Adaptive and Ecological Approaches to the Study of Hunter-Gatherers
Abstract and Keywords
Anthropology’s approach to hunter-gatherer ecology and adaptations has changed remarkably from the Enlightenment to the present. Paradigm shifts, turning on the issues of adaptive scale and the degree to which humans are subject to natural selection, have led to descriptions of hunter-gatherer adaptations as, alternately, facile and backward or elegant and forward-thinking. Modern approaches, while still varied, are far less concerned with description, focusing instead on prediction and dynamic causes of culture change, but no less convinced that a modern understanding of human adaptation requires careful study of the hunter-gatherers of the archaeological past and ethnographic present.
Hunter-gatherers are fundamental to the modern understanding of human adaptation. Indeed, a cohesive theory of human evolution and adaptation is scarcely conceivable without the information that their study has provided. Hunter-gatherers and their cultural adaptations have been alternately denigrated as simplistic in the extreme and celebrated as elegant responses to complex ecological problems. This disciplinary waffling is due both to social and political currents that influence the popular perception of hunter-gatherers, and to changing approaches to evolution and adaptation more generally, which are of course also influenced by social circumstances (Giere 1988; Kuhn 1962), as outlined in several notable works (e.g. Barnard 2000; Bettinger 1991; Bohannan and Glazer 1988; Harris 1968; 1998; Hodder 1983; 2002; Kelly 1995; McGee and Warms 2000; Willey and Sabloff 1980). Here, we are less interested in the influences than their consequences and in reviewing a broad range of approaches to the ecology and adaptations of hunter-gatherers, from the Enlightenment to the present.
While it developed quite separately from Darwinian evolutionary theory, anthropology arose as a means of answering many of the same questions, and many anthropologists have sought to explain the human condition in evolutionary terms, frequently borrowing methods from the biological sciences. It has always been clear, at the same time, that culture prevents mindless ecological interpretation of human behaviour using models developed for much simpler organisms, and the history of anthropology is, in essence, a history of wrangling over the degree to which culture sets us apart from the rest of the animal kingdom. Changing opinions on this matter are closely reflected in different anthropological approaches to hunter-gatherer ecology, hunter-gatherers being viewed as more easily dealt (p. 70) with and more intimately intertwined with the natural world than more complex societies (Bettinger 1991).
Differing approaches to hunter-gatherer adaptations and ecology reflect changing opinions in two arenas: scale of adaptation and force of environment. Decisions about scale—whether individual attributes or general behavioural propensities are more adaptively important—profoundly affect the mode of inquiry, producing distinct methodologies, each with strengths and shortcomings. Studies of larger scale (e.g. of whole cultural systems) are frequently historical accounts of individual groups, their adaptation to a particular environment and changes in that environment over time. Conversely, smaller-scale studies (e.g. of specific behaviours) are more given to cross-cultural, statistical comparison and law-like generalization, usually without reference to individual cultures. Balancing these alternative treatments of adaptation has been likened to ‘sailing a perilous course between a pseudo-explanatory reductionist atomism and stultifying non-explanatory holism’ (Mayr 1983, 329).
The influence of environment, too, has been variably interpreted; it is of little significance to some and of overwhelming importance to others. The role of culture, the premier human adaptation, is similarly contested, a product of natural selection on the one hand, insulation against selection on the other. In short, the intersection of culture with the environment remains a subject of considerable disagreement between the various strands of ecological and evolutionary explanation of human behaviour. To place modern understandings of cultural evolution and, specifically, hunter-gatherer adaptations and ecology, in a broader context, we trace the history of philosophical approaches to these issues, offering a critical review, from natural theology to neurobiology.
Speculation and Description: Adaptation Before Ecology (1600–1930)
That organisms are physically and behaviourally adapted to their environments has intrigued both lay and specialist audiences for millennia (Bettinger 1991; Burrow 1966). Seeking rational, experiential evidence of divinity, adherents to natural theology were among the first to undertake systematic studies of these adaptations, which they regarded as proof of divine creation (Paley 2006 ). This theological world view neither requires nor provides explanation of adaptive change and, prior to the late eighteenth century, there was no sense that the earth was old enough or had changed enough to require it. Environment was the unchanging scenery to which organisms were divinely and forever suited.
Charles Darwin (e.g. 1859; 1871), of course, rejected this static view, owing in part to his reading of James Hutton and Charles Lyell (1990 [1830–3]), who argued that the world was very old and constantly changing, and Thomas Malthus (1803), who argued that populations tended to grow until limited by available resources, meaning those resources would always be in short supply. An old earth, teeming with individuals in constant competition for scarce resources, gave context to Darwin’s meticulous biological fieldwork and ultimately led him to the theory of natural selection: favourable, heritable traits become more prevalent in successive generations; populations of individuals adapt (Darwin 1859; Maynard Smith 1958). (p. 71) The tenets of Darwinian evolution thrust environmental agency to the fore and, because environments change, adaptation must be treated as an ongoing process rather than a static condition (Kelly 1995).
Darwin’s (1859) allusion to human evolution in the final pages of On the origin of species sparked a crusade to classify the world’s populations into a developmental scheme (Schutkowski 2006). Biological anthropologists, grappling with ‘man’s place’ in nature, enumerated the physical differences observed among these populations and sought to identify environmental factors that might account for what they took to be the hierarchical ‘races of man’ (Huxley 1863; Rodman 1994). Early social anthropologists were similarly preoccupied with development in relation to the Enlightenment notion of progress. Herbert Spencer, the English philosopher and social theorist, was singularly influential in arguing for human progress through a hierarchy of cultural stages, selection being one of the major forces responsible for the perceived superiority of industrialized nations (Bettinger 1991; Kelly 1995; Spencer 1868). On this view, known as progressive social evolutionary theory (PSET), hunter-gatherer ‘primitives’ were developmentally retarded, wholly at the whim of nature, struggling to wrest a living from the land, and ultimately doomed to extinction at the hands of groups more advanced (Bettinger 1991; Kelly 1995; Powell 1888). This made the world’s hunter-gatherers all of a kind, their primitive stage of development eclipsing all but the most outstanding differences in technology and environment. When addressed at all, differences were attributed to contact with civilized neighbours (i.e. diffusion) or ill-defined peculiarities of environment; primitives simply lacked the mental faculties to adapt on their own (Kelly 1995; Morgan 1877). More evolutionarily advanced, ‘civilized’ folk had technology that liberated them from the uncertainties of daily food procurement, i.e. from the environment, and freed time for intellectual pursuits that were both the cause and consequence of their superiority (Bettinger 1991; Kelly 1995).
