Research Opportunities

Area 2 Projects

Emergence of inequality within human societies (Eric A. Smith) All human societies exhibit socially mediated inequalities among individuals or groups, but only relatively late in the history of our species do these inequalities assume the form of institutionalized differences in power and wealth. Smith applies evolutionary game theory and agent-based modeling to understand the emergence of such institutionalized inequalities, which emerged repeatedly both pre-agriculture (e.g., among the NW Coast Indians) and well afterwards. Although there is a large social science literature on this problem, formal models are rare. Smith’s work (with economist J.-K. Choi and archaeologist J. Boone) focuses on developing such models, both analytical (using evolutionary game theory) and computational (using agent-based simulation). To date they have developed two sets of models (Smith & Choi in press). One is based on mutually profitable exchanges between patrons (who defend resource-rich territories) and clients (who exchange services for a share of a patron’s resources). The other involves a division of labor between producers who cooperate to produce a collective good and a “manager” who enforces this cooperation (monitoring and punishing defectors) in return for a management fee, thus solving an n-player prisoner’s dilemma. The models contain demographic, economic, and environmental parameters, and involve standard replicator dynamics (which could apply equally to genetic or cultural variation) to convert strategy payoffs into population-level evolution. The eventual goal is to develop an expanded set of alternative models that can generate hypotheses to be tested empirically with archaeological and historic data. We plan to involve IPEM Fellows in several aspects of this work, from simulation model building and refinement, to empirical evaluation of alternative models and comparative analysis of human and non-human systems of inequality and their evolutionary dynamics.

Plumage color polymorphism in red-backed fairy-wrens: mechanisms and function; Ecological and social factors shaping female reproductive behavior in monogamous birds (Michael Webster) A central focus of behavioral ecology is to understand the processes that shape variation in individual reproductive strategies, but only recently have social constraints, such as those imposed by an individual's reproductive partner or other social group members, come under consideration. Webster studies reproductive conflicts of interest among group members in cooperatively breeding and socially monogamous birds. These projects examine the functional (i.e., selective forces) and mechanistic (i.e., endocrinological) bases of variable reproductive behavior. For example, female birds often copulate with males other than their social partners, and we are examining the extent to which this female reproductive tactic is limited by her social partner, by the behavior of other group members, and by kinship structure of the social group. Similarly, we seek a better functional and mechanistic understanding of why some males invest considerable energy in pursuit of copulations with females whereas others invest instead in parental care. Such questions are well-suited to analysis using the tools typically employed by anthropologists and other social scientists, such as game theory and agent-based modeling, but to date there has been limited application of such approaches. IPEM fellows will have opportunities to work on this project to develop such approaches and to empirically test the derived models, as well as to examine the suitability of conclusions for human social systems. Fellows will develop and execute their own projects that fall within the broader framework of this project, with an emphasis on developing approaches that cut across the traditional biology/anthropology division. Fellows participating in this on-going project will participate in fieldwork, most of which is conducted in Queensland, Australia in conjunction with James Cook University.

Hunting Goals and Meat Redistribution among Central African Bofi Foragers and the Archaeological Implications of Sharing (Karen Lupo) Since 1999, Lupo and colleagues have studied hunting and meat-sharing among Aka and Bofi forest foragers in the Central African Republic. They employ ethnoarchaeological methods to test models of sharing and cooperation derived from behavioral ecology. They are now examining the links between technological choices in hunting, patterns of meat-sharing, and parental effort. Observational and interview data from two forager/farmer villages identify important differences in the time-scale of decision-making and parental effort in response to local circumstances in prey availability and access to human resources. The results challenge current ideas about how resource depression influences changes in human resource choice and technology. This project has generated abundant physical samples, and their analysis may help show how, why and when some cooperative behaviors emerged in human prehistory, and how changes in habitat and prey abundance influence human choice. Their results on the time-scale and nature of decision-making bear on important contemporary issues such as (1) overexploitation of game, (2) effects of the burgeoning bush-meat trade, and (3) rainforest depletion due to rural development, especially logging. These issues are of special interest to ECOFAC (Ecosystèmes Forestiers d'Afrique Central), the EU entity managing the Ngotto Reserve. ECOFAC is helping in this work, and is using these results to augment their research on the bush-meat trade and identification of traditional tribal hunting areas. (See Hewlett's project description in Area 1 for more information on logistics and infrastructure for IPEM projects Central African Republic.)

Human Nursing Behavior (Darryl Holman) Holman and colleagues are studying the ecology of postpartum maternal-infant interactions. Beginning from a study of determinants of early breastfeeding behavior in Bangladeshi women, the team now investigates early postpartum maternal interactions in mammals generally, and how these change with different life-history traits, such as the degree of physical and neurological maturity at birth. Using phylogenetic principles and the evolution of mammalian life-history characteristics, they argue that mechanisms regulating postpartum maternal-infant interactions in relatively immature humans should be fundamentally different from those interactions in other lineages. They hypothesized that if preprogrammed early maternal behaviors are important in humans (as suggested in the psychobiology literature), they would be detected as a statistical mixture of two distributions: one reflecting preprogrammed behaviors and another reflecting culturally-mediated behavior. A second study used endocrine and questionnaire data from Bangladesh to uncover effects of pregnancy hormones on the time-to-initiation of breastfeeding (a relationship existing in other mammals). Estrogen concentrations “explained” only 4% of the variation in time-to-initiation (Holman et al. 2004). This study was the first to quantify an effect of pregnancy hormones on early postpartum behavior in humans. This group is investigating other aspects of breastfeeding behavior, and the behavioral and ecological factors leading to different lengths of lactational amenorrhea (Holman et al. in press). This work will provide research opportunities to IPEM students interested in examining both behavioral and biological components of this most primitive and obligate mammalian social behavior (breastfeeding).

Coupled Human/Ecosystems over Long Periods: Mesa Verde region ecodynamics (Tim Kohler) This team of archaeologists, hydrologists, computer scientists, a mathematician, and an economist studies the emergence of cooperation on a realistic virtual landscape representing SW Colorado between A.D. 600 and 1300. They use agent-based models of the delayed exchange of corn and of meat from hunting to determine whether reciprocal altruism can explain the changing levels of cooperation documented in the local archaeological record. This project provides a virtual lab for studying problems of the “commons” in a semi-realistic setting with abundant comparative (pre-)historical data. We can generate structured populations to study levels-of-selection problems, and compare the resultant groups with those known from archaeological data. The next phase will emphasize modeling the emergence of violence, which is especially marked on this landscape in the thirteenth-century A.D. IPEM Fellows will participate in model building, testing goodness of fit, and will gain experience with agent-based models through exposure to this research.