion. The rate of carbon dioxide production (moles/day) is converted to TEE (kcal/day) using the food quotient or respiratory quotient, which can be estimated from dietary information or measured via a respirometry trial. Flex-heart rate method: Recorded using a heart rate monitor and data logger, calibrated heart rate data are used to estimate TEE (Leonard 2003). Prior to the measurement period, a calibration trial in which heart rate and energy expenditure are measured simultaneously, over a range of exercise intensities, is performed for each subject. Energy expenditure is typically measured via mask-based respirometry in these trials. DLW validation studies have shown that ﬂex-heart rate measurements are generally reliable and accurate (e.g., Heini et al. 1991, 1996; Leonard 2003). Respirometry: The body’s consumption of oxygen and production of carbon dioxide are measured by monitoring expired air. Mask-based systems are commonly used to measure the cost of speciﬁc activities (e.g., walking or running). For TEE measurements using respirometry, subjects are conﬁned to a calorimetry chamber, a small, sealed room equipped to monitor the movement and concentration of room air (Ravussin et al. 1982). Respirometry studies provide highly accurate measures of energy expenditure, minute by minute, throughout the study period, but they require subjects to be conﬁned to a calorimetry chamber. Factorial method: TEE estimates are based on an individual’s height, weight, age, and activity budget (FAO et al. 2001). BMR is estimated using available anthropometric data. Time-allocation studies are then used to estimate the mean time per day in various activities (e.g., light work, sleep, walking). Activity data are then converted to energy expenditures using an individual’s estimated BMR and established PAL values for each activity. Factorial estimates of TEE are relatively easy and inexpensive to conduct but have relatively low accuracy; thus, they should be treated as estimates, not measurements, of energy expenditure. I focus on more recent studies of energy expenditure in free-living populations. This review is organized around four broad questions, beginning with proximate determinants of energy expenditure in humans and working toward an integrated ecological and evolutionary perspective on human and primate energy expenditure: 1. Anthropometry of TEE: How much energy do humans and other primates expend each day, and how does this vary with body size, age, and sex? 2. Components of TEE: How do basal metabolic rate (BMR), physical activity, reproduction, maintenance, thermoregulation, and other functions contribute to TEE? 3. Ecological determinants of TEE: How does variation in activity budgets or lifestyle affect TEE, and to what extent is TEE a constrained physiological trait shaped by evolution? 4. TEE and metabolic ecology in humans and other primates: How does TEE shape the life-history strategies and foraging ecology of humans and other primates? ANTHROPOMETRY OF TOTAL ENERGY EXPENDITURE It seems obvious from our daily experience that larger individuals require more energy each day than do smaller individuals, other factors being equal. A positive relationship between energy www.annualreviews.org • Human Energetics 171 expenditure and body size follows intuitively from ﬁrst principles: Larger organisms have more cells, each involved in myriad homeostatic processes, and they also carry more weight and thus must perform more physical work as they move. The question, then, is not whether larger size will tend to increase TEE, but to what extent. Kleiber (1947), in his seminal work on energy expenditure across a range of animals, showed that the relationship between size and energy expenditure was nonlinear. Kleiber focused on measurements of BMR, the rate of energy expended when the organism is at rest. Although BMR is only one component of TEE (often accounting for less than half of daily expenditure among mammals) (see Westerterp & Speakman 2008), it is relatively easy to measure in laboratory settings (usually via respirometry) (see sidebar, Methods for Determining Total Energy Expenditure) and is repeatable and reliable. Kleiber found that BMR increased allometrically, with Mass0.75, a relationship now commonly referred to as Kleiber’s Law. The physiological mechanism underlying the scaling exponent of 0.75 has been debated by comparative biologists ever since. One hypothesis, by West and colleagues (West et al. 1997, Gillooly et al. 2001), proposes that the 0.75 exponent stems from the fractal branching patterns of the energy supply systems (blood vessels) common among animals. More recently, White and colleagues (2009), using phylogenetically informed analyses of
a large, quality-controlled data set of mammalian BMR, reported considerable variation in the scaling exponent among clades, with exponents for the majority of orders falling between 0.67 and 0.75. For the purposes of this review, it is sufﬁcient to note that BMR does not increase linearly with mass and that larger animals use less energy per gram of body mass than do smaller animals. Measurements of TEE using the DLW method (see sidebar, Methods for Determining Total Energy Expenditure), in both wild and captive populations, indicate a similar scaling exponent for mammals. Nagy and colleagues (1999) reported a scaling exponent of 0.77 for eutherian (placental) mammals, with some variation among taxonomic groups. Primate TEE scales with a similar exponent of 0.73 ± 0.03, but the intercept is signiﬁcantly lower, such that TEE for primates (including humans) is 50% lower than expected for a eutherian mammal of the same body mass (Pontzer et al. 2014). As discussed below, this substantial reduction in TEE appears to be related to the remarkably slow life histories evident in humans and other primates. This grade shift in TEE notwithstanding, the scaling exponent (i.e., the allometric slope) does not differ between primates and other eutherian mammals (Pontzer et al. 2014). A similar allometry of energy expenditure is evident within human populations, both in BMR and in TEE. Predictive equations for BMR (Henry 2005, FAO et al. 2001), developed from large diverse human samples, indicate that smaller individuals have, on average, higher massspeciﬁc BMR. Black and colleagues (1996) analyzed DLW measurements from 564 adults living in developed countries (mostly Western Europe and the United States) and developed predictive equations for TEE. The exponent for mass is substantially lower than 1.0, indicating that larger individuals generally expend less energy per gram of body mass than do smaller individuals. For this reason, correcting for body size in analyses of TEE and BMR should be done via multiple regression or ANCOVA, with log-transformed data, rather than simply dividing by mass or fat-free mass (Tsch¨op et al. 2011). The effects of height and sex likely reﬂect effects of body composition on metabolic rate. Adipose tissue is much less active metabolically than other tissues, and both calorimetry chamber studies and DLW studies have shown that the strongest size-related predictor of TEE is lean mass, also called fat-free mass, which often accounts for 65–75% of the variation in TEE between subjects (e.g., Ravussin et al. 1982, Pontzer et al. 2012). Subjects who are taller for a given mass are generally leaner, and men tend to carry less body fat for a given mass than do women. Thus height is positively correlated with TEE, and women tend to have lower TEE for a given body mass. 172 Pontzer Large studies of TEE across a broad age range have noted a small but detectable decline with age, on the order of ∼15 kcal/year for adults older than ∼30 years (Black et al. 1996, Vinken et al. 1999, Elia et al. 2000). Speakman & Westerterp (2010), in the largest analysis of age and TEE to date, argue that this decline does not begin until ∼50 years of age. At least half of the age-related decline in TEE can be ascribed to age-related decline in BMR, suggesting that the decline in TEE is due to age-related changes in body composition (i.e., less lean mass) as well as senescence in cellular activity (Elia et al. 2000, Speakman & Westerterp 2010). Indeed, predictive equations for BMR (e.g., Henry 2005) developed in large, diverse samples indicate similar effects of age, sex, and height as reported for TEE. Reduced physical activity with age, particularly among elderly subjects, appears to contribute to the decline in TEE as well (Elia et al. 2000, Speakman & Westerterp 2010). Variation In and Limits to Total Energy Expenditure Representative TEE values for human populations, measured using the DLW method, are shown in Table 1. Repeated measures of TEE using DLW indicate that average TEE (i.e., mean TEE averaged over a two-week period) (see sidebar, Methods for Determining Total Energy Expenditure) is a relatively stable trait, with a coefﬁcient of variation within subjects of ∼6% (Schoeller & Hnilicka 1996).