While framed in evolutionary terms, PSET differed markedly from Darwinian evolutionary theory. In particular, PSET made little room for the concept of adaption, cultures being inevitably transformed by selection, the environment serving only to hasten or slow the process to suit a particular interpretation; a harsh environment could be an obstacle that a ‘primitive’ group failed to overcome (Kelly 1995) or a challenge that fostered civilization’s ingenuity (Chinard 1947).
Although a truly modern approach to ecological adaptation was still decades off, by the turn of the twentieth century American anthropologists were taking a keener interest in the environment and its influence on culture. This is almost certainly due to circumstances peculiar to the New World. American anthropology was just beginning to form as a discipline when settlers first began pushing west into the American frontier, experiencing new, often harsh, environments. Frontier reports of encounters with living hunter-gatherers who had successfully surmounted environmental obstacles that settlers were struggling mightily to overcome made American anthropologists sensitive to the problems of environment and adaptation and kindled what would prove to be a lasting interest in hunter-gatherers (Bettinger 1991; Kelly 1995). The absence of these same circumstances in the Old World delayed the development there of anthropological interest in hunter-gatherer adaptations.
Historical particularism, the first school of American anthropological thought, reflected these sentiments in its attention to environment and its explicit recognition that hunter-gatherers, however simple, were ecologically savvy. The father of historical particularism, and of American anthropology itself, Franz Boas, was sympathetic to Darwinian (p. 72) evolution, and indeed had conducted a surprisingly sophisticated study of human phenotypic plasticity, concluding that environment had a significant effect on adaptation (Boas 1910; 1912; cf. Sparks and Jantz 2002). On the other hand, Boas staunchly opposed PSET’s unilineal view of evolution and argued that cultural similarities need not indicate parallel evolutionary development (Boas 1920; Harris 1968; Kelly 1995; McGee and Warms 2000). Boas advocated detailed field studies and appreciation of every culture on its own terms, in light of its own history and environment. As part of this agenda, Boas oversaw scores of students’ fieldwork in the US and abroad (e.g. Garfield 1931; Mead 1961 ; Radin 1923) and directed the ambitious Jesup North Pacific Expedition, which resulted in many important ethnographies on the peoples of Siberia and Alaska (Boas 1898; Bogoras 1910; Jochelson 1908; 1926; Teit 1906). Field research was key, Boas argued, and armchair generalizations would only perpetuate the wrongheaded notion of step-wise social progression.
Despite Boas’s resistance to the comparative method and universal laws of human behaviour, his intellectual progeny, Clark Wissler and Alfred Kroeber in particular, were intrigued by broad cultural patterns they observed across whole regions of the US, which they argued were more than historical happenstance. Among other things, these regional commonalities established that, in North America at least, hunter-gatherers were not homogeneous, as progressive social evolutionists had argued. Instead, they expressed a wide range of cultural manifestations (e.g. Inuit vs. Shoshone vs. Northwest Coast) that seemed more a function of environment than developmental trajectory (Bettinger 1991). Ethnographic and archaeological distributions seemed to indicate suites of cultural traits coinciding with major food resources, which were interpreted as cultural adaptations to the geographic centre of a resource’s range (Kelly 1995; Wissler 1926). These ‘culture areas’, defined according to human–resource relationships, reflect an incipient science of ecology that was taking shape in the first decades of the twentieth century. Kroeber (1939) did much to develop and publicize these patterns but cautioned that individual traits frequently and unpredictably cross-cut culture areas, obfuscating any simple relationship between culture and environment.
It is clear that, between Darwin’s Origin in 1859 and the incorporation of a formal ecological perspective around 1930, anthropology understood that the environment had an important role in shaping culture. From the mid-nineteenth to the turn of the twentieth century, speculative descriptions of cultural evolution were predicated on the notion (often implicit) that the environment was an obstacle to overcome, an impediment to progress, and a swift punisher of those who failed to keep up. Hunter-gatherers were thus closely aligned with nature, scarcely different from the rest of the animal kingdom and in the precarious position of having to adopt more sophisticated neighbours’ technologies (rather than adapt) or face extinction (Bettinger 1991). In the first decades of the twentieth century, Boas and his students were rather more explicit in their treatment of the environment, subscribing to what is termed ‘environmental possibilism’: environment poses limits, determining what is not possible, but not the form culture will take among the realm of remaining possibilities (Forde 1934; Kroeber 1939). For the possibilists, then, observed cultural traits had little to do with adaptation. Yet, the same detailed field methods and knowledge of environment that guided environmental possibilists produced a fundamentally different ecological approach in which environment was not merely limiting, but creative and enabling—producing adaptations—as Darwin had proposed nearly a century earlier (Gould 1982).
(p. 73) The Advent of an Ecological Approach to Hunter-Gatherers: Cultural Ecology and Neofunctionalism
Julian Steward believed that while the natural environment limits the range and trajectory of cultural adaptations, technology was a powerful, enabling counterbalance (Barnard 2000; Steward 1955). As the product of a particular history, technology was key to resource extraction, determining the amount of energy potentially available. Technology and all behaviours shaped by the use of technology in a particular environment, most importantly subsistence behaviour, define the ‘culture core’. Steward considered it the goal of anthropology to study the course of cultural evolution in relation to the interaction between culture core and environment (Barnard 2000; Bohannan and Glazer 1988; McGee and Warms 2000; Orlove 1980; Steward 1955).
