Human Behavioral Ecology
at the University of California, Santa Barbara
What is human behavioral ecology? Human behavioral ecology (HBE) applies the principles of evolutionary theory and optimization to the study of human behavioral diversity. Behavioral ecology examines the adaptive designs of traits, behaviors, and life histories in an ecological context. Behavioral ecology overlaps with evolutionary psychology, human or cultural ecology, and decision theory. One aim of modern human behavioural ecology is to determine how ecological and social factors influence and shape behavioral flexibility within and between populations. Among other things, HBE attempts to explain variation in behavior as adaptive solutions to the competing life-history demands of growth, development, reproduction, parental care, and mate acquisition.
CURRENT RESEARCH
I. Ecology of sharing
II. Social dimensions of economic decision-making
III. Human life history, demography and health
IV. Indigenous healthI. Ecology of sharing. Widespread ethics of 'giving' exist among many hunter-gatherers and foraging-horticultural groups, where stinginess is often touted as one of the worst social stigmas. Yet norms can vary among groups, and even within groups according to social context. Why are these norms so common in small-scale traditional societies? Do people break them, and if so, what are the consequences? What is the true social cost of being labeled stingy? In which kinds of groups are these norms more common? In many groups, we find people generously sharing portions of wild game they killed, fish they caught, tubers they extracted, fruit they gathered, or candy they bought. Food sharing has long been a topic of interest of anthropologists, but only recently have people tried to understand why people share, and the implications of such widespread giving on our understanding of what has been called a very pro-social human nature. If food is costly to acquire, then shouldn't selfish individuals prosper at the expense of high producers who choose to give stuff away? From a rational, self-interest 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?) What explains variation in amounts people give away within and between groups? Are young men more generous than, say, older men? Is meat shared more than carbohydrates? What's so special about meat?
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? (analogy: how is profit to be redistributed among firm workers that are linked in various ways to the production of the profit-generating items?) 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 nonetheless 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 seem costly in terms of fertility or survivorship. Why do some people join the clergy or the army? Why do many women choose to postpone reproduction until after college, when peak fecundity may be 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.
II. Social networks. Decision-making with regards to food production is usually modeled as a function of only the environmental constraints that describe the economic profitability of pursuing different resources, employing different technologies. The presence of other individuals matter only with respect to whether or not their labor increases food production. However, 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) are of fundamental importance for several reasons. (1) Individuals may be more likely to resolve collective action problems in small self-organizing groups rather than in the more typical panmictic group as envisioned in many 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 self-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, 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 networks 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?
III. Family dynamics, demography, and life history. View recently funded NSF proposal here 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 to 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 research program has four principal objectives. The first objective is to test predictions regarding adult mortality and senescence. The theory predicts that compared to other primates and mammals, the age-specific mortality and morbidity profiles among humans will be more "rectangular" than u-shaped. Compared to a Gompertz-like function with a smooth exponential increase in mortality during adulthood, the period of low morbidity and low mortality beginning in adolescence or early adulthood in humans will be extended and relatively flat, followed by a rapid rise in old age. 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 of the research is to acquire descriptive information on 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 these life history characteristics and resource flows within and among families. Preliminary results obtained with Ache and Hiwi foragers show that large families, especially those with teenagers as well as young children, 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. 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. Global and national forces will affect each one of these societies, but together the sample will provide the best source of information available on the traditional human life course and its variability. 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.
IV. Indigenous health. The proposed research has three broad aims. The first is to conduct an integrated study of physical growth, development, aging, health and mortality in one population, the Tsimane', a forager-horticultural society with little market involvement and access to modern health care. The second aim is to advance theory in the biodemography of the human life course, with a specific focus on aging and lifespan. The third is to lay the groundwork for collaborative, comparative research in human aging across a diverse array of ecological and social settings. The long-term goal of the research is to explain the age profile of human mortality and the rate at which humans develop and senesce in terms of economic productivity, muscular strength, endurance, body composition, disease resistance, and cognitive function.
As an initial step toward reaching that goal, the first aim is to investigate and explain features of age-specific mortality hazards and the aging process in one traditional subsistence society. Within that broad aim, our first goal is to generate a detailed description of mortality hazards and of physical and psychological function over the life course. The research is designed to answer the following questions: RQ1) what is the age-profile for mortality and how does it differ by sex? RQ2) what are the age-profiles for each major cause of death and for different forms of morbidity? RQ3) what are the age-profiles of anthropometric status, strength, endurance, psychological performance and functional abilities? Our second goal is to determine the extent to which functional decline is a unitary process and, if it is not, which declines are most closely linked to mortality hazards: RQ4) How synchronous/heterochronous are those age-profiles? RQ5) which age-profile correlates most with the age-profile of mortality? A third goal is to examine individual variation in the aging process and risks of mortality. One question concerns the causal links between functional declines and mortality hazards at the individual level: RQ6) Prospectively, what phenotypic characteristics (morbidity, co-morbidity, anthropometric status, strength, endurance, psychological performance and functional abilities) predict mortality hazards? It is also necessary to evaluate the determinants of that individual variation in rates of functional decline, especially in relation to events earlier in the lifecourse: RQ7) Do environmental assaults, such as infectious disease in childhood and adulthood, chronic parasitosis, and traumatic injury, affect the aging process and risks of mortality and morbidity later in life? Another question is the relationship between reproduction and rates of functional decline. On one hand, reproduction is expected to conflict with somatic repair and accelerate aging. On the other hand, individuals who are better able to resist environmental assaults may experience both greater reproductive success and slower aging: RQ8) Are age at first reproduction, age at last reproduction, total fertility and total surviving offspring associated positively or negatively with age-specific mortality hazards, morbidity, anthropometric status, strength, endurance, psychological performance and functional abilities? It is also possible that individual variation in the aging process is partially determined by assistance from kin: RQ9) What are the impacts of descendent kin on age-specific mortality hazards, morbidity, anthropometric status, strength, endurance, psychological performance and functional abilities?
Finally, traditional subsistence societies are undergoing dramatic change. Evaluating the effects of these historical processes on aging and mortality rates is crucial. The research is designed to measure community- and individual-level effects and to control for them in statistical analyses. We are uniquely positioned to take advantage of this variation in acculturation and market involvement to measure impacts of change: RQ10) What are the impacts of community-level characteristics (market involvement and distance from missions and towns) and individual market involvement on age-specific mortality hazards, morbidity, anthropometric status, strength, endurance, psychological performance and functional abilities?