The coefﬁcient of variation between subjects is considerably greater, approximately 15% (see Table 1) (Pontzer et al. 2012). In fact, variation in TEE between subjects within a population is considerably greater than the variation between populations, as evident in Table 1. Only 50–75% of the variation in TEE between subjects is explained by anthropometric variables, particularly fat-free mass (Black et al. 1996, Dugas et al. 2011, Pontzer et al. 2012). Measurements of physical activity can explain some of the remaining variation in TEE, but this is dependent on the methods used to measure activity and the population being examined. For example, GPS-based measurements of daily walking distance were not correlated with TEE in an adult sample (n = 30) of Hadza hunter-gatherers, after accounting for fat-free mass (Pontzer et al. 2012, 2015). Accelerometer measurements of activity account for some of the variation in TEE (Butte et al. 2012, Plasqui et al. 2013), but the amount of variation explained is generally modest, ranging from 4% to 23% (Plasqui et al. 2013). Indeed, accelerometry-based estimates often deviate substantially from measured TEE (Leenders et al. 2006). Genetic variation likely accounts for some of the variation in TEE as well. In a study of 294 elderly subjects, Tranah and colleagues (2011) found that subjects with mitochondrial DNA haplotypes of African origin had ∼10% lower TEE than those with mitochondrial DNA haplotypes of European origin, after correcting for body size and activity. Variation in hormone proﬁles undoubtedly affects energy expenditure, but endocrine regulation of BMR and TEE is complex and understudied. Several hormones, including thyroid hormones (thyroxine and triiodothyronine), estrogen, testosterone, and growth hormone, promote metabolism and tissue growth (Widmaier et al. 2004) and can be expected to increase energy expenditure. In particular, thyroid hormone is a primary regulator of metabolic rate and of heat production in response to cold exposure. However, although extreme levels of thyroid hormone affect BMR and TEE, normal variation in thyroid hormone levels in healthy adults is not necessarily correlated with variation in BMR or TEE (Tagliaferri et al. 2001, Klieverik et al. 2009, Leonard et al. 2014, Spadafranca et al. 2015). Similarly, growth hormone has positive effects on BMR and TEE (Gregory et al. 1991, 1993; Chong et al. 1994), but variation in growth hormone levels among adults, even those with clinically low levels, does not necessarily predict variation in TEE (Chong et al. 1994). Santosa and colleagues (2010) manipulated testosterone and estrogen levels in older men and found no difference in BMR when these hormones were completely www.annualreviews.org • Human Energetics 173 Table 1 Mean TEE (measured using the doubly labeled water method) and PAL ( ± standard deviation) in human populations Population N Sex Mass (kg) BMI Age (years) TEE (kcal/day) PAL Reference(s) Combined populationsa Developing countries 10 M 66.1 ± 2.7 22.7 ± 1.0 32.0 ± 3.3 2,940 ± 96 1.88 ± 0.06 Dugas et al. 2011 Developed countriesb 42 M 81.3 ± 2.0 26.0 ± 0.6 34.5 ± 1.7 3,226 ± 72 1.81 ± 0.03 Dugas et al. 2011 Developing countries 13 F 59.1 ± 2.0 24.3 ± 0.7 33.2 ± 2.7 2,223 ± 48 1.70 ± 0.03 Dugas et al. 2011 Developed countriesb 102 F 72.6 ± 3.2 26.6 ± 0.4 35.1 ± 1.3 2,462 ± 24 1.72 ± 0.02 Dugas et al. 2011 Extremely low physical activityc Enforced bed-rest, healthy subjects 8 F 52.6 ± 1.4 19.8 ± 0.4 33.9 ± 0.8 1,702 ± 186 1.37 ± 0.06 Bergouignan et al. 2010, 2013 Demented elderly 7 F – – – 1,242 ± 167 1.27 ± 0
.14 Black et al. 1996 Nonambulatory adolescents 11 M, F – – – 1,458 ± 239 1.22 ± 0.18 Black et al. 1996 Extremely high physical activityc,d Tour de France cyclists 4 M 67.8 – – 8,054 ± 143 4.69 ± 0.20 Black et al. 1996, Cooper et al. 2011 Arctic explorers 2 M 62 – 42.5 7,910 ± 358 4.47 ± 0.06 Black et al. 1996, Cooper et al. 2011 Swedish national nordic skiers 4 F 54.2 ± 5.4 – 25 ± 2 4,374 ± 550 2.81 ± 0.09 Black et al. 1996, Cooper et al. 2011 Runners in training 9 F 51.9 ± 3.7 – 26 ± 3 2,820 ± 311 2.03 ± 0.16 Black et al. 1996, Cooper et al. 2011 Foragers and farmersc Hadza hunter-gatherers 13 M 50.9 ± 5.4 20.2 ± 1.3 33.1 ± 14.4 2,649 ± 395 2.04 ± 0.28e Pontzer et al. 2015 Hadza hunter-gatherers 17 F 43.4 ± 6.4 20.1 ± 1.7 40.0 ± 19.4 1,877 ± 364 1.76 ± 0.28e Pontzer et al. 2015 Bolivian farmersf 11 M 54.7 ± 2.9 21.2 ± 1.6 49.1 ± 20.9 2,866 ± 435 2.08 ± 0.26 Pontzer et al. 2012 Bolivian farmersf 14 F 48.1 ± 6.9 20.7 ± 3.2 43.9 ± 21.8 2,469 ± 315 2.11 ± 0.30 Pontzer et al. 2012 Gambian farmersg 8 M 61.2 ± 3.6 21.2 ± 0.9 25.0 ± 1.4 3,879 ± 351 2.40 ± 0.14 Heini et al. 1996 Gambian farmersg 10 F 49.4 ± 1.7 – 30.0 ± 2.2 2,407 ± 196 1.98 ± 0.13 Singh et al. 1989 Abbreviations: BMI, basal metabolic index; PAL, physical activity level; TEE, total energy expenditure. aN represents the number of populations included. bRestricted to cohorts with a mean age <65 years (see Dugas et al. 2011). cN represents the number of individuals measured. dSubjects lost weight during these periods (0.2–1.3 kg/week) (see Cooper et al. 2011). ePAL is calculated using estimated basal metabolic rate. fCombines periods of high and low farming activity. PAL was 11% greater during high versus low activity (Kashiwazaki et al. 2009). gMeasured during periods of high farming activity. 174 Pontzer suppressed versus maintained at normal levels. More work is needed to disentangle the actions and interactions of individual hormones in the regulation of BMR and TEE in free-living, healthy humans. Several studies have examined subjects at the extremes of physical activity to investigate the limits to sustained TEE in humans. To compare across subjects and populations of different body mass and age, daily energy expenditure in these studies is often expressed as physical activity level (PAL), calculated as the ratio of TEE/BMR. At the low end of the range, patients who are conﬁned to bed rest have a PAL of 1.2–1.3, whereas athletes and military personnel achieve a maximum PAL of ∼5 during competition (Black et al. 1996, Hammond & Diamond 1997, Cooper et al. 2011). In addition to documenting the limits of human physiology, these studies point to two important aspects of our metabolism. First, even inactive subjects exhibit a PAL of 1.2–1.3, rather than the theoretically lowest value of 1.0. Second, even in well-provisioned athletes with unlimited food supply, there is a limit to the rate at which the body can take in and expend energy. COMPONENTS OF TOTAL ENERGY EXPENDITURE Basal Metabolic Rate BMR is the body’s lowest rate of
energy expenditure, reﬂecting summed energy requirements of the body’s organ systems at rest. Organs and tissues differ in their resting energy requirements, and expensive tissues such as the brain, gut, kidneys, heart, and liver account for a correspondingly large portion (Elia 1992, Aiello & Wheeler 1995, Wang et al. 2011). Accordingly, fat-free mass is a strong predictor of BMR (e.g., Ravussin et al. 1982). By deﬁnition, BMR is measured after a period of rest (usually after a full night’s sleep) and 10–12 h of fasting, with the subject awake, lying down, and at rest in a thermoneutral (22–26◦C) room; the subject must also be free from psychological or other stress and accustomed to the apparatus (Henry 2005). Measurements taken outside of these conditions (e.g., at midday or while standing or seated) are sometimes called resting metabolic rate (RMR) and will be elevated relative to BMR. Mean PAL for healthy adult populations in developed countries generally ranges from 1.6 to 1.9 for men and from 1.6 to 1.7 for women (Black et al. 1996, Dugas et al. 2011) (Table 1), meaning that BMR accounts for more than half of TEE for most subjects. Moreover, as noted above, subjects restricted to bed rest generally exhibit PAL values of 1.2–1.4 owing to the marked diurnal increase in RMR (Table 1). As a result, PAL is somewhat of a misnomer, because a substantial portion derives not from physical activity but from other generally unseen physiological processes. Similarly, activity energy expenditure (AEE), calculated as the difference between TEE and BMR (Black et al. 1996), includes energy expenditure on physiological activity other than movement and muscle activity. Physical Activity Muscles at rest use relatively little energy (Elia 1992, Wang et al. 2011), but during physical activity they can raise the body’s rate of energy expenditure by more than an order of magnitude above BMR. A compendium of energy costs for a broad range of activities is regularly updated by Ainsworth et al. (2000). Still, calculating the proportion of TEE expended in physical activity is difﬁcult, because recording all muscle activity is challenging and estimating its cost introduces error. Further, as noted above, common measures of physical activity, such as PAL and AEE, overestimate the true contribution of physical activity to TEE by ignoring diurnal ﬂuctuation in RMR. www.annualreviews.org • Human Energetics 175 One approach to estimating the contribution of physical activity to TEE is to subtract the PAL of subjects restricted to bed rest from the PAL of healthy, active adults. Given that a completely inactive adult has a PAL of ∼1.3 (Black et al. 1996) (Table 1), physical activity in healthy adults (PAL = 1.6–1.9) must contribute an additional 0.3–0.6 PAL, equivalent to 19–32% of TEE. Note that this ﬁgure includes the cost of walking, climbing stairs, and other gross motor activities as well as that of less-noticeable activities (e.g., sitting, typing, ﬁdgeting). Levine (2004) has argued that the daily energetic cost of these minor activities constitutes an important component of TEE, which he terms nonexercise activity thermogenesis. Growth Butte (2000) provides a thorough overview of the energy costs of growth for humans, synthesizing a large body of DLW measurements. Growth costs are generally estimated at 20 kJ/g of new tissue deposited (Butte 2000). By combining TEE measured via DLW (which does not capture the energy invested in new tissue) with weight velocities for growing children from Tanner and colleagues (1996), Butte calculated the proportion of daily energy requirements allocated to growth in healthy human children. For both boys and girls, growth accounted for 28–39% of daily energy requirements during the ﬁrst 3 months of infancy, falling to 4–5% of daily energy throughput at 1 year and then to ∼2% or less by age 2. These estimates are for well-nourished children in developed countries and may be somewhat lower for children with slower growth rates. These rough estimates of growth cost are useful but may obscure many important costs of development. For example, Kuzawa and colleagues (2014), using data from positron emission tomography studies of brain glucose uptake, found that the energy requirements of the developing human brain peak in early childhood, around age 5, accounting for more than 40% of TEE. This peak in brain energy use is associated with synapse development