Steward believed that understanding cultural adaptation required comparison of groups living in similar environments (McGee and Warms 2000, 226). While his Berkeley professors Kroeber and Lowie were culture area proponents, thus more willing to entertain cross-cultural studies than their mentor, Boas, they had stopped well short of exploring causal links between culture and environment, believing them too complicated to resolve at the time (Kelly 1995; Kroeber 1939). Unwilling to accept that human culture was a purely historical patchwork of accidents and connections, Steward looked cross-culturally and found recurrent cultural adaptations in similar environments, which he concluded represented general ecological adaptations (Bohannan and Glazer 1988; McGee and Warms 2000; Orlove 1980; Steward 1955).
Like the Boasians, Steward began with specific cultural behaviours in specific local environments. His most extensive archaeological and ethnographic fieldwork was in the Great Basin, where sparse, unpredictable resources and simple technology kept human population thinly spread and annually mobile, preventing the development of large, land-holding groups. The culture–environment interactions that Steward observed in the Great Basin inspired his clearest synthesis of cultural ecology in relation to what he termed the family band—small, nuclear family-centred groups that were ideally suited to small, constantly shifting resource patches. While of roughly the same size, Great Basin family bands differed fundamentally from the more familiar hunter-gatherer form of organization known as the patrilineal band, whose core components (patrilocal post-marital residence and descent, band exogamy, and communal land ownership) Steward (1936) had earlier identified as functional adaptations to a combination of environmental factors different from those of the Great Basin. He had argued that patrilineal bands arise when pedestrian hunter-gatherers armed with simple technologies occupy environments where scattered, non-migratory game constitute a major part of the diet (Steward 1936; 1955). Just as Great Basin Shoshone represented the prototypical family band, hunter-gatherers in southern Africa, the Philippines, and Australia represented Steward’s patrilineal band, their widespread distribution attesting that the core elements of this type of organization recurred regularly under similar environmental conditions (Steward 1955; Bohannan and Glazer 1988). Deviations from the basic configuration were explained as the effects of diffusion or unique local circumstances.
(p. 74) Cultural ecology was like historical particularism in its holism but not in its recognition of general principles of cultural evolution. Cultural ecologists deduced holistic ‘culture types’ from recurrent constellations of (atomistic) adaptive traits (Steward 1955); historical particularists eschewed evolutionary principles, viewing adaptation as a purely historical process of settling-in to one’s environment. Still, while cultural ecologists shared an interest in evolution via technology and energy capture with contemporary thinkers such as Leslie White (1959), their aims and approaches were worlds apart. White believed that all cultures evolved through the same broad, inevitable stages, much as Morgan (1877) and Tylor (1871) had. That Steward and the cultural ecologists took a far more empirical and particularistic tack makes their approach better suited to studies of hunter-gatherer adaptations.
Cultural ecology’s dissatisfaction with structural description and interest in functional adaptation parallels the conceptual dissatisfactions that led to evolutionary biology’s New Synthesis, also during the 1930s, when Darwinian principles of evolution were combined with Mendelian genetics (Gould 1982). In biological anthropology this meant a shift from assessing ‘man’s place’ in nature on the basis of similarities in form and structure, to taxonomies based on adaptive function. Washburn (1951, 144) wrote of the New Synthesis: ‘population genetics presents the anthropologist with a clearly formulated, experimentally verified, conceptual scheme.’ While not responding directly to these developments, Steward recognized the same potential in relation to ecological studies of culture, marking a shifting point from anthropological studies that used the language of evolution to studies that used Darwinian principles, however clumsily at first.
Cultural ecology was alternately criticized as environmental determinism and watered-down progressive social evolution. Steward anticipated the determinism charge. On his view, technology is a product of history (cultural history), not of environment. The environmental determinist agrees with Steward that behaviour is determined by the action of a given technology in a given environment, but goes on to argue that technology itself is primarily shaped by environment, which leaves no room for culture. This is why Steward argued that environment and technology had to be treated as independent ‘givens’ (Bettinger 1991; Steward 1955; 1968). Critics, of course, noted that technology was quite clearly shaped by environment. Indeed, cultural ecologists themselves tended to interpret technology not as historical accidents but as adaptive responses to environment. In the final analysis, though, Steward was right to keep technology and environment separate. We know, for example, that the Great Basin Shoshone adjusted their technology to fit local variations in environment, using finer-meshed nets for small fish, larger-meshed nets for rabbits. This variation is clearly a response to environment, made possible by a technology that permits a wide range of mesh sizes. In that sense, small-meshed nets were in the technological repertoire of the Death Valley Shoshone, even though they never brought them into play, lacking any reason for doing so, unlike the Shoshone of Elko, whose environment offered greater opportunities for fishing. When they first moved into their fish-rich environment, the Shoshone of Elko did not ‘invent’ small-meshed fishing nets, but merely applied that capability, which they had always had, as would have the Death Valley Shoshone had the opportunity arisen. What no Great Basin group had in its aboriginal technological repertoire was a mode of transportation that would have permitted them to move faster, over longer distances and in this way more effectively respond to shifting resource distributions. This changed with the introduction of the horse in the northern and eastern Great Basin, which produced major changes in diet and allowed social groups to grow much larger than (p. 75) the pre-contact family band. So Steward’s point was not that technology had no relationship to environment, but rather that every culture is limited by its technology and that those limits are not imposed by the environment but by the nature of the technology itself. Insofar as limits are concerned, technology is indeed independent of environment.
More troubling was that in emphasizing technology, cultural ecology produced a long view of cultural evolution not too different from progressive social evolutionary theory. Although Steward rejected unilineal evolution, insisting that all cultural manifestations (not merely those of hunter-gatherers) are strongly influenced by techno-environmental interactions, cultural ecology seemed to imply that as technology improved, these interactions become less influential (Orlove 1980)—precisely as progressive social evolutionary theorists had argued.
