Bruce Winterhalder

Analyzing adaptive strategies: Human behavioral ecology at twenty-five

Human behavioral ecology (HBE) began in the mid-1970s with the application of optimal foraging models to hunter-gatherer decisions concerning resource selection and land use. In the 25 years since, the field has developed and successfully adapted evolutionary ecology theory and methods to a wide range of topics important to archaeology and to anthropology generally. In this review we examine the basic theory and its extensions to children’s foraging, conservation biology, demographic transitions, domestication and agricultural origins, the evolution of menopause, field processing and central place foraging, life history, male-female division of labor, mating tactics and fertility decisions, and resource intensification. Work on resource acquisition continues, but has been extended from foragers to pastoral and agricultural production systems. Studies of resource distribution, and especially intragroup processes of resource competition and transfers, now supplement and enrich those of resource production. Demographic and life history analyses have begun to show how ecological factors of production and distribution relate to those of mortality, fertility, and life course. Besides providing a comprehensive view of the field, we hope to demonstrate that HBE has established itself as a progressive research tradition,1 a question we take up in our conclusion. We note that this review supplements others. Two edited collections summarized the state of HBE in the early 1980s2 and early 1990s;3 shorter reviews have appeared as well.4–6 A pending collection carries us to the late 1990s.7 Reviews of HBE generally,8,9 as well as life history and demography,10–12 maturation,13 primate life span and litter size,14 mating strategies,15,16 reproductive ecology,17,18 resource transfers,19 resource conservation,20 and division of labor21 have appeared previously in this Journal. Evolutionary ecology studies “evolution and adaptive design in ecological context.”22 As a distinct field, evolutionary ecology emerged in the 1960s with the work of Charnov and Orians,23 Hutchinson,24,25 Lack,26 MacArthur and Pianka,27 MacArthur and Levins,28 MacArthur,29 Orians,30,31 and others. Textbooks on evolutionary ecology appeared in the 1970s, covering topics from the structural and behavioral traits of organisms to the organization of ecological communities. Evolutionary ecology shares fuzzy boundaries with evolutionary genetics, community ecology, animal behavior, and decision theory. When applied to the analysis of behavior, evolutionary ecology is conventionally termed “behavioral ecology.” Behavioral analyses have been an integral element of evolutionary ecology from the beginning, treating topics such as foraging strategies,27 mating systems,30 and spatial organization and competition.32 The first textbooks on behavioral ecology appeared in late 1970s33 and early 1980s.34 There now is a voluminous literature, including monograph series, dedicated journals (e.g., Evolutionary Ecology, and Behavioral Ecology and Sociobiology), and a widely read, state-of-theart series of volumes,35–38 each edition with a new set of papers. Human behavioral ecology applies evolutionary ecology models and concepts to the study of human behavioral diversity. HBE began in the mid1970s with a small set of interpretive papers39–41 and independent dissertation projects. Initially centered on foraging theory and hunter-gatherer studies, HBE has expanded over the last 25 years to encompass diverse topics and subsistence systems (Fig. 1). Although a second generation of HBE researchers is now in academic positions, the field is young enough that its initiators remain the majority of those publishing in it. HBE’s early goals were to set the cultural ecology of Steward,42 particularly as developed in his hunter-gatherer work43 and as represented in later studies such as those by Lee,44 on a sounder theoretical footing by allying it to emerging, neo-Darwinian approaches to behavior. From the start, the proposed alliance was a somewhat wary and selective one. To varying degrees, there were attempts to distance this anthropological effort (sometimes termed “socioecology”2) from the sociobiology of Wilson,45 and Bruce Winterhalder is Professor of Anthropology and Chair of the Curriculum in Ecology at University of North Carolina, Chapel Hill. He currently is working on a booklength analysis of the microecological bases of the hunter-gatherer mode of production. E-mail: winterhalder@unc.edu Eric Alden Smith is Professor of Anthropology and Director of the Graduate Program in Environmental Anthropology at University of Washington, Seattle. He is currently engaged in studies of marine foraging, reproductive strategies, and social status among Torres Strait Islanders in collaboration with Rebecca Bliege Bird and Douglas W. Bird. E-mail: easmith@u.washington.edu

Diet choice, risk, and food sharing in a stochastic environment

Abstract Foraging models can predict the optimal diet selection for an organism which has the goal of maximizing its net acquisition rate for energy while hunting and gathering. Here a simulation methodology is used to determine the optimal diet selection under the assumption that the foragers goal is to minimize the risk of an energy shortfall. The results show that the rate-maximizing and risk-minimizing diets are similar; that sharing is more effective than changes in diet in reducing risk; and that the risk-reduction which can be obtained from sharing requires quite small numbers of participants. Food sharing may be an ancient and pervasive feature of hominid foraging adaptations.

Development and Disintegration of Maya Political Systems in Response to Climate Change

Maya and Climate Climate has affected the vitality of many different societies in the past, as shown by numerous records across the globe and throughout human history. One of the most obvious and spectacular examples of this is from the Classic Maya civilization, whose advanced culture left highly detailed records of all aspects of their existence between 300 and 1000 C.E. Kennett et al. (p. 788; see the cover) present a detailed climate record derived from a stalagmite collected from a cave in Belize, in the midst of the Classic Maya settlement. The fine resolution and precise dating of the record allows changes in precipitation to be related to the politics, war, and population fluctuations of the Mayans. A record of rainfall from a stalagmite in southern Belize provides a context for better understanding Maya civilization. The role of climate change in the development and demise of Classic Maya civilization (300 to 1000 C.E.) remains controversial because of the absence of well-dated climate and archaeological sequences. We present a precisely dated subannual climate record for the past 2000 years from Yok Balum Cave, Belize. From comparison of this record with historical events compiled from well-dated stone monuments, we propose that anomalously high rainfall favored unprecedented population expansion and the proliferation of political centers between 440 and 660 C.E. This was followed by a drying trend between 660 and 1000 C.E. that triggered the balkanization of polities, increased warfare, and the asynchronous disintegration of polities, followed by population collapse in the context of an extended drought between 1020 and 1100 C.E.