and learning, rather than with the deposition of new brain tissue (brain growth is nearly complete by age 5). Notably, this period of high metabolic activity in the brain corresponds to a period of slow growth in the body overall, strongly suggesting that the high metabolic demands of the developing human brain lead to a slowing of growth and an extension childhood (Kuzawa et al. 2014). Similar studies of developmental cost in other organ systems are needed to provide an integrated perspective of growth and metabolism in humans and other primates. Reproduction The energetic costs and consequences of pregnancy and reproduction in both humans and nonhuman primates have received a great deal of attention (see Ellison 2001, 2003; Dufour & Sauther 2002; Butte & King 2005; Martin 2007; Dunsworth et al. 2012; Emery Thompson 2013). Reproduction is incredibly expensive for humans, with an estimated total metabolic cost of pregnancy of ∼78,000 kcal, and peak lactation costs of ∼630 kcal/day (Butte & King 2005). The cost of lactation is offset by the mobilization of fat reserves, such that daily energy requirements during lactation peak at ∼450 kcal/day, similar to the daily energy cost of pregnancy during the third trimester (Butte & King 2005). These costs bring human mothers to the brink of unsustainable TEE, with a PAL of ∼2.1 (Hammond & Diamond 1997). Dunsworth and colleagues (2012) have argued that gestation length in humans is limited by the mother’s capacity for energy throughput, with birth occurring just as the fetus threatens the mother’s metabolic ceiling (and see Ellison 2001). Under this scenario, the relatively underdeveloped, altricial nature of human newborns is a consequence of the mother’s metabolic limits; longer gestations and greater development in utero simply cannot be sustained. 176 Pontzer With reproduction so energetically expensive, humans and other primates have evolved a suite of physiological strategies for limiting its costs and reducing the likelihood of failure. Ellison (1990, 2001, 2003) and others have shown that human ovarian function is remarkably sensitive to energy availability and stress, reducing the likelihood of conception during unfavorable conditions. Energy investment during gestation and lactation is relatively buffered against maternal energetic stress, but gestation length, birth weight, and the duration of lactational amenorrhea all respond to some degree to energy availability (Ellison 2003). Milk content and volume also appear to be relatively buffered, but more studies of milk composition across the lactation period are needed (Hinde & Milligan 2011). This buffering requires decreased metabolic throughput in other organ systems. Mothers in traditional farming populations, with physically demanding lifestyles, may reduce BMR during pregnancy and lactation to keep total daily energy requirements in check (Heini et al. 1991, Dufour & Sauther 2002). Immune Function Mounting an immune response to infection requires energy, but although the physiological responses to disease have been intensively studied, their energy costs are not well characterized (Muehlenbein 2010, Muehlenbein et al. 2010). Work in nonhuman mammals suggests metabolic rate increases of 10–50% are common in response to infection (see Muehlenbein et al. 2010). Muehlenbein and colleagues (2010), in one of the few human studies of immune function energetics, report an 8% increase in RMR among nonfebrile men with relatively minor respiratory tract infections. Torine and colleagues (2007) compared premature infants with sepsis to age-matched healthy controls and found 43% greater TEE among those ﬁghting infection. Digestion The energy costs of digestion, termed the thermic effect of food (TEF) (Kinabo & Durnin 1990), are typically estimated at 10% of the caloric value of the meal consumed (Black et al. 1996). Kinabo & Durnin (1990) reported TEF values ranging from 7% to 9% of the energy consumed for a range of diets, with no effect of nutrient composition on TEF. The majority of TEF reﬂects the work done in digestion and transport of nutrients, but approximately 20% of TEF derives from the activation of the sympathetic nervous system (Welle 1995). Calculations of AEE sometimes account for TEF by reducing TEE by 10% prior to subtracting BMR, such that AEE = 0.9 TEE −BMR. Thermoregulation In conditions outside of the thermoneutral zone (22–26◦C for lightly clothed human subjects) metabolic rate increases to either heat or cool the body and defend a core temperature of 37◦C. The metabolic
responses to acute cold and heat exposure have been relatively well studied in laboratory settings, but in normal daily life, clothing, housing, and other cultural innovations greatly reduce thermoregulatory demands. Nonetheless, Leonard and colleagues (2002) showed that circumpolar populations, living in exceptionally cold environments, exhibit elevated BMR. Indigenous subjects showed a greater elevation in BMR (women: 17%, men: 19%) than nonindigenous subjects (women: 5%, men: 14%) after controlling for fat-free mass, suggesting a genetic component to cold adaptation in native populations. More recently, in a study of the Yakut population in Siberia, Leonard and colleagues (2014) reported a 6% increase in BMR during winter months among adults 19–49 years, but no difference in older adults. The elevation in BMR in response to cold is likely due in part to the activity of brown adipose tissue (Saito 2013, Muzik www.annualreviews.org • Human Energetics 177 et al. 2013). It remains unclear whether these increases in BMR result in corresponding increases in TEE. In a study of Dutch adults, Plasqui & Westerterp (2004) found similar TEE in summer and winter despite increased winter BMR. ECOLOGICAL DETERMINANTS OF TOTAL ENERGY EXPENDITURE It is often assumed that TEE reﬂects variation in ecology, particularly the level of physical activity, among individuals and populations. Indeed, this is the foundational assumption underlying factorial models of TEE (FAO et al. 2001) (see sidebar, Methods for Determining Total Energy Expenditure), which have been widely adopted in human and nonhuman primate ecology and paleoanthropology. However, factorial estimates are generally no more reliable for predicting TEE among individuals than are estimates from body mass (r2 values of 0.2–0.3 within populations) (see Leonard et al. 1997, Walsh et al. 2004) and tend to underestimate mean TEE, particularly in physically active populations (Leonard et al. 1997, Kashiwazaki et al. 2009). Similarly, as noted above, accelerometry-based measures of physical activity add little to TEE estimates based on fat-free mass (Plasqui et al. 2013), and accelerometry-based estimates of TEE often deviate substantially from observed values (Leenders et al. 2006). Empirical measurements of TEE in a broad range of populations and species indicate that the relationship between ecology and TEE is much more complex than factorial models and accelerometry-based estimates of TEE allow. Intervention studies regularly show a short-term increase in TEE among sedentary individuals enrolled into exercise programs (Ross & Janssen 2001). But over the long term, this effect is diminished as the body adapts to the increased workload. For example, Westerterp and colleagues (1992) measured TEE and BMR in sedentary men and women enrolled in a 40-week training program. Subjects ran three times per week, and the duration of these running bouts increased over the course of the study, preparing the subjects to run a half-marathon. TEE increased over the ﬁrst 8 weeks of training but then plateaued for the duration of the study even as the exercise workload increased. Instead, BMR (measured during sleep) decreased to accommodate the increased exercise (Westerterp et al. 1992); such metabolic adaptation to increased activity is thought to be a major reason that exercise-based weight loss programs fail to produce expected weight reduction over the long-term (Ross & Janssen 2001). Similar metabolic responses to increased activity have been reported in laboratory studies for a range of birds and mammals (Pontzer 2015). This dynamic, adaptive view of metabolic physiology is supported by comparative studies of TEE across populations that differ in habitual activity level. Dugas et al. (2011) found no effect of socioeconomic development (a proxy of physical activity) on TEE in a global sample of 183 same-sex cohorts. My colleagues and I (Pontzer et al. 2012) found no difference in TEE between traditional Hadza hunter-gatherers and Westerners, after accounting for effects of lean mass, age, and sex. That same analysis (Pontzer et al. 2012) found that subsistence farmers had somewhat higher TEE, but the effect was variable; for example, among Bolivian farmers, men did not exhibit elevated TEE, but women did. This similarity in TEE among populations with different levels of physical activity is not restricted to humans. In a recent analysis of 19 populations representing 17 species of primate, controlling for body mass, my colleagues and I (Pontzer et al. 2014) found no difference in TEE between captive and wild primate populations
. These results indicate that the effects of habitual physical activity are muted by dynamic physiological responses that work to maintain TEE within a narrow range. This constrained TEE model, in turn, suggests that energy allocation among physiological activities is responsive over the long-term to changes in physical activity (Pontzer 2015). Indeed, physiological adaptation to increased workload is well documented. As noted above, Ellison and colleagues (Ellison & Lager 178 Pontzer Methods for Determining Total Energy Expenditure); it assumes that all costs are additive and cannot account for adaptive and dynamic changes in allocation. Factorial estimates of TEE should be used cautiously for living populations and, ideally, validated against DLW measurements within the study population. Using the factorial method to estimate TEE for nonhuman primates or fossil hominins (e.g., Leonard & Robertson 1997, Key & Ross 1999, Aiello & Key 2002, SteudelNumbers 2006, Snodgrass et al. 2007, Froehle & Churchill 2009) raises particular challenges, as validation against empirical measurements of TEE is often difﬁcult or (for extinct populations) impossible. Second, public health policy, particularly as it pertains to obesity and metabolic syndrome, may be improved by adopting an adaptive, dynamic view of metabolic physiology. The importance of regular exercise in promoting and maintaining good health is well established, but the mechanisms involved remain an area of active research. If TEE is constrained, increasing exercise energy expenditure would have a muted effect on TEE but would reduce energy expenditure in other, potentially harmful, physiological activities. Consistent with this hypothesis, exercise is associated with a reduction in inﬂammation response and other metabolic activity that is implicated in the development of chronic disease (Michigan et al. 2011, Roemmich et al. 2014, Silverman & Deuster 2014). Population differences in energy allocation, rather than in TEE, could underlie low rates of cardiovascular disease, diabetes, and other chronic illness and age-related decline in traditional populations (e.g., O’Dea 1991, Vasunilashorn et al. 2010, Pontzer et al. 2012, Pisor et al. 2013). Conversely, if physical activity has a limited effect on TEE, strategies for weight loss and healthy weight maintenance should focus on diet and food energy intake (Luke & Cooper 2013). Third, insofar as TEE reﬂects physiological constraints, the