These problems aside, cultural ecology had a profound and lasting influence on anthropology. Nearly all subsequent approaches to the study of culture—and especially to the study of hunter-gatherers—drew heavily on some form of culture ecological interpretation of adaptation. This influence is perhaps most pronounced in neofunctionalism, which carried cultural ecological interpretation to an extreme in arguing that even seemingly dysfunctional cultural behaviours could be interpreted as adaptive responses to the ‘quality, quantity and distribution of resources’ (Orlove 1980, 237). Coupled with the biological view that individual behaviour needed to be understood in terms of its population-level consequences, this led neofunctionalists to interpret culture as an adaptation that functioned to maintain group homeostasis. Thus, all components of culture—all observable cultural traits—must also be adaptive. Starting from this premise, neofunctionalists quickly gravitated to cultural oddities and the ways in which they met cultural needs and contributed to group survival (Bettinger 1991).
Neofunctionalist treatments of ‘ethnographic riddles’ made for captivating reading and resulted in many detailed treatments of ecological relationships (Orlove 1980, 243). Rappaport’s (1968) work on ritual in New Guinea, Piddocke’s (1969) explanation of the Kwakiutl potlatch, and Freeman’s (1971) assessment of infanticide among the Netsilik Eskimo, for example, make functional ‘sense’ of behaviours that many Westerners find puzzling or disturbing. Warfare, excessive feasting, and infanticide are not merely rational, they turn out to be requisite for survival, maintaining population below local carrying capacity or redistributing essential resources. Interest in the regulating function of cultural behaviour reflected the neofunctionalist view that populations are the units of selection and that cultural ‘systems should tend towards homeostatic equilibrium, with populations at or close to carrying capacity; population growth above these limits induces change’ (Dow 1976; Orlove 1980, 242; Rappaport 1971a; 1971b).
Neofunctional accounts were roundly criticized in anthropology and biology alike because they rested on group rather than individual selection, consistently failed to demonstrate empirical links between purportedly functional behaviours and the need they were said to fill, and focused on the consequences rather than causes of adaptation (Bettinger 1991; Gould and Lewontin 1979; Levins and Lewontin 1985; Williams 1966).
The group selection criticism was particularly problematic. From the start, anthropological theory took whole groups or cultures as the units of analysis and explanation. This separated anthropological from biological theory until the early 1960s, when Wynne-Edwards (1962) argued that much animal behaviour increased the fitness of groups rather than individuals, which ran counter to the methodological individualism at the heart of New (p. 76) Synthetic evolutionary theory. Evolutionary biologists quickly dispatched group selection, however, demonstrating mathematically and conceptually that group selection should be exceedingly rare in nature (Price 1970; 1972; Williams 1966; Wilson 2005). Neofunctionalist explanations of culture were rejected on similar grounds. Experimental evidence (Koeslag 1997; 2003; Soltis et al. 1995) and reworking of fundamental mathematical models including Hamilton’s Rule (Bourke and Franks 1995; Trivers and Hare 1976; Wilson 2005) now suggest that group selection is likely an important evolutionary force, but this is not enough to save neofunctionalism, which suffers more fundamental flaws.
Neofunctionalists usually failed to establish causal links between behaviours of interest and the needs they are supposed to fill. For example, Piddocke (1969) argues that the seemingly extravagant and wasteful feasting that attended the Kwakiutl potlatch conceals an ingenious system for redistributing the boom and bust resources of the Northwest Coast of North America. The potlatch might have redistributed resources, but Piddocke fails to show that it actually did, that the Kwakiutl system could not survive without some level of redistribution, or that this was not accomplished by other Kwakiutl behaviours (e.g. trade, temporary resettlement, etc.: Hempel 1959; Orans 1975). Assuming a need has been correctly identified in the first place (Levins and Lewontin 1985), neofunctionalism faces the more fundamental problem of demonstrating how the trait said to satisfy that need came into being, i.e. does this or that need trigger behaviours to satisfy it (Bettinger 1991)?
Functional arguments are not inherently bad—indeed the study of adaptation is inherently functional. The view of such studies, however, has long since moved beyond static analysis of cultural oddities to work on larger adaptive systems and the more dynamic processes of adaptation and cultural change.
The New Archaeology
In the early 1960s, a crop of young US scholars became convinced, and in turn convinced many of their peers, that archaeology lacked the conceptual tools needed to tackle the problem of human adaptation and that a major overhaul of both theory and method was long overdue. These ‘new’ archaeologists were particularly interested in human–environment interactions, which had been pushed into public consciousness with the publication of works such as Rachel Carson’s Silent Spring (1962) and Paul Ehrlich’s Population Bomb (1968). The recognition in anthropology that industry and scientific ‘progress’ had a serious environmental downside promoted an increasingly neo-Malthusian view that sustainable adaptations always limited growth to levels below carrying capacity and that hunter-gatherers alone had managed this simple solution to responsible living (e.g. Lee and DeVore 1968). Understanding hunter-gatherer relationships with the earth and its resources—and whatever caused the rest of us to turn away from such an idyllic lifestyle—was intellectually stimulating and seemed socially relevant. Paradoxically, while science and scientists were no longer infallible or beyond reproach, there was a conscious effort to make the social sciences more scientific, specifically more like the biological sciences (Bettinger 1991; Orlove 1980). A scientific approach was the key plank in Lewis Binford’s (1962) platform for a revolution in archaeology, that only by testing explicit hypotheses about specific (p. 77) adaptations to specific environments could archaeologists understand the general laws, mechanisms, and processes of culture change.