Risk-Sensitive Adaptive Tactics: Models and Evidence from Subsistence Studies in Biology and Anthropology

Risk-sensitive analysis of subsistence adaptations is warranted when (i) outcomes are to some degree unpredictable and (ii) they have nonlinear consequences for fitness and/or utility. Both conditions are likely to be common among peoples studied by ecologicll anthropologists and archaeologists. We develop a general conceptual model of risk. We then review and summarize the extensive empirical literatures from biology and anthropology for methodological insights and for their comparative potential. Risk-sensitive adaptive tactics are diverse and they are taxonomically widespread. However, the anthropological literature rarely makes use of formal models of risk-sensitive adaptation, while the biological literature lacks naturalistic observations of risk-sensitive behavior. Both anthropology and biology could benefit from greater interdisciplinary exchange.

Social foraging and the behavioral ecology of intragroup resource transfers

Two chimpanzees stalk, isolate, and kill a red colobus monkey. An attendant primatologist notes that parts of the prey are relinquished selectively to onlooking scroungers (Fig. 1). A human forager returns to camp mid‐afternoon with a freshly killed, medium‐sized ungulate. Later in the day, an ethnographer observes that shared portions of the animal have found their way into the cooking pots of most or all of those in the small band. Examining a prehistoric scatter of food residues, an ethnoarcheologist wonders when early hominids began to scrounge or share food, and with what consequences for our evolution. All of these settings represent one problem: the analysis of intragroup resource transfers among social foragers. New studies in the behavioral ecology of transfers show them to be more commonplace in nature, more complicated and variable, and more subject to comparative analysis than has been appreciated.

The Population Ecology of Hunter-Gatherers and Their Prey

Abstract In this paper we combine foraging theory and population biology models to simulate dynamic relationships between hunter-gatherers and their prey resources. Hunter-gatherer population growth responds to the net marginal rate of foraging; prey population growth responds logistically to exploitation. Thus conceived, the relationship between forager and prey biomass is time-dependent and nonlinear. It changes from stable equilibrium to damped and stable cycles with modest adjustments of input parameters. And, it produces the largest sustainable human population at intermediate levels of individual work effort. At equilibrium the forager takes all prey types with a pursuit and handling rate greater than or equal to its maintenance foraging rate. The structural properties of the model compel us to reject standard anthropological interpretations of the carrying capacity concept; they provide new insights on old issues such as original affluence and intensification. Analysis of the interaction of human population, diet selection, and resource depletion requires microecological models in part because the relevant processes occur on time scales largely invisible to both ethnography and archaeology.

Environmental Analysis in Human Evolution and Adaptation Research

Human evolution and ecology analyses argue that environment is a major factor influencing biological and sociocultural adaptation, but they rarely analyze environmental properties. Multiple problems of perspective and method can arise from the normative and nondynamic environmental descriptions which pervade these analyses. This paper examines human adaptation frameworks to identify theoretical guidelines for environmental description in ways appropriate to available theories of biocultural evolution or congruent with known ecosystem qualities. Concepts and terminology are given for describing the spatial and temporal properties characteristic of ecosystems and central to hypotheses about ecological adaptation. These include: patchiness and grain; stability and resilience; persistence and recurrence; and predictability, constancy, and contingency. Field experience, theory, and the qualities of ecosystems themselves suggest that detailed, historical (long-term) environmental analysis is necessary to determine the role of ecological factors in human evolution and adapation.

A marginal model of tolerated theft

Abstract Using marginal analysis to represent Blurton Joness concept of tolerated theft, I show how equilibrium resource transfers among individuals might be affected by foraging behavior, resource qualities, and number of participants. The model applies to hominids and other species that exchange or share food or other resources. Among the results: Tolerated theft enhances the value to be derived from resources, packets intermediate in size are most likely to be subjected to tolerated theft, packet division is more likely to be unequal than equal, division is a function of group size, and tolerated theft is most likely in small groups. The model also suggests that among reciprocators the widest possible exchange or sharing is in the self-interest of the individual procuring the resource. In general, evolutionary cost-benefit accounting should track marginal changes in the value (fitness or utility) of resources. Marginal valuation is conceptually primary and may produce results that differ from direct measures of quantity.

Ecological Theory and Ethnic Differentiation Among Human Populations [and Comments and Replies]

The formation and maintenance of distinct ethnic populations within multiethnic communities is proposed to be functionally equivalent to the process of species diversification in multispecies communities. This paper suggests that while these processes operate through different selective mechanisms-one social and the other genetic-ethnic boundaries, like species boundaries, function to regulate the behavior of potentially competing populations in relation to each other and to available resources. The similarities between these two boundary-formation processes are defined and explored in an attempt to place a traditional anthropological concern within a broader theoretical perspective.

Dung as an essential resource in a highland Peruvian community

The present paper examines the use of dung for two essential human resources, fuel and fertilizer, in a highland community of southern Peru. The limited energy availability and the poor soils of the region, primarily the result of high-altitude climate and topography, necessitate this practice. Alternatives to dung use are costly or unavailable. Grazing herbivores transform the widely dispersed puna grasses into a compact and easily gathered source of energy and nutrients. Native choice among available dungs corresponds to their qualities: sheep dung, richest in nutrients, is applied as fertilizer; llama and cattle dungs, each with a high caloric value, are burned as fuels. Dung use is interpreted as an energetically efficient response to the highland environment and as central to the subsistence pattern in the area.