physiological limits of TEE may be shaped in large part by genetics and may therefore be subject to evolution through natural selection (Sibly & Brown 2007, Pontzer & Kamilar 2009). Consequently, variation in TEE among species may reﬂect evolved, systemic changes in metabolic physiology rather than differences in physical activity. These evolved metabolic strategies are central to the ecology and physiology of a species. www.annualreviews.org • Human Energetics 179 103 105 104 103 102 101 100 102 101 100 10–1 10–2 10–3 Body mass (kg) Total energy expenditure (kcal/day) Terrestrial carnivores Nonprimates y = 209x 0.77; R2 = 0.96 Aquatic carnivores NONPRIMATES PRIMATES Wild Primates y = 107x 0.73; R2 = 0.97 Captive Artiodactyls Rodents Bats Other Sloths Aardwolves Orangutans Figure 1 Total energy expenditure (TEE) versus body mass for primates (n = 19 populations, 17 species) and nonprimate eutherian mammals (n = 86 species). Data from Pontzer et al. (2014) and Simmen et al. (2015). Separate trend lines for primates (red ) and nonprimates ( gray) are shown. Trend line for primates excludes mouse lemurs (Microcebus murinus). See Pontzer et al. (2014) for an in-depth comparison of primate and nonprimate regressions. Among primates, orangutans are notable for having low TEE, which may reﬂect a metabolic strategy to reduce the risk of starvation during periods of low food availability (Pontzer et al. 2010). Two eutherian mammals >1 kg fall below the primate trendline: aardwolves (Proteles cristaus) and sloths (Bradypus variegatus). Sloths and aardwolves, and perhaps orangutans, also exhibit low basal metabolic rate (BMR) (Nagy & Montgomery 1980, Williams et al. 1997, Pontzer et al. 2010). EVOLUTION OF TOTAL ENERGY EXPENDITURE IN HUMANS AND OTHER PRIMATES Considerable variation in TEE has been documented among species and
clades, even when controlling for body size (Nagy et al. 1999, Pontzer et al. 2014). As discussed above, my collaborators and I have recently shown that primates, including humans, expend only half of the energy expected for a placental mammal of similar body mass (Pontzer et al. 2014) (Figure 1). The magnitude of difference is too large to be a result of differences in physical activity. To put human TEE in context, predicted TEE for a 65-kg eutherian mammal is 5,550 kcal/day (Pontzer et al. 2014), which exceeds all but the most extreme feats of human endurance and is clearly not sustainable over the long-term (Black et al. 1996, Cooper et al. 2011). As with human populations, lifestyle differences appear to have little effect on TEE in nonhuman primates. Captive (zoo and sanctuary) 180 Pontzer and wild populations have similar TEE, and daily energy intake among wild populations closely matches TEE measured in captivity (Pontzer et al. 2014). The reduction in TEE is found across the primate order, indicating that it evolved very early in the primate radiation. BMR does not show the same reduction across primates; monkeys and apes have BMR similar to other placental mammals, whereas BMR among lemurs and lorises is marginally lower (Snodgrass et al. 2007, Pontzer et al. 2014). My colleagues and I (Pontzer et al. 2014) have hypothesized that this divergence in BMR and TEE reﬂects the evolutionary increase in brain size among anthropoid primates. Initially, early primates, which were small bodied and had unremarkable brain sizes, evolved a reduced metabolic rate that would have decreased both BMR and TEE. As brain size later increased in primates, particularly in anthropoids, BMR also increased, reﬂecting the high metabolic cost of brain tissue (Elia 1992, Wang et al. 2011). Today, the highly encephalized anthropoid primates evince BMR similar to that of other placental mammals, whereas the less-encephalized strepsirhine primates retain somewhat lower BMR. The grade shift in TEE accounts for the slow rates of growth, reproduction, and aging evident among primates. Primates have the slowest life histories of any eutherian order (Charnov 1993, Charnov & Berrigan 1993). However, when rates of growth, reproduction, and senescence are plotted against metabolic rate rather than body mass, this difference in life history falls away (Pontzer et al. 2014). The ultimate evolutionary reasons for changes in TEE remain largely unresolved and may well vary among different lineages (Brown et al. 2004, Sibly & Brown 2007, Pontzer & Kamilar 2009). Increased TEE may support greater reproductive output and thus be favored when food availability is high (Mueller & Diamond 2001), whereas lowering TEE may reduce the risk of starvation during food shortages as well as the risks, including predation, associated with foraging (Sibly & Brown 2007, Pontzer & Kamilar 2009). Species with particularly low TEE may be informative here. Two nonprimate eutherian mammals fall below the primate TEE/body mass trend line: three-toed sloths (Bradypus variegatus) and aardwolves (Proteles cristatus) (Figure 1). Sloths are notoriously sedentary, and their extremely slow metabolism may be part of a slow, cryptic lifestyle that reduces the risk of predation (Nagy & Montgomery 1980). Aardwolves have a highly derived diet, feeding almost exclusively on termites; their low TEE is thought to be an adaptation for reducing energy requirements and the risk of starvation (Williams et al. 1997). Similarly, orangutans (Pongo pygmaeus) exhibit very low TEE, even for a primate (Figure 1), and my colleagues and I (Pontzer et al. 2010) have proposed that their low metabolic throughput is an adaptation to reduce the risk of starvation during the severe but unpredictable periods of food shortage in their native habitats. These extreme cases suggest TEE may be a target of selection in the context of foraging ecology and predation, but the evolutionary relationships linking foraging ecology, TEE, and life-history strategies are not well understood and remain an important focus for future research. Larger samples are needed to examine evolutionary changes in TEE within the hominoid clade, but the available evidence suggests that TEE has decreased substantially in orangutans and may have increased in our own lineage, independent of changes in mass and activity (
Pontzer et al. 2010, 2014). Changes in TEE—the size of the daily “energy budget”—would hold important implications for reconstructing hominin evolutionary history (Pontzer 2012). Ecophysiological models for increased brain size and reproductive output in hominins have emphasized energetic trade-offs between brain and gut size (e.g., Aiello & Wheeler 1995, Isler & van Schaik 2009) or locomotor cost (Navarrete et al. 2011), an approach that assumes the daily energy budget, TEE, is ﬁxed. However, if the energy budget can expand and contract over evolutionary time, these models need to account for potential changes in TEE as well as trade-offs in energy investment and allocation. www.annualreviews.org • Human Energetics 181 SUMMARY TEE in humans and other primates has traditionally been viewed as a simple product of body size and activity level (FAO et al. 2001). Although this perspective persists in some areas of ecology and public health, a large and increasing set of studies from free-living populations across a broad range of populations and species provides a much more dynamic and complex view of our metabolic physiology. TEE in humans and other primates is remarkably low compared with that of other placental mammals, a previously unappreciated aspect of the primate phenotype that appears to correspond with primates’ distinctively slow life histories. Physical activity is an important component of TEE, but variation in physical activity among individuals or populations has less effect on TEE than is often assumed. Instead, in humans and other species TEE appears to be maintained within a relatively narrow, evolved, and species-speciﬁc physiological range. The ecological and evolutionary pressures shaping TEE and BMR in humans and other primates are important areas for future research and discovery. DISCLOSURE STATEMENT The author is not aware of any afﬁliations, memberships, funding, or ﬁnancial holdings that might be perceived as affecting the objectivity of this review. ACKNOWLEDGMENTS I thank David Raichlen, Dale Schoeller, William Wong, Peter Ellison, and Amy Luke for insightful conversations that have helped shape my thinking on human and primate energetics. LITERATURE CITED Aiello LC, Key C. 2002. Energetic consequences of being a Homo erectus female. Am. J. Hum. Biol. 14:551– 65 Aiello LC, Wells JCK. 2002. Energetics and the evolution of the genus Homo. Annu. Rev. Anthropol. 31:323– 38 Aiello LC, Wheeler P. 1995. The expensive-tissue hypothesis: the brain and the digestive system in human and primate evolution. Curr. Anthropol. 36:199–221 Ainsworth BE, Haskell WL, Whitt MC, Irwin ML, Swartz AM, et al. 2000. Compendium of physical activities: an update of activity codes and MET intensities. Med. Sci. Sports Exerc. 32:S498–504 Ant´on SC, William RL, Marcia LR. 2002. An ecomorphological model of the initial hominid dispersal from Africa. J. Hum. Evol. 43:773–85 Bergouignan A, Antoun E, Momken I, Schoeller DA, Gauquelin-Koch G, et al. 2013. Effect of contrasted levels of habitual physical activity on metabolic ﬂexibility. J. Appl. Physiol. 114:371–79 Bergouignan A, Momken I, Schoeller DA, Normand S, Zahariev A, et al. 2010. Regulation of energy balance during long-term physical inactivity induced by bed rest with and without exercise training. J. Clin. Endocrinol. Metab. 95:1045–53 Black AE, Coward WA, Cole TJ, Prentice AM. 1996. Human energy expenditure in afﬂuent societies: an analysis of 574 doubly-labelled water measurements. Eur. J. Clin. Nutr. 50:72–92 Bribiescas RG. 2001. Serum leptin levels and anthropometric correlates in Ache Amerindians of eastern Paraguay. Am. J. Phys. Anthropol. 115:297–303 Brown JH, Gillooly JF, Allen AP, Savage VM, West BG. 2004. Toward a metabolic theory of ecology. Ecology 85:1771–89 Butte NF. 2000. Fat intake of children in relation to energy requirements. Am. J. Clin. Nutr. 72:1246S–52S Butte NF, Ekelund U, Westerterp KR. 2012. Assessing physical activity using wearable monitors