This ‘New Archaeology’, or processualism, drew on Steward’s cultural ecology and biological evolutionary theory (Binford 1962; 1965; Binford and Binford 1968; Trigger 1989). Cultural ecology provided a basic framework for interpreting culture–environment interactions, biology provided the terminology and conceptual models of adaptation and selection, culture being viewed as an ‘extrasomatic means of adaptation’ (White 1959, 8). Perhaps the most important borrowing was of the ecosystems concept, which replaced the long- standing view that kept humans and nature separate with the view that humans are an integral part of environmental systems. Culture was the adaptive mechanism by which humans maintained themselves within limits imposed by carrying capacity, ensuring environmental homeostasis within a broader ecosystem (Boserup 1965; Birdsell 1968; Frisancho and Schechter 1997; Harner 1970; Kelly 1995; Laughlin and Brady 1978; Lee and DeVore 1968; Orlove 1980). That is, systems ‘seek’ to maintain equilibrium in the face of change generated by sources both internal (e.g. innovation or invention) and external (e.g. the environment), resulting in adaptation (Clarke 1968). Adaptive processes were explored in cases where change was highly visible in the archaeological record, such as tipping points from one mode of subsistence to another, e.g. from hunting and gathering to agriculture. Study of the feedback interactions between the various natural and cultural systems at work in these situations led to an understanding of fundamental adaptive processes, which could then be applied more generally to less dramatic cases of cultural change.
Archaeologists eventually realized that translating the various fragmentary components of the archaeological record into reliable interpretations of human behaviour would require a family of more modest conceptual tools that dealt with the processes that go into the formation of archaeological sites. The processes that shape living ecosystems can be directly observed; archaeologists, however, must make inferences about these processes by observing the archaeological remains of long-dead systems, frequently using ‘middle range’ models and analogues developed through ethnoarchaeological studies of living hunter-gatherers and controlled scientific observation and experimentation (Binford 1977; 1978a; 1978b; 1980; Lee and DeVore 1968; Merton 1968). Many middle range approaches—including Binford’s butchering strategy (Binford 1978b) and forager-collector models (Binford 1980), Vita-Finzi and Higgs’s (1970) site catchment analyses, and Lee’s work on calorific input-output among the !Kung (e.g. Lee 1969)—are firmly grounded in economic efficiency, which concept is also fundamental to human behavioural ecology. (For an extended discussion of Binford’s (1978b) butchering strategy model’s resemblance to optimal foraging theory, see Bettinger 1991, 107–10.) Middle Range Theory, as applied by New Archaeologists, may have anticipated human behavioural ecology’s platform, but anthropologists’ first assessments of economic efficiency were at the group level. The New Archaeology aimed to understand cultural systems holistically, but middle range necessity required reducing systems to their constituent parts, exploring their adaptations in turn. However, while Middle Range Theory helps to explain the functional connection between these parts, it is silent on how they came to be connected, i.e. what caused the adaptation or how the process leading to it should be modelled (e.g. Binford 1968). Adaptations were usually portrayed as rational, the sort of thing a group of well-informed individuals would collectively agree was a prudent course of action in the presence of a consciously perceived adaptive challenge—but no one thought anything like this actually occurred. Instead, processualists were content to describe the functional (p. 78) benefits of cultural change entailing new technologies or behaviours, leaving the mechanisms of change for others to sort out (Bettinger 1991).
As detailed by Abbott et al. (1996), Parry and Kelly (1987) provide a useful example in their analysis of the technological shift from formal to expedient cores in North America. Parry and Kelly (1987) show that as North American hunter-gatherers became less residentially mobile, they shifted from bifacial to generalized cores. Bifacial cores are more costly to produce but generate more cutting edge per unit weight, which suited the earlier, more highly mobile Palaeoindian lifestyle (Abbott et al. 1996; Kelly 1988; Parry and Kelly 1987; cf. Bamforth 2002a; Carper 2005). As mobility diminished, weight-to-cutting-edge ratio became less critical and the more costly bifacial cores increasingly fell out of use. Thus, generalized core technology is an adaptation; technology had magically adjusted to the new condition of sedentism, just as if there had been a group-level evaluation and decision about the costs and benefits of bifacial and generalized cores. In the presence of sedentism, a generalized core and flake technology may be adaptive—or may even be an adaptation. As with Piddocke and the potlatch, however, Parry and Kelly do not demonstrate this empirically, nor do they explain how the shift actually came about, merely that it did and that the result was functional. The flaw of processualism, then, was its failure to define evolutionary forces in enough detail to model the processes through which they acted.
As noted above, anthropology developed separately from Darwinian evolution and essayed quite different evolutionary explanations of culture and cultural change. The New Archaeology aspired to but did not fundamentally change this, being more philosophical, idealist, and transformational than empirical, materialist, or evolutionary (Dunnell 1980). In fact, it is only in the last three decades that anthropologists have formally applied Neo-Darwinian principles to the study of hunter-gatherers. There are at least three such approaches—human behavioural ecology, selectionist archaeology, and dual inheritance theory, which while differing in their approach to adaptation and ecology are not mutually exclusive and in many ways are complementary.
Human Behavioural Ecology
Human behavioural ecologists study the ecological relationships that shape human cultural and biological adaptations (Winterhalder and Smith 1992). This was already a topic of considerable anthropological interest when human behavioural ecology (HBE) emerged out of sociobiology in the late 1970s, but with an important difference in selective scale (Laland and Brown 2002). Behavioural ecologists wanted nothing to do with group selection, asserting instead that human behaviour is individually motivated; individuals behave in ways that maximize their own reproductive success in light of current ecological circumstances. Natural selection is said to account for this propensity (Borgerhoff Mulder 1991; Smith 1983). Behaviours change with conditions, the goal of fitness maximizing remaining constant.
