CURRENT RESEARCH                      Any prospective students interested in working with me should contact me directly.


I. Human life history, demography and health

II. Ecology of sharing, cooperation and altruism

III. Social dimensions of economic decision-making

IV. Other projects


Victor fishes from canoe with bow and arrow

I. Human life history, biodemography, health and aging

The evolved human life history is unique in several fundamental aspects: 1) a long juvenile development period, 2) an exceptionally long adult lifespan, 3) support of offspring by post-reproductive individuals, 4) male subsidizing of female reproduction by food provisioning, and 5) a large brain and its capacities for learning. It is proposed that these unique features are co-evolved responses to a dietary shift towards high-quality, nutrient-dense, and difficult-to-acquire food resources. High levels of knowledge, skill, coordination, and strength are required to exploit this suite of high-quality, difficult-to-acquire resources humans consume. The attainment of those abilities requires time and a significant commitment to development. This extended learning phase during which productivity is low is compensated by higher productivity during the adult period, and subsidized by an intergenerational flow of food from old old tsimane manto young. Since productivity increases with age, the time investment in skill acquisition and knowledge leads to selection for lowered mortality rates and greater longevity, because the returns on the investments in development occur at older ages. The theoretical and empirical results obtained to date generate a series of hypotheses and new research questions this project is designed to test and answer.

  • The first objective is to advance theory in the biodemography of the human life course and test predictions regarding adult mortality and senescence. Higher "extrinsic" mortality should associate with more rapid senescence because the force of selection declines with age and any decreased probability of reaching adulthood should lead to investments in earlier reproduction and survival at the expense of somatic maintenance and repair.
  • The second objective is to test hypotheses about the roles of the brain and learning as determinants of the length of juvenile dependence and the transition to adulthood. The research will test the hypothesis that skills and knowledge are more important determinants of foraging success and horticultural productivity than strength. The research will also determine how childrearing practices and knowledge change with age and parity among women.
  • The third objective is to relate age-profiles of development and senescence in physical condition, morbidity and mortality, and behavior. One fundamental insight derived from recent theoretical and empirical results is that the timing of development co-evolves with adult mortality patterns and senescence, requiring a whole life course analysis. A second insight is that different domains of development and senescence such as physical condition, immune function, cognition and behavior co-evolve and are linked in time.
  • The fourth objective is to investigate the relationship between life history characteristics and resource flows within and among families. Foragers, especially those with large families, cannot support themselves and there is a net positive resource flow from smaller to larger families. In fact, the phase in the family lifecycle when parents are in their late forties and fifties requires net inputs from younger families and older post-reproductive individuals; thus, the long-term juvenile dependence and adolescent growth spurt could not have evolved without among-family resource flows. The research will investigate food sharing within and between families and will focus on how the adolescent growth spurt is subsidized. It will also focus on the intra-household division of labor and the allocation of tasks to individuals.
  • The fifth objective is to examine the effects of increased acculturation and integration into national society on health outcomes and the aging process.
  • The sixth objective is to stimulate collaborative comparative research on aging in a diverse array of ecological settings. No traditional society can represent the range of variation experienced by our ancestors. It is necessary to conduct comparative research to determine the universal and variable features of human life histories under traditional conditions and to investigate the effects of local conditions and integration with national society.

To date, there have been no integrated studies of development and senescence in traditional societies with little or no involvement in market economies and modern health care systems. While not living replicas of our ancestors, people in these societies are living under conditions most similar to those in existence during the long history of selection under which the human life course evolved. Our strategy is not to treat these societies as prototypes of the past, but to determine the universal and variable features of human life histories under relatively traditional conditions. This research is urgent in that this next decade will probably be the last during which research with relatively intact and isolated groups will be possible. The data collected by this research program will be an archive for future scientists who will no longer be able to obtain the information directly.

This research began in June 2002 and is still active. This research is done in collaboration with Hillard Kaplan at the University of New Mexico.

To see a map of Tsimane territory click here.


II. Ecology of sharing, cooperation and altruism

Among hunter-gatherers and many foraging-horticultural groups, there are widespread ethics of giving and stinginess is the worst social stigma. Why are social norms that emphasize generosity so common? What are their relevance for understanding human behavior? What are the social costs of being labeled stingy and do such costs have material content? In which kinds of groups are these norms more common? Food sharing has long been a topic of interest to anthropologists, but only recently have people tried to understand the functional logic behind why people share and the proximate mechanisms that guide sharing decisions. If food is costly to acquire, then shouldn't selfish individuals prosper at the expense of high producers who choose to give stuff aAnachere family eatingway? From a rational individualistic perspective, widespread food sharing is a conundrum that requires explanation. (Why was even Bill Gates pressured into giving millions of dollars away to charitable organizations?) How can we understand cross-cultural variation in sharing-based norms and behavior? Within populations, are young men more generous than, say, older men or women? Why are certain foods, such as meat, shared more widely than other foods?