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of these technologies on contemporary archaeological practice. This article reﬂects on how the democratization and proliferation of HDSM opens various applications and greatly broadens the set of problems being addressed explicitly and directly through shape and place. 347 INTRODUCTION Shape, Space, and Place in Archaeology What is so revolutionary and wonderful about recording the shapes of things and their places? The ability to record these fundamental archaeological data has been around since the beginning of the discipline. More than two generations ago, Gordon Willey stated that the objectives of archaeology are “approached by the study and manipulation of three basic factors: form, space and time” (Willey 1953, p. 361). In 1960, Albert Spaulding identiﬁed what he termed the “dimensions” of archaeology. He deﬁned dimension as “an aspect or property of the subject matter which requires its own special measuring device” (Spaulding 1960, p. 438). In the same way that radiocarbon and related dating techniques profoundly changed the structure of archaeology by providing the ability to precisely and accurately measure the dimension of time, we argue that high-density survey and measurement (HDSM) will impact the other two dimensions: space and form. Furthermore, the rapidity and ease with which the technologies needed to measure these dimensions can now be deployed move spatial and morphological data from specialist or exceptional recording to the norm. This democratization and proliferation are fundamentally important because they open up various applications and greatly broaden the set of problems being addressed. What Is HDSM? HDSM incorporates a growing suite of technologies that facilitate the measurement, recordation, and analysis of the spatial, locational, and morphological properties of objects, sites, structures, and landscapes with unprecedented spatial resolution and precision. Key technologies today include airborne lidar, real-time kinematic global navigation satellite system and global navigation satellite system (GNSS) and global positioning system (GPS) survey for projects working at the landscape scale, robotic total stations, terrestrial “laser” scanning, and unmanned aerial vehicle (UAV)-based SfM/CRP or scanning for projects at the medium (site) scale, and structured light scanning and close range photogrammetry [CRP, also known as structure from motion (SfM)] for work at the intra-site to object scale (Figure 1). In short, collectively these technologies are supporting data acquisition for recording the form, location, and orientation of archaeologically relevant remains (mobile objects, landforms, architecture) across a number of scales. The enterprise of capturing rich data on form and place has thus moved from the resource-expensive/difﬁcult/time-intensive quadrant toward the low-resource/straightforward/low-time-investment quadrant. These changes are not mere improvements in our former methods but represent a fundamental shift in how we create and engage with the archaeological record. Rather than provide quickly dated detail on the individual technologies, we include current references, summarized by technology in Table 1, and move directly to the essentials of HDSM data. At the most basic level, all the technologies record relative x,y,z positions on the surfaces of an entity or entities. The returns, summarized or digitally represented as points or pixels or voxels, are spaced closely enough to readily suggest the form and morphology of the entity, and the returns may be geolocated through the inclusion of control points or by spatial tagging at a more generalized scale. In some cases, spectral properties or other physical properties of the elements are recorded by the same signal that is providing the spatial information; however, for the purposes of this article, we exclusively consider the x,y,z data and their derivatives. History of HDSM Technology in Archaeology The history of recording shape and place in archaeology is also a history of archaeological survey and illustration. In this light, HDSM’s precursors include architectural and plane table survey, 348 Opitz· Limp a b c d Figure 1 Examples of high-density survey and measurement (HDSM) data. (a) Terrestrial laser-scanning data at Chaco Canyon, United States. (b) Airborne laser-scanning data from Gozo. (c) Structure from motion data from Gabii, Italy. (d ) Head pot from the Hampson Museum Collection. drawings and line drawings of artifacts (see Adkins & Adkins 1989 and Dobie & Evans 2010). Within this long history, the crucial transition from traditional survey and measurement (SM) to HDSM is marked by a series of technological watersheds (see Table 2). The impact of these technological developments on disciplines for which ﬁeldwork, often in remote locales, is central cannot be overstated. Vitek (2013), commenting on developments in geomorphology, highlights that “[t]he ability to know exactly where you are in the ﬁeld is now taken for granted,” a far cry from “the beginning of the twentieth century
, [when] the amount and quality of maps available was minimal” (p. 24). The ﬁeld reached this state over a series of technological leaps. To focus on the more recent developments in HDSM speciﬁc to archaeology, we turn to the literature. There are three striking patterns in the growth of the literature on HDSM in archaeology: Conference proceedings rather than traditional journals dominate, the center of gravity in research, development, and applications was and is in Europe, and the literature involving HDSM in North America is just now beginning to explode. There are numerous examples of early www.annualreviews.org • Implications for Practice and Theory 349 References Real-time kinematic GNSS General introductions: Henning 2011, Donahue et al. 2013, TSA 2012 Archaeological applications: Barratt et al. 2000, Leckebusch 2005, Yun-sheng & Chang-qing 2008, Roosevelt 2014 Robotic total stations Archaeological applications: Kvamme et al. 2006 Airborne laser-scanning lidar General introduction: Vosselman & Maas 2010 Archaeological applications: Opitz & Cowley 2013 Sources in United States: USGS et al. 2011, Snyder 2012 Terrestrial laser-scanning General introduction: Barber & Mills 2007, Engl. Herit. 2011, Buckley et al. 2008, Van Genechten 2008 Archaeological applications: Limp et al. 2011, Remondino & Campana 2014; see also International Society for Photogrammetry and Remote Sensing (http://www.cage.curtin.edu.au/∼gordonsj/isprs_wgv3/) Close-range photogrammetry/SfM General introduction: Hanke & Grussenmeyer 2002 Archaeological applications: Ioannides et al. 2014, Remondino & Campana 2014 Abbreviations: GNSS, global navigation satellite system; SfM, structure from motion. investigations in the technologies that compose HDSM (examples include Anderson 1982, Barber & Mills 2001, Doneus & Neubauer 1998, Ebert 1984, Gisiger et al. 1997, Lagerqvist 1999), but for all practical purposes, they did not have a signiﬁcant footprint in archaeology until the early 2000s and in North America until the second decade of the twenty-ﬁrst century. North America has lagged behind Europe and the rest of the world for several potential reasons. Perhaps one of the most signiﬁcant was the early realization in Europe that HDSM was a key method in heritage management and interpretation, especially where there was a preponderance of architectural remains. Over the past decades, the European Union has funded many multi-institutional research programs focused on the development and application of HDSM, investing many tens of millions of euros to do so. Institutional linkages between archaeologists and HDSM practitioners are also often strong in Europe, where heritage case studies often serve as vehicles for research problems in computer vision and other computational research efforts (cf. http://www.cd-coform.eu). Table 2 Introduction and peak use of main technologies and corresponding key references Introduction and/or peak of technology Key publications Aerial photography circa 1910s Crawford 1928; Poidebard 1929; Agache & Br´eart 1983; Brophy & Cowley 2005, Opitz & Cowley 2013, chapter 2 GIS systems circa 1980s Kvamme 1989, Allen et al. 1990, Lock 2000, Mehrer & Wescott 2005, Conolly & Lake 2006, McCoy & Ladefoged 2009, Llobera 2012 (Robotic) total station survey circa 2000s Kvamme et al. 2006 Real-time kinematic GNSS/GPS circa 2000s Barratt et al. 2000, Leckebusch 2005, Henning 2011, Limp & Barnes 2014 Object, terrestrial, and airborne laser-scanning circa 2000s Barber et al. 2001, Barber & Mills 2007, Van Genechten 2008, Vosselman & Maas 2010, Limp et al. 2011, Opitz & Cowley 2013, Remondino & Campana 2014 Photogrammetry/SfM circa 1990s and 2000s Clouten 1974, Dennett & Muessig 1980, Anderson 1982, Debevec et al. 1996, Gisiger et al. 1997, Hanke & Grussenmeyer
2002, Ioannides et al. 2014, Remondino & Campana 2014 Abbreviations: GIS, geographic information systems; GNSS, global navigation satellite system; SfM, structure from motion. 350 Opitz· Limp Much of the early and current literature relevant to archaeology can be found in conference proceedings from organizations such as CIPA (The International Committee for Documentation of Cultural Heritage) and a number of working groups from the International Society for Photogrammetry and Remote Sensing. Of particular signiﬁcance are those in Commission V: WG/2 on “Cultural Heritage Data Acquisition and Processing,” WG/3 on “Terrestrial 3D Imaging and Sensors,” and WG/5 on “Close Range Measurements for Biomedical Sciences.” (Conference proceedings are available at http://www.isprs.org/publications/default.aspx and http://cipa.icomos.org/index.php?id=28.) More recent signiﬁcant sources are the conferences and the proceedings produced by Computers and Mathematics in Archaeology (CAA; proceedings are available at http://caaconference.org/proceedings/) and the European Association for Computer Graphics’ VAST conferences (proceedings at https://diglib.eg.org/EG/DL/WS/VAST). The recent products of the EU Project 3D-COFORM (available at http://www.3d-coform.eu) and the proceedings of the recently established Digital Heritage Conferences (Addison et al. 2013) are required reading for those interested in HDSM. There are numerous recent surveys and compendia covering many of the topics discussed in this review. In particular, the reader should consider some volumes that provide excellent access points to the more widely distributed proceedings and journal articles (Ioannides et al. 2014, Opitz & Cowley 2013, Remondino & Campana 2014, Vosselman & Maas 2010). For a somewhat dated but solid review with a similar focus, see McCoy & Ladefoged (2009). As a whole, the literature on HDSM, regardless of the technology or technologies at hand, focuses on the mechanics of data capture, assessments of data quality, comparisons between data capture techniques, and case studies illustrating the successful aggregation of large quantities of data. HDSM, to date, has been primarily about data capture, with aspirations toward analysis and interpretation. However, publications that are oriented substantively toward analysis and that make the intellectual leap to archaeological interpretation and the production of new archaeological information and arguments remain rather thin. ACTIVE AREAS IN ARCHAEOLOGICAL HDSM We identify six areas of archaeological activity that explicitly or implicitly take advantage of the development of HDSM. Each of these areas, perhaps not coincidentally, is a part of the discipline where core archaeology intersects with the strong inﬂuence of an allied ﬁeld. In presenting current work and suggesting future potential in each of these areas, we intend to paint an optimistic picture of the state of HDSM in archaeology and point to a way out of the trap of data capture centrism and technology comparisons that have dominated the HDSM literature to date. We suggest that the interesting work is scattered throughout archaeology and that archaeologists using HDSM in important analytical and interpretive ways are not talking about HDSM explicitly. They are simply engaging with data on space and form and place, as archaeologists do. HDSM is most successful when it is pervasive and implicit, a state it is nearing in the work emerging in several of the key active domains identiﬁed here. Zooarchaeology and Bioarchaeology The impact of humans and their activities on animal communities, both domestic and wild, is of long-standing interest to zooarchaeologists, and the potential value of this research for studies of the evolution of phenotypes, trait selection (intentional or not), and environmental impacts viewed through animal populations has more recently been recognized by researchers interested in sustainability and ecodynamics. Well-provenanced archaeological skeletal collections are emerging www.annualreviews.org • Implications for Practice and Theory 351 (for domains outside archaeology) as key repositories for the study of medium-term evolution, leveraging time depth and spatial distribution and close ties with speciﬁc cultural behaviors, i.e., human-impacted contexts available through the archaeological record. Morphological analyses in zooarchaeology have traditionally depended on manual measurement of a few skeletal dimensions. As such, the process has been labor intensive and the suite of available metrics have been limited. Substantial advances in studies dependent on detailed morphological analysis (such as those dealing with the changes in skeletal structures relating to domestication) may be achieved through scanning and analyzing large collections of skeletons. In parallel, bioarchaeologists are taking advantage of the detailed morphological analyses supported by HDSM to pursue questions of changing skeletal morphology and biomechanics in human populations in relation to changes in