(p. 79) Human behavioural ecologists quickly gravitated to optimal foraging theory as a source of ready-made models (e.g. Charnov 1976; MacArthur and Pianka 1966; Smith 1983; Stephens and Krebs 1986), and to hunter-gatherers and other simple social formations where the food quest bulked large, as logical subject matters for their application (Stephens and Krebs 1986). Optimal foraging models attracted archaeological interest because the archaeological record is frequently rich in subsistence remains, and foraging models make clear predictions about subsistence change in response to environmental variations. Using probabilistic, cost-benefit decision models and environmental data, researchers could model foraging goals, currencies, constraints, and decision-making criteria. Empirical data could be compared to model predictions to determine whether foragers were maximizing their rate of calorific return, which became the standard proxy measure for fitness (Stephens and Krebs 1986; Winterhalder and Smith 1992). In this way, human behavioural ecologists could sidestep many of the culturally motivated explanations of human behaviour that had stymied their disciplinary forebears; consciously or unconsciously, individuals seek to maximize their fitness.
Human behavioural ecologists have since broadened foraging theory by adding new model parameters or collecting new kinds of behavioural or environmental data, permitting consideration of factors initially ignored. For example, early tests, including studies of the Aché of Paraguay (Hawkes et al. 1982; Hill and Hawkes 1983), showed that living hunter-gatherers do not always maximize their rate of calorific return (Bettinger 1991; Hildebrandt and McGuire 2002; Kaplan and Hill 1992). Hill and Hawkes (1983) report that Aché men who have the most offspring often forage sub-optimally, spending more time hunting than they should, sometimes ignoring items in the ‘optimal set’ (Bamforth 2002b; Hill and Hawkes 1983; see Stephens and Krebs (1986) for a detailed description of optimal foraging models). In response, HBE broadened its theory to include myriad alternative fitness goals and currencies, including mating opportunities and prestige (Hawkes 1990; 1991; McGuire and Hildebrandt 2005), and beyond this to include non-foraging behaviours such as tool and tool stone use (Bettinger et al. 2006; Garvey 2008; 2013; Ugan et al. 2003), general life history studies (Charnov 1993; Kaplan et al. 2003), menopause (Hawkes et al. 1998; 2000; Hill and Hurtado 1991), group size (Smith 1985), birth-spacing (Blurton Jones 1986; 1987; 1997), family size (Borgerhoff Mulder 2000), polyandry (Crook and Crook 1988; Smith 1998) and the demographic transition (Borgerhoff Mulder 1998). These diverse inquiries all share the assumption that natural selection predisposed humans to behave optimally in response to environmental changes and challenges.
The increasing HBE interest in showing that outwardly ‘sub-optimal’ behaviours are in fact rational and fitness-enhancing is reminiscent of the earlier neofunctionalist agenda, but neofunctionalism and HBE are worlds apart. HBE generates empirically testable mathematical models, not ad hoc descriptions or ‘just so’ stories as some have suggested (Lyman and O’Brien 1998). Less easily dismissed is the criticism of evolutionary psychologists that HBE does not distinguish exaptations from adaptations (Symons 1987; Cosmides and Tooby 1987); exaptations happen to be beneficial for survival but were not selected in relation to that benefit, in contrast to adaptations, which were (Gould and Vrba 1982; Laland and Brown 2002). Symons (1987) argues that behavioural adaptation is the result of selective forces that act on the cognitive architecture that guides behaviour, not on the behaviours themselves. Accordingly, behaviours that promote fitness today may not have been shaped by the conditions of today, meaning that an observed correlation between a behaviour and (p. 80) reproductive success does not prove a causal connection (Laland and Brown 2002; Symons 1987). Human behavioural ecologists counter that, unlike cognitive architecture, behaviour can be directly observed, mathematically modelled, and, because it appears to be adaptive, anthropologists stand to learn a lot about human adaptability through its study (Borgerhoff Mulder et al. 1997; Grafen 1984; Laland and Brown 2002).
The evolutionary psychology criticism of HBE echoes the evolutionary biological criticism of adaptationist explanation (e.g. Williams 1966). In a pithy critique, Gould and Lewontin (1979) argue that the adaptationist propensity to recursively model a single adaptive explanation (predict > test > modify predictions > test > modify predictions,…etc.) precludes alternative evolutionary explanations. They further argue that adaptive explanation reduces an organism to a cobbled-together sum of its optimal parts (Gould and Lewontin 1979, 585). Human behavioural ecologists counter that adjusting model parameters when observations fail to meet initial expectations is what good scientists do and that critics have never offered a workable alternative. It is better to have a robust, albeit potentially flawed, method than none at all (Resnik 1997, 43). Nor does HBE apologize for its reductionist methodology; it is designed to reduce the unnumbered complexities of reality to a tractable number of abstractions (Friedman 1953, 36; Winterhalder and Smith 1992).
To illustrate the HBE approach, we return to the North American technological shift from bifacial to generalized cores. Parry and Kelly viewed this as a cost-benefit problem, explaining that, ‘the choice of expedient over formal core technology involves a trade-off between the cost of transporting tools and raw materials…and the costs of manufacturing and using tools’ (Parry and Kelly 1987, 299). HBE makes the same assumptions somewhat more formally, i.e. that the combination of behavioural plasticity and fitness optimizing should produce lithic technologies that maximize benefit relative to cost. In HBE, however, natural selection shapes the fitness behaviour of individuals (not cultures), which is simpler to model. Such a model might incorporate experimental data on the costs of manufacture and raw-material procurement, opportunity costs of production and transport, and tool use times (Beck et al. 2002; Bettinger et al. 2006; Garvey 2008; 2013; Ugan et al. 2003) leading to predictions about preferences for lithic technology at differing degrees of sedentism.
Individuals are archaeologically elusive, of course (Bamforth 2002b), but the archaeological record captures the distribution of individual behaviours, which should centre on alternatives optimal for individuals. A more difficult problem for archaeological application of HBE is whether it requires a level of environmental reconstruction beyond our present means. Optimal diet breadth, for example, can only be modelled reliably if the abundance and handling times of available resources are known (Bettinger 1991; Smith 1983). The extent of this problem and possible solutions are widely debated.