Another intriguing aspect of food distribution is its relation to food production. What are the connections between the manners in which food is produced and the way it is distributed? Should a product be distributed equally, according to proportional effort, or by some other rule? Since food giving can be costly, what are the rewards to giving, and over what time span are these rewards expected? We can understand why people do things from a proximate or ultimate level. At a proximate level, Fred might give a piece of meat to Lucinda because she is crying that she has no food while he has plenty, or it's the customary thing to do. Natural selection, however, works at the ultimate level. Ultimate level explanations are probably not the ones Fred would give for why he gave Lucinda meat, but are important Ache man sharing meatnonetheless for understanding why those proximate mechanisms evolved in the first place. Does Fred give Lucinda a piece of meat because a) she is his sister and it is in his genetic self-interest to provide essential protein calories to her and her children (his nephews and neices), b) Lucinda's husband gave him a similar piece of meat last week, c) she babysat Fred's kids while he was out hunting, d) Fred hopes for sex in return, e) Lucinda's big brother, Hugo, will beat the tar out of Fred if he doesn't share, f) Lucinda will tell everyone that Fred is a stingy bastard, or g) if Fred gives it to Lucinda in front of lots of people, they might be more likely to think of him as generous. Each of these options has associated benefits, and the benefits donors may receive can fall into any one or group of these just listed.

Decisions regarding food production and distribution are important in traditional contexts, and the ability to recognize costs and benefits to different "strategies", has enormous carry-over to understanding why people do certain things in our own society that may seem costly in terms of time, money, effort, energy.

Here is a list of related and salient questions worth pondering: Why do some people join the clergy or the army? Why do many women choose to postpone reproduction until after they gradute college when peak fecundity is earlier? Why do some CEOs, managing finances with millions of dollars at stake, often conclude business deals with nothing more than an informal handshake? Why do some people donate kidneys or bone marrow? Why, if our society is so densely populated, can we still for the most part, count the number of our best, reliable friends with our fingers? Why is strong within-group unity often found within a context of discrimination or prejudice against certain other groups? If marriages are useful for contributing to the welfare of offspring (a public good), why do parents differ so much in how much time, money, energy, knowledge that they give their children? Why do many financially wealthy individuals living in isolated communities claim unhappiness, while their poorer counterparts living in tight (sometimes kin-based) communities seem more content with life? Why do extreme-sport aficionados voluntarily risk their lives in the pursuit of pleasure? Why are team sports relished so emphatically by fans who many times don't play or have any influence over the games they watch? Why did Noam Chomsky say that the U.S. has never intervened on the behalf of another nation with its main intent being humanitarian? How can non-profit organizations, promoting issues such as environmental awareness, worker solidarity, humane labor practices, more effective education, and transportation, increase donations of time and money to their organizations? These are just some of the questions with which an evolutionary perspective can provide insight.

III. Social capital, networks and reputation

The composition of social groups is of fundamental importance for the goals of economic production, resource sharing, coordination, mate choice, reputation and social status, defense, social learning and social support. Among human foragers, and especially among modern groups who mix foraging with other subsistence activities, decisions about with whom to forage or with whom to engage in other activities is one of the least studied topics in evolutionary social science. (1) Individuals may be more likely to resolve collective action problems in small self-organizing groups with an embedded history, shared understanding and trust, rather than in the more typical random mixing of 'panmictic populations' as envisioned in most theoretical models of cooperation. (2) The ways in which individuals non-randomly associate can reveal important insights about group formation. (3) The patterns of non-random interaction among group members can illuminate ways in which individuals organize into families, households, bands, and villages, and how these different levels of organization are spatially arranged in such ways as to minimize transaction costs, different forms of risk, and maximize benefits of trade, specialization, and costly signaling. (4) The structure of social networks and the role of specific individuals within those networks can reveal important aspects of status and reputation as well as insights into the transmission of beliefs and ideas.

Several research questions being are currently being investigated from this perspective. What are the characteristics of individual's sharing, kinship, and friendship networks in traditional populations of varying group sizes? How do the strength, density, size, and centrality within an individual's social network influence access to valuable information and resources, and to health and morbidity? How does the connectedness of social networks among members of a group affect individual concerns over 'what others think about you' and the importance of status in a variety of social arenas? How do individuals "create" social status over the life course, and in what ways are the accrual of social capital analgous to human capital accumulation?


IV. Other projects/affiliations

Foundations of Human Sociality

Inheritance of Inequality in Premodern Societies

Culture and the Mind Project