activity patterns and the environment. HDSM studies have been useful in assessing changes in skeletal structures related to the evolution of bipedalism, for example. This approach supports research on important events, including the development of bipedalism, the divergence between population groups, the emergence of agriculture, and the transition from nomadism. As with animal populations, statistical robustness in the pool of available measurements, the size of the population that may be readily addressed, and the development of new measurements relevant to biomechanical and morphological traits are facilitated through HDSM (Benazzi et al. 2014, Davies et al. 2012, Garvin & Ruff 2012, Hammond et al. 2013, Niven et al. 2009, Macintosh et al. 2014, Tocheri et al. 2005, von Cramon-Taubadel et al. 2013). The digitization of large collections by the Idaho Virtualization Laboratory (http://ivl.imnh. isu.edu/Library/VMZI/VMZI.htm), the EVAN-SOCIETY (European Virtual Anthropology Network–Society), and the Virtebra Lab at the University of West Florida (http://virtebra. wordpress.com/) are examples of key early efforts in these domains. Smaller projects handling collections for individual research or teaching are proliferating [e.g., the Museum of London Archaeology Digitized Diseases; the Paciﬁc Slope Archaeological Lab (http://oregonstate.edu/psal/); the Ikaahuk Archaeology Project; Bernard Means’s work at Virginia Commonwealth University; Appalachian State University’s teaching collection (https://osteoteaching.wordpress.com)], as digital capture of skeletal morphology moves toward the pervasive. This work is developing in parallel with efforts in paleoanthropology, e.g., the work of Ungar on dental microwear and micromorphology (Scott et al. 2006, Ungar et al. 2012). (Anthropo)geomorphology, Geoarchaeology, and Archaeological Stratigraphy The documentation of macrostratigraphy and microtopography in detail using HDSM is beginning to drive innovative work on formation and taphonomic processes, drawing on geomorphology, geoarchaeology, and stratigraphic analysis. Work in this realm is being undertaken both by geoarchaeological specialists and more broadly by excavating archaeologists documenting soil deposits in unprecedented detail. This development in documentation method is an expansion of geoarchaeology in that in the excavation context “geoarchaeology focuses on sediments and sedimentation, microstratigraphy and soil horizons, as well as evidence for alternating stability and change” (Butzer 2008, p. 404); however, most excavations are traditionally conﬁned to microstratigraphic study. Fruitful new areas identiﬁed by Butzer (2008) include the assessment of site or deposit integrity, combined human and geological processes in urban site formation, and processual links between a site and its wider environment. HDSM has a clear role to play in pursuing each of these. The question of site or deposit integrity (stratigraphic reliability) and the association of mobile ﬁnds, that is portable artifacts, with their sedimentary contexts is of fundamental importance. Detailed documentation using HDSM of the deposits’ surfaces with artifacts and inclusions 352 Opitz· Limp embedded may provide new insights to respond to this question. To date, urban excavation analyses have been dominated (in most cases) by the study of architectural remains and mobile ﬁnds. The intricate sedimentary architecture of urban sites, resulting from complex depositional histories, both during their active anthropogenic formation and use and during their afterlife, is an area with great potential. We may see substantial beneﬁts from more detailed studies of soil slumping, compaction, downslope movement, and collapse through HDSM data on surfaces and volumes. We may equally view work such as that of Lenoble & Bertran (2004) or Powlesland and the team at West Heslerton (1998, Powlesland et al. 1998, Powlesland & May 2010, Conolly & Lake 2007) as dependent on HDSM and working at the intersection of geoarchaeology and excavation because the interrelationship between site formation and taphonomic processes and artifact distributions representative of combined human and environmental impacts are studied on the basis of detailed digital mapping exercises. Indeed, the long-term research at West Heslerton led by Powlesland represents one of the key sustained investigations into plough zone stratigraphic formation processes. The detailed spatial recording of dense artifact distributions and orientations within an excavation context (general notes in Roskam 2001, pp. 150–52) is central to the study of many early human occupation sites: for example
, Haua Fteah in Libya (Douka et al. 2014); lithic scatters such as in Gault, Texas (Waters et al. 2011); and metal production sites such as in Tell Tayinat (Roames 2011). Although it is often done with total station or robotic station mapping, and less frequently with laser-scanning, this work represents an HDSM approach (Ricks 1976, McPherron 2005). These detailed object provenance studies and the study of the interﬁngering of deposits created through “natural” processes as compared with those created through more direct human intervention may allow the reﬁnement of the chain of events resulting from interactions between a site and its wider environment (Beach & Luzzadder-Beach 2008). At the same time, HDSM is acting as a driver for a fundamental change in general excavation practices. Total stations and GPS/GNSS instruments are widely used for topographic mapping on sites and have been for well over a decade, although the precision of the measurements from the commonly used differentially processed GPS/GNSS (decimeter levels at best) is modest. The increasing affordability of higher-precision (e.g., centimeter and subcentimeter level) real-time kinematic GPS/GNSS systems (cf. Limp & Barnes 2014) will undoubtedly lead to their adoption and improvement in measurements. The use of HDSM for stratigraphic recording, through either laser-scanning or SfM, is increasingly common, with leading efforts by the University of Vienna and the Ludwig Boltzmann Institute for Archaeological Prospection (LBI) (M. Doneus and W. Neubauer), Lund University and Duke University (N. Dell’Unto and M. Forte), the University of Cologne (D. Hoffmeister), the University of Michigan and the University of Arkansas (N. Terrenato and R.S. Opitz), and the Center of Interdisciplinary Science for Art, Architecture and Archaeology (CISA3) at the University of California San Diego (T.E. Levy and N. Smith) with roots in the early 2000s (Doneus & Neubauer 2005, Doneus et al. 2011, Dell’Unto et al. 2015, Forte et al. 2012, Opitz & Nowlin 2012, Smith & Levy 2014). The effect of these maturing efforts is a renewed interest in the morphology of soil deposits and the physical structure of stratigraphic sequences (e.g., Frankl et al. 2015, Kaiser et al. 2014, McCoy et al. 2010, Penasa et al. 2014, Ravanel et al. 2014); speciﬁc research questions remain to be deﬁned. The convergence of the research agendas in these linked domains should be an active area in years to come. Contextual Topography At the landscape scale, topography is being revived as a key data source in the form of contextual topography, combining microrelief representing diffuse archaeological features embedded www.annualreviews.org • Implications for Practice and Theory 353 in landforms with proxies for recent land use that provide insight into preservation and visibility (Opitz & Cowley 2013, chapter 1). Topographic data have a long history in some regions, e.g., the United Kingdom and France, where earthworks constitute an important part of the record, but this form of survey historically was and remains less well integrated into rural and regional studies in Meso-America or inland Australia, for example. This differential uptake, with the adoption of airborne lidar [also known as airborne laser-scanning (ALS)] in Europe ahead by nearly a decade compared with other regions, is tied to, among other drivers, the spread of landscape archaeology, the popularization of historic landscape characterization approaches (e.g., Dobson & Selman 2012, Rippon 2012, Turner 2006, Warnock & Grifﬁths 2014), and the ongoing (if glacially slow) implementation of the European Landscape Convention (Counc. Eur. 2000). To oversimplify, large area and holistic studies of archaeological landscapes experienced a moment of popularity in research and academic circles in concert with a growing policy interest in landscape as a unit of management at both national and European Union levels and were tied up with issues of sustainability. Thus there was impetus both from the archaeological community and from public policy institutions to investigate new methods for large-scale documentation and study, and airborne lidar/ALS was seen as a key tool for new studies and management initiatives. Well-developed and institutionally supported traditions of aerial survey were equally essential in preparing the ground for the rapid adoption of ALS into archaeological practice in the United Kingdom. A fortunate historical coincidence in the development of the European Union and its associated program of research exchange and networking programs