Environment also is the root of another, quite different, criticism that because a good deal of HBE research tracks behaviour in relation to environmental change, it is really just a dressed up version of environmental determinism. However, while much HBE is concerned with environmental explanation, there are many other avenues of application, as the core-to-flake example above shows. Further, Julian Steward’s argument that behaviour is as much a function of technology as environment, applies in full to HBE. In the diet breadth model, for example, resources are ranked by rate of return on handling time, which is strongly affected by technology (Broughton and O’Connell 1999, 156; Hawkes and O’Connell 1992, 63–4; cf. Lyman and O’Brien 1998). In short, that technology is a product of culture and culture history prevents characterizing HBE as environmental determinism.
(p. 81) Selectionist Archaeology
Like HBE, selectionist archaeology is less concerned with culture than with selective pressures and their product (Shennan 2008). Dunnell (1978; 1980), for example, argues that if culture is an ‘extrasomatic means of adaptation’ (White 1959, 8), the archaeological record represents the fossilized remains of human behavioural phenotypes. The New Archaeology had made similar claims, but Dunnell argued that New Archaeologists had followed an essentially non-Darwinian tack in their preoccupation with culture systems modelled as though they were living organisms (Dunnell 1980; see also Bettinger 1991). For Dunnell (1980; 1982; 1989) and a growing group of selectionists (e.g. Neff 1993; Neiman 1995; O’Brien 1996a; 1996b; Rindos 1980; Shennan 2002), evolutionary principles can and should be applied literally, rather than metaphorically, to the archaeological record. Archaeologists should focus on things that can be directly observed and measured. Human behaviour and hunter-gatherer societies do not figure prominently in this programme. The archaeological record is said to be better suited to establishing artefact lineages, determining rates of technological change, and understanding selective forces, than it is to reconstructing complex and elusive dynamic behaviours (Lyman and O’Brien 1998). That selectionist archaeology rejects behavioural explanation is surprising given how well the approach lends itself to studies of dual inheritance, which focus almost exclusively on behaviour, often referencing hunter-gatherer societies for insights (see below).
Early selectionist work argued for a ‘fundamental dichotomy’ between style and function (Dunnell 1978; 1980; O’Brien and Holland 1992). Functional attributes affect ‘fitness’, which is reflected in strongly patterned temporospatial distributions (Dunnell 1980; Maschner and Mithen 1996). Some selectionists go so far as to equate the differential persistence of artefact variants with the biological fitness of their makers (Leonard and Jones 1987); individuals who produce and use artefacts that make them better adapted to an environment live longer and produce more offspring, ensuring the persistence of the artefacts that made that possible. Neff warns, however, that while culture clearly affects survival and reproduction, there is no reason to think that the ‘contemporary design of a cultural trait is necessarily the result of past effects on biological success’ (Neff 2000, 427). This, of course, is precisely the criticism Hempel (1959) levelled against functionalist explanation.
Stylistic attributes, on the other hand, are said to be selectively neutral and thus vary randomly in frequency through time. Critics of selectionist archaeology, however, question the style–function distinction, arguing that ‘any attempt to create a rigid boundary between style and function will fail’ (Bettinger et al. 1996, 133), and that style can be functional in ways that are key to cultural evolution (Boyd and Richerson 1987; Richerson and Boyd 2005).
Of late, selectionists have become increasingly interested in interpreting the archaeological record in terms of transmission. Selectionists argue that, as extensions of the human phenotype, artefacts can be organized and analysed using the phylogenetic methods of evolutionary biology. Phylogenies and clade-diversity diagrams are used to determine evolutionary relationships between artefacts believed to share a common ancestry (e.g. Jordan and Shennan 2003; Lipo et al. 1997; O’Brien and Lyman 2003; Neiman 1995; O’Brien et al. 2001; Tehrani and Collard 2002), and are akin to artefact frequency seriations, popular during the first decades of the twentieth century (e.g. Ford 1949; Rouse 1939). Whether cultural phylogeny is susceptible to analysis using the methods of genetics is problematic, however (Eerkens et al. 2005); genetic transmission is always vertical, parent to offspring; much (p. 82) cultural transmission is horizontal between otherwise unrelated age mates as Kroeber (1963) long ago emphasized.
With reference to our North American lithic example, the archaeological selectionist (as represented in this case specifically by Abbott et al. 1996) sees core and flake technologies as competing cultural variants rather than adaptations, i.e. variants whose presence is the result of selection, which the selectionist requires be demonstrated rather than assumed, eliminating other evolutionary possibilities (mutation, drift, and sorting). Abbott and colleagues (1996) argue that the wide geographical distribution and unidirectional shift from formal to informal cores make it possible that selection favours informal cores as groups become more sedentary, but reject the Parry and Kelly (1987) argument that sedentism produced this adaptation, arguing that the presence of one behaviour (e.g. sedentism) cannot provide an evolutionary explanation for another (e.g. informal core technology). Instead, they argue that the widespread functional connection between flake technology and sedentism is a product of indirect selection or sorting. In their account, informal core technology and sedentism are functionally linked by-products of the shift from hunting and gathering to maize agriculture (Abbott et al. 1996), a highly successful adaptation to population pressure that spread widely across much of North America.
Dual Inheritance Theory (DIT)
Dual inheritance theorists look to hunter-gatherers and other simple societies to understand how cultural information changes as it is passed from person to person. They argue that while important human behaviours are the result of natural selection acting on genes, many more are acquired by cultural transmission. That is, genetic and cultural evolution interact to produce human behaviours, but cultural information is transmitted in ways that genetic information is not and thus requires a different set of interpretive tools (Bettinger et al. 1996). DIT recognizes at least four distinctive modes of cultural transmission (guided variation, and directly biased, conformist, and indirectly biased transmission). Each one entails more than simple copying, which alone carries no fitness advantage for reasons that are easy to understand. Copying saves on learning costs, but a population in which everyone copies and no one learns cannot respond to environmental change. Environmental change will thus favour learning, the frequency of which will increase until the cost of learning and the cost of copying (i.e. copying an individual with the wrong behaviour, e.g. one out of tune with the current environment) are the same—meaning that individuals who copy enjoy no selective advantage over individuals who learn, so copying confers no population level selective advantage.