(e.g., Culture 2000, Archaeolandscapes) helped proliferate this approach in Europe. Further institutional drivers, including the Malta Convention (Counc. Eur. 1992), are playing a crucial role in bringing ALS into European archaeology in a heritage-management context. In the Meso-American and Southeast Asian contexts, the same ALS data affecting our understanding of rural archaeology in Europe are altering and promoting research on diffuse urbanism, with dramatic effect (see Chase et al. 2012 for a general discussion on MesoAmerica). Landmark studies including those at Ankor Wat (Evans et al. 2013) and Caracol (Chase et al. 2011) are illuminating a form of urbanism that is a far cry from the compact form often imagined when we think “city.” HDSM’s greatest successes are perhaps at this landscape scale because airborne lidar is used, if for nothing else, as a background terrain model wherever it is available. Basic assessment of lidar, wherever available, has become a standard part of desktop assessment in the United Kingdom, the Netherlands, and a growing cohort of European regions and nations in cultural and heritagemanagement contexts (Crutchley & Crow 2010 for the English Heritage perspective; GeorgesLeroy 2011 for a French Direction R´egionale des Affaires Culturelles (DRAC) perspective). For both rural and urban studies, airborne lidar has made its greatest impact in forested or otherwise heavily vegetated areas, where other forms of archaeological prospection are generally not successful [see studies in, for example, Southwest Germany (Hesse 2013); Eastern France (Fruchart 2014); Lorraine (Georges-Leroy et al. 2012); northwest Spain (Fern´andez-Lozano et al. 2014); and Italy (Coluzzi et al. 2010)]. The opening of these wooded and scrub landscapes to archaeological study provides important research opportunities, both exposing a set of activities previously not readily or thoroughly studied (archaeology of the woodlands) and generating opportunities for ﬁne-grained studies of the medium-term impacts of past anthropogenic activities on woodland vegetation communities. Persistent effects of human alterations of soils and terrain morphology are emerging from HDSM-driven studies, with implications for contemporary landscape and soils management. In both rural and dispersed or low-density urbanism contexts, the challenge now lies in going beyond the identiﬁcation of features. Airborne lidar has been used almost exclusively as a site and feature prospection tool. Creative analyses and applications for these data beyond identifying 354 Opitz· Limp Approaches HDSM materially alters the way we approach the past because it allows us to measure phenomena in what might be called the lived scale, that is a scale that has direct and immediate relevance to human behavior and experience. Archaeologists interested in how the built environment and landscapes shape social interactions and reﬂect social structures have pursued modeling, notably of lines of sight and movement, using a variety of digital tools such as GIS analyses, J-graphs, network analyses, and serious games or virtual worlds built around reconstructions (e.g., Paliou et al. 2014). Archaeologists using HDSM data are increasingly creating virtual places (e.g., Eve 2012) to stage embodied or experiential experiments. By focusing on people’s reactions to space and form, these approaches turn on themes such as movement through an environment, responses to visual cues in architecture, control of visual or physical access, or social positioning through art and monuments. The gist of the critique of these efforts, coming from the phenomenological school [e.g., McEwan & Millican 2012 and other papers in volume 19, number 4 (2012) of the Journal of Archaeological Method and Theory], is that it is impossible to reconcile a purely spatial and visual experience, or indeed any experience in a virtual setting, with the embodiment experienced in an actual landscape. Chrysanthi et al. (2012) note that computational and virtual works in archaeology “have been long haunted by ﬁerce ocularcentrism” (p. 10). This tension between the virtual experience and embodiment holds, for them, even in the case of more immersive visual and multisensory (in a limited way) virtual environments. The counterargument is that the purely visual, spatial, and metric experiences provided by HDSM in a virtual setting are a valuable complement to the full-sensory experience of being in a place. The virtual experience allows the decomposition of the visual experience as a complex phenomenon that needs to be unpacked. Moreover, the ability to quantify the visual experience, for example by measurements of eye movement or by scales of inherent visual attractiveness based on local color contrast or global rarity, being one of a kind in a set, allows for nonexperiential and nonvocabulary constrained expressions of spatial properties.
We recognize the validity of the critique but suggest that the controlled virtual environment provided by HDSM models provides an excellent medium to force ourselves to think spatially and visually through a controlled, singlesensory experience, which while highly artiﬁcial provides a useful complement to the full-blown real-world experience by pushing us into a “regime of attentiveness” (Wickstead & Barber 2012, p. 84) in which we explicitly focus our attention on a particular aspect of experience and by making us more careful observers. In studies of urban or domestic architecture, the potential for these HDSM-enabled experiential analyses, coupled with architectural analyses, is particularly important. HDSM allows the built environment to be approached both from the detailed study of the structures/plan and from the lived space using a uniﬁed platform, eliding two basic approaches to urban and domestic built environments. Thus HDSM data can afford us the ability to tack rapidly back and forth between an approach rooted in the systematic study of architecture and urban plans as the results of social processes and collective acts and the individual acting within and being guided by their built environment. Data now available for key urban sites and monumental structures should be fruitful ground www.annualreviews.org • Implications for Practice and Theory 355 for pursuing this approach: for example, Pompeii (e.g., http://www.europeana.eu/portal/ record/2048702/ISTI_CNR_HA_POMPEI_INSULA_CORNER.html and http://www. pompejiprojektet.se/insula.php),MachuPicchu(e.g.,http://cast.uark.edu/projects/internetvirtual-metrology-lab-invirmet/invirmet-data-repository/machu-picchu-3d-data.html), Scara Brae (e.g., http://www.europeana.eu/portal/record/2048712/object_HA_937.html and http://3dicons-project.eu/index.php/eng/Guidelines-Case-Studies/Case-Studies/SkaraBrae-UK),AnkorWat(e.g.,http://archive.cyark.org/3d-point-cloud-of-a-gopura-tower-inbanteay-kdei-created-from-photo-textured-laser-scan-data-media), and Skellig Michael (e.g., http://www.europeana.eu/portal/record/2048705/object_HA_839.html and http:// www.3dicons.ie/3d-content/sites/246-skelligmichaelisland#3d-model), to name just a few. Research in visual perception indicates that three-dimensional (3D) shape alone is normally enough for recognition and identiﬁcation of an object (cf. Pizlo 2010), although there are a few well-deﬁned exceptions. This potential opens an avenue for research using HDSM models and metrics that describe the spatial characteristics of something, rather than attempting to describe the total visual experience, to get at the suite of visual (and, from that, perceptual and interpretive) possibilities arising from a place. A metrics-driven approach to questions of visual and spatial experience that leverages HDSM data has the potential to bring something substantially new to this domain. The metrics used here would be separate from those geared primarily for the detailed point-to-point or curve-to-curve comparisons of two models—e.g., variants on the Hausdorff distance, which measures the distance between corresponding vertices and edges of two meshes— but rather would rely on the perceptual metrics coming out of computer vision, e.g., measures of shape complexity, curvature concentration, or global rarity (cf. Borji & Itti 2013, Wu et al. 2013). The implications of HDSM for archaeological classiﬁcation, especially at the object level, are enormous (cf. Cardillo 2010, Gilboa et al. 2013, Koutsoudis et al. 2010, Koutsoudis & Chamzas 2011, Selden et al. 2014, Sﬁkas et al. 2013). A Return to Materialism At the object scale, and at that of the built environment, HDSM is entangled with the resurgence of materialism and things as the primary means through which archaeologists engage with the world (cf. Olsen et al. 2012). In a section titled “Second Trend: A Turn to Things Themselves,” Olsen et al. (2012) notes that [r]ecently things—and thing theory—have become a fashionable subject in the cultural and social sciences. Thus, after a century of oblivion in most social and cultural research, and after decades of linguistic and textual turns, there is now much talk about a material twist: a (re)turn to things (e.g., Preda 1999; Brown 2001; Olsen 2003; Domanska 2006; Trent
mann 2009), and that, unlike previous attempts at change, the current one can count among its strengths that it is not about sacriﬁcing archaeology for something else (anthropology, philosophy, literary criticism, hard sciences, etc.)[... ]. Rather it is about having trust in our own project and in what archaeologists hold dearest: Things. It should also provide further reassurance to a few that this is not about making archaeology more theoretical, abstract, and elitist but rather an acknowledgment that knowledge and understanding also emerge from practice and mindful engagements with ditches, layers, relic walls, hearths, slab-lined pits, abandoned mining towns or last week’s rubbish. (p. 28) As the above discussion demonstrates, there is an active conversation in archaeology about things and being thing centric and what this means for us as practitioners, linking through to 356 Opitz· Limp broader discussions of things as active agents (cf. Hodder 2012). HDSM has obvious potential for foregrounding thingness, the physicality and materiality of the soils, structures, surfaces, and mobile objects. We suggest that HDSM models as direct tools for analysis (see above) and communication (see below) are a quite literal and explicit means of being more object centric and being led explicitly by material culture, an opportunity to take thingness and human-thing entanglement seriously, as archaeology’s primary means of engagement with the world. We further suggest that HDSM models are better suited to conveying thingness than are photos, charts, drawings, or other visual means of communication because models promote interactivity and engagement through an interface. Simply put, the HDSM digital model, presented in its native form through an interface that supports interaction, assumes active participatory engagement. The default mode of interaction is not static (the gaze) as with an image, but rather one in which you rotate the model, you move closer to it, you toggle its visibility, you push or pull it, you move around it. These are all descriptions of movement, of physical interaction: They are tactile, which is what makes the digital HDSM model that much closer to thingness than the image. The default mode of interaction, although seeming to be visual (we look at the models), is in fact substantially tactile and physical because, as we view, we touch and move and move through. This added level of engagement is how we interact with objects and constructions. We get to escape the gaze as the default mode of engagement, and the distancing and static nature of the gaze, which is what makes images and drawings less than ideal for communicating things as things. In this context, HDSM affords the possibility of creative means of communication and engagement with the material remains