Dual inheritance theory holds that the human ability to shift behaviour to optimize fitness and capacity for cultural transmission both evolved through natural selection (Ames 1996, 113). In DIT, cultural evolution is driven by natural selection acting on behavioural variation generated by individual and social learning (Bettinger et al. 1996, 134; Boyd and Richerson 1985; Campbell 1965). While accepting Neo-Darwinian methodological individualism in common with SA and HBE, i.e. that individual decisions and learning behaviour are major drivers of cultural evolution (Ames 1996; Boyd and Richerson 1985; Durham 1991; Richerson and Boyd 2005), DIT argues that important processes act at the group level and that group level phenomena (e.g. cultural transmission) strongly influence individual behaviours in ways that result in group selection (Soltis et al. 1995; Wilson and Sober 1994).
(p. 83) DIT concentrates more on the processes of cultural transmission than HBE and SA without ignoring trait-centred studies. For example, Eerkens and Lipo (2005) use computer simulation to obtain base-line values of variation generated as the result of copying error. They compare these values to measurements on projectile points from eastern California to gauge the degree and thus the source of archaeological variation. These and other methods offer archaeologists a means of discerning whether patterns observed in the archaeological record are ‘culturally or behaviourally significant or whether they are simply due to drift-like processes’ (Eerkens and Lipo 2005, 330). Eerkens et al. (2005) perform a similar modelling exercise to simulate guided variation, conformist transmission, and indirect bias. This type of modelling generates testable hypotheses of the archaeological signatures of different transmission systems (Bettinger and Eerkens 1999).
Returning to our North American lithic example for the final time, a DIT approach might begin with a trait-centred analysis of the formal–informal core transition, mapping temporospatial distributions of each core type. These data could then be compared to computer simulations of patterns generated by different transmission models, with the goal of understanding the cause of the technological shift rather than to interpret its functional outcome. Importantly, while DIT would surely weigh the selective advantages of formal and informal cores in relation to settlement mobility, it would give equal weight to the social learning mechanisms that might have persuaded individuals to choose one form over the other. The approach admits the possibility that learning biases could have caused a shift to informal cores even had they been poorly suited to the sedentary lifestyle.
Perhaps the most distinctive feature of the DIT programme is this implication that circumstances will sometimes favour cultural behaviours that are truly maladaptive. In this, it is distinct from virtually every other approach to human adaptation, which have always strived to show that all cultural behaviours, however foolish and maladaptive they may outwardly seem, are rational and adaptive when closely inspected. In contrast, dual inheritance theorists seek to understand how deleterious traits spread and why they persist even in the face of decreased fitness (Richerson and Boyd 2005; Henrich 2004).
There is a growing sense that dual inheritance theory has the potential to unite (perhaps more correctly reunite) all of the social sciences under a single explanatory framework (Gintis 2006; Laland and Brown 2002; Mesoudi et al. 2006). Importantly, the approach does not appear to lose explanatory power in the breadth of its application. DIT deals in mathematical models that permit considerable latitude for explorations at different temporal and spatial scales, making it possible to connect individual behaviours with population outcomes (Mesoudi et al. 2006). Anthropological applications have been few and archaeological applications fairly simple (i.e. distinguishing types of transmission), but this is sure to improve as continuing psychological and neurobiological studies of transmission and learning enrich our understanding and permit construction of better models.
Since Darwin’s (1859) early writings on evolution by natural selection, and especially since the New Synthesis of the 1930s, evolutionary scientists have accepted the importance of adaptation. More elegantly put, if selection leads to ‘continuous incorporation of favourable (p. 84) variation into altered forms, then evolutionary change must be fundamentally adaptive’ (Gould 1982, 381). Paradigm shifts in anthropology have turned mainly on the issue of adaptive scale and the degree to which humans are subject to natural selection. The emerging reality is that adaptation occurs at multiple levels (e.g. broad behavioural propensities, subsistence systems, individual artefacts), and there is much important work left to do in synthesizing the work that has been done at different levels, i.e. reconciling micro- and macro-evolutionary agendas. There is also the question of the underlying goal of anthropology as a discipline. Evolutionary anthropological research was for a long time descriptive, focusing on the static products of evolutionary forces and almost exclusively on aspects of culture that appear to be functional adaptations (Bettinger et al. 1996). Anthropologists have more recently shown greater interest in the dynamic causes of cultural change and, in some cases, aspects of culture that are maladaptive. In all cases, however, the trend is towards prediction and a far more robust treatment of human behaviour than simple ad hoc description (Broughton and O’Connell 1999, 154).
How much humans are subject to natural selection has been debated since at least the Enlightenment, reflecting a deep philosophical preoccupation with the problem of human free will. Hunter-gatherers have always been at the heart of this debate because they have always been taken to represent unmarred, uncomplicated examples of humankind interacting with nature, thus offering a base-line measure of human free will. Anthropologists have sought to understand how much culture insulates humans against environmental pressures by comparing modern industrial nations with their polar opposites: hunter-gatherers. Social theories most closely aligned with evolutionary biology (e.g. sociobiology and HBE) have been criticized for implying that humans are little different from the rest of the animal kingdom, driven only by the ‘instinct’ to behave rationally given the demands of environment. While purely historical explanations of culture and cultural change (e.g. Sahlins 1978) are far less deterministic, they have proven wholly unsatisfying to human evolutionists. It would seem there is a middle ground emerging in Neo-Darwinian models of human behaviour that place less emphasis on the physical than the social environment, which has increasingly moved to the fore. There is a growing recognition in human behavioural ecology, selectionist archaeology, and dual inheritance research that a truly modern theory of adaptation must incorporate modes of social learning and transmission as well as modes of subsistence, and recognize the importance of social variables (e.g. prestige) alongside environmental ones (e.g. ungulate density). This new understanding of adaptation will no doubt take shape around the hunter-gatherers of the archaeological past and ethnographic present.
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