of the past. An HDSM-based model of things, mediated through an interface, provides a proxy that gives to a broad group the possibility to engage with the thing itself rather than providing a description or depiction of that thing. For archaeology, the discipline of things, the ability to communicate more directly through things as things, is the opening of an exciting and unpredictable area of study (for example, see Olson et al. 2014, Reilly & Beale 2014). Data as Publication Data publication, and the widespread use of published raw data, has languished as an ideal rarely put into practice. We most often reference the report, and even the raw data that are published are rarely reused when the report is available, the main exception to this common practice being doctoral dissertations and formal restudy projects such as the Tiber Valley Project (Patterson et al. 2000). Why are researchers reluctant to restudy or recycle other people’s data? Simply put, it is difﬁcult to understand the organization and potential pitfalls of somebody else’s data. Much of the effort surrounding metadata and ontologies and proper archiving boils down to an attempt to provide semantics and structure for disorganized and incomplete and, most importantly, uninterpreted (or in want of reinterpretation) data in an effort to ameliorate the problem stated above. HDSM products seem to be fundamentally different here because they have readily evident pseudosemantic and informational value in a raw preinterpreted state. These data are simultaneously data and representation and are readily reusable precisely because of their low semantics but legible state. It follows that HDSM may be an area for innovation in the digital reuse of data and the repeatability of analyses. With HDSM, when the digital data are curated and made available, later investigators can interrogate the data themselves, validating the initial results or, perhaps, altering them, without encountering signiﬁcant semantic or data structure barriers. With HDSM, the data recorded are more cleanly separated from the information abstracted than are data in most other research situations. Kansa (2005) has made this point clearly and emphasizes that “[s]cholarship www.annualreviews.org •
Implications for Practice and Theory 357 is better served if claims about the past can be evaluated in terms of appropriate use of evidence to support arguments and interpretations” (p. 100). This potential for reuse is being realized. A particular interesting suite of examples of digital reuse are those that utilize the Virtual Hampson Museum collection of some 400 digital objects from the pre-Columbian US mid-south (see Limp et al. 2011). The data have been accessible on the Web since 2008 under a CC 3.0 license. The materials have already been reused in numerous scholarly efforts, including those by Gilboa et al. (2013), Koutsoudis & Chamzas (2011), Koutsoudis et al. (2010), and Sﬁkas et al. (2013). In an unexpected reuse, the digital objects were used as the basis for a 2013 art installation in Toronto (Hanes 2013). The surge in publication in 3D—as evidenced by the inclusion of 3D models in traditional journal publications and in new journals that are explicitly friendly to 3D interactive content (e.g., Digital Applications in Archaeology and Cultural Heritage), as well as by the prominence of 3D in digital social media [e.g., a series of posts on the Electric Archaeology website (http://electricarchaeology.ca/); the 3D Thursday series on The Archaeology of the Mediterranean World website (https://mediterraneanworld.wordpress.com/)], by the proliferation of museum sites such as the 3D Petrie Museum (http://www.ucl.ac.uk/3dpetriemuseum), and by inclusion in major collections such as Europeana (http://www.europeana.eu/)—is motivated, on the one hand, by the foregrounding of things through the resurgence of materiality, discussed above, and, on the other hand, by the recyclability and legibility of HDSM data without intensive semantic gymnastics. Although a mix of modeled reconstructions and HDSM-derived models continues to drive publication in 3D, the HDSM models are the main force behind bringing 3D publication into the academic literature. This adaptation of publication media to accommodate HDSM 3D models, such as the move to digital publication and hyperlinked text, should be a moment for creativity and experimentation in how we communicate archaeological information and ideas. DISCUSSION AND CONCLUSIONS The domain of archaeological HDSM described here sits at the intersection of multiple disciplines. It technically draws on ﬁelds that include metrology, geomatics, surveying, computer vision, and photogrammetry, and there continues to be ongoing, relevant, signiﬁcant research in these ﬁelds. Archaeologists are rightly concerned about how these approaches will advance their study of the past, and so they are consumers of the research in these other ﬁelds. HDSM applications, then, continue the interdisciplinary trend of contemporary archaeology. Work in this domain also engages with the wider theoretical discourse, particularly with ongoing thinking regarding experiential approaches and materialism. No doubt the development of these discourses will continue to inﬂuence and, we hope, be engaged by HDSM as practiced in archaeology. The impacts of HDSM are broad, cutting across subdisciplinary divides, as the properties being measured are everywhere in archaeology, and so domain-speciﬁc impacts are many and diverse. One particularly signiﬁcant cross-cutting impact is that these methods provide multiple bridges between scientiﬁc and humanistic ways of understanding the past. Emerging approaches that combine metric analysis and experiential perspectives serve as one such bridge, and we see these as a core contribution of HDSM to new directions being forged in archaeology. Another bridge comes in the processes of analysis, interpretation, and communication of HDSM through software and hardware. HDSM data as experienced through these technologies act simultaneously as data and as illustration/visualization/virtual object. The increasing granularity of our data means that 358 Opitz· Limp the technology and user interface through which we view it becomes integral to the data itself and to how we explore and interpret it. The technology is effectively becoming a co-creator of archaeological knowledge together with the human interpreter. The second cross-cutting impact comes as HDSM allows us to decouple measurement from interpretation, data from information, leading to a fundamental alteration of the abstractive process in archaeology. Consider the common task of proﬁling a wall or mapping a ﬂoor in an excavation. The ﬁrst step is to visually process the data and abstract from it relevant objects of interest to be recorded (a pit, post mold, layer or sediment change, etc.). These abstracted elements are then recorded, usually by selecting relevant two-dimensional points and recording them on graph paper. The traditional process can be intentionally (over)simpliﬁed
to a sequence of observe, interpret/abstract, measure, record, analyze. HDSM breaks us out of this process in two ways. First, it pushes us toward a recursive and reﬂexive engagement with the data, in which we observe, record, measure, analyze, and abstract/interpret repeatedly and in varying order. Second, anyone who has followed the groundbreaking work of Simons & Chabris (1999) on “inattentional blindness” is well aware that we see only what we are prepared to see, a point discussed in an archaeological context by Barcel´o (2010, p. 93). Semiautomatic and metrics-driven analyses, promoted by HDSM simply by dint of the scale of the data, provide a parallel abstractive process, and the results of these analyses may point us to aspects of the data or information sitting in our attentional blind spots. In parallel, recent research in neurobiology, computational biology, and behavioral economics is now providing new ways of understanding how humans interact with their surroundings at a fundamental, precognitive level, opening another set of alternative analyses and offering yet another route through the abstractive process as we attempt to escape from the subconscious assumptions that we impose on the archaeological record. The third signiﬁcant cross-cutting impact is in drawing attention to space and form and careful observation and consideration of these basic archaeological dimensions. There is a gap between the ready availability of HDSM data and archaeologists with the training, abilities, and philosophical disposition to engage with the potential of the data and models derived from them, which underlies the relative lack of interpretative engagement with HDSM data sets. Similar thinking by the aerial archaeology community and the military on the need for trained observers is relevant here. From theaerialsurveyperspective,Wickstead&Barber(2012)note,“Theunique,deﬁningcharacteristic of aerial survey was not aerial photography, but the construction of a new regime of attentiveness” (pp. 84–85). It is not about the speciﬁcs of the technologies, but about an observational, analytical, and interpretive stance. Just so, the deﬁning characteristic of HDSM is not terrestrial laserscanning, SfM, or GPS/GNSS survey, but the deﬁnition of a detailed, metric approach to shape space and place. DISCLOSURE STATEMENT Within the past three years, Dr. Limp has been the recipient of NSF awards focused on advancing the utilization of spatial archaeometry methods in the international archaeological community (SBE 1321443) and 3D data acquisition and computational processing (EPS 0918970) and NEH grant funding research into 3D model publication strategies (HD-51753), and he has served as a Board Member of the National Center for Preservation Technology and Training (NCPTT). Dr. Opitz serves as the Executive Director of an NSF-funded program advancing the utilization of spatial archaeometry methods in the international archaeological community (SBE 1321443) and as a director of NEH grant funding research into 3D model publication strategies (HD-51753). www.annualreviews.org • Implications for Practice and Theory 359 LITERATURE CITED Addison AC, De Luca L, Guidi G, Pescarin S, eds. 2013. Proc. 2013 Digit. Herit. Int. Congr., Oct. 28—Nov. 1, Marseille, Fr., IEEE, Vols. I, II Adkins L, Adkins RA. 1989. Archaeological Illustration. Cambridge, UK: Cambridge Univ. Press Agache R, Br´eart B. 1983. De merveilleux jouets au service de l’arch´eologie: les ULM. Arch´eology 175:28–31 Allen KM, Green SW, Zubrow EB. 1990. Interpreting Space: GIS and Archaeology. London: Taylor & Francis Anderson RC. 1982. Photogrammetry: the pros and cons for archaeology. World Archaeol. 14(2):200–5 Barber D, Mills J. 2007. 3D Laser Scanning for Heritage: Advice and Guidance to Users on Laser Scanning in Archaeology and Architecture. London: Engl. Herit. http://www.english-heritage.org.uk/publications/ 3d-laser-scanning-for-heritage/ Barber D, Mills J, Bryan P. 2001. Laser scanning and photogrammetry: 21st century metrology. Presented at Int. Symp. CIPA, 18th, Potsdam, Ger., Herit. Doc., Proc. XVIII CIPA Symp. http://cipa.icomos.org/ index.php?id=60 Barcel´o JA. 2010. Visual analysis in archaeology. An arti�
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