Table of contents(19 chapters)
Altruism has long been a fundamental question motivating evolutionary approaches to behavior. Altruistic behavior is ultimately costly to the actor yet beneficial to the recipient and as such is not expected to be favored by natural selection. Its apparent commonness has led evolutionary thinkers into a wide variety of interesting areas of research, many of which are represented in this volume. Resource sharing ranks among the most basic of potentially altruistic acts. Notably absent among most other primates, humans have honed sharing to a fine art in behaviors as apparently simple as meat distributions from prey carcasses to elaborate feast making and gift giving (Mauss, 1924). Issues related to food sharing are at the center of much of the current research being done in HBE. In this volume, Frank Marlowe, Michael Gurven et al., and Bram Tucker each examine aspects of this problem.
Commonly studied hunter-gatherer traits, such as grouping and sharing, may require special attention when self-selection introduces bias into typical analyses. We therefore re-examine forager sociality by asking a series of nested questions: (1) To what extent are foraging groups random samples from the larger population? (2) What social and economic factors might explain the composition of foraging groups? (3) If certain groups of individuals preferentially forage together, do these same groups also preferentially share with each other when resident at their permanent settlement? (4) To what extent can we understand behavior in the foraging context without consideration of other contexts in which individuals live and work, and vice versa? Among the Ache of Paraguay, we show that foraging treks are not representative of the larger population, individuals vary in the kinds of treks in which they participate, and those who tend to share together at the reservation are more likely to forage together on trek.
Anthropologists commonly accept that generous food sharing is universal to small-scale subsistence populations. This paper uses observational data from a Mikea community in southwestern Madagascar to demonstrate the following: (1) Most foods are rarely shared, i.e. transferred between households; exceptions are prepared food and livestock meat; (2) Clusters of closely related households feed each other’s members reciprocally, and inconsistent with kin selection, unrelated affines are the major distributors; and (3) Tolerated theft and market value explain why livestock meat is widely shared, why scroungers are invited to share vegetal foods but rarely do, and why small game and honey are both actively defended (by hiding, theft) and scrounged (by demand sharing).
Most hypotheses proposed to explain human food sharing address motives, yet most tests of these hypotheses have measured only the patterns of food transfer. To choose between these hypotheses we need to measure people’s propensity to share. To do that, I played two games (the Ultimatum and Dictator Games) with Hadza hunter-gatherers. Despite their ubiquitous food sharing, the Hadza are less willing to share in these games than people in complex societies are. They were also less willing to share in smaller camps than larger camps. I evaluate the various food-sharing hypotheses in light of these results.
Despite the putative importance of ideological commitments in the evolution of large-scale cooperation among unrelated individuals, evolutionary researchers have yet to examine empirically the relationship between ideology and cooperation. We conduct an experimental game on Israeli kibbutz members to evaluate whether: (1) differences in ideological commitment can explain variation in cooperation within and across kibbutzim; and (2) whether certain types of ideologies are better at promoting cooperation than others. We use the cooperative behavior of Israeli city residents as a baseline and show that members of collectivized kibbutzim are more cooperative than city residents, while members of kibbutzim that have abandoned socialist ideology (privatized kibbutzim) are no more cooperative than city residents. Our results further indicate that among collectivized kibbutzim, members of religious kibbutzim are more cooperative than their secular counterparts. Religious males who engage in thrice-daily communal prayer display the highest levels of cooperation of any subpopulation in our sample. We discuss how the performance of sanctified rituals serves to internalize religious ideological commitment, thus enhancing the ability of religious ideology to motivate cooperative behavior.
LARGE-SCALE COOPERATION AMONG SUNGUSUNGU “VIGILANTES” OF TANZANIA: CONCEPTUALIZING MICRO-ECONOMIC AND INSTITUTIONAL APPROACHES
Sungusungu non-state justice organizations in Tanzania exemplify large-scale cooperation. Sungusungu third-party enforcers protect property and resolve interpersonal disputes for ethnic Sukuma and individuals from other ethnic groups who have joined the hierarchically structured organizations. We use ethnographic and experimental data to highlight the importance of institutional forces when attempting to understand patterns of large-scale cooperation. We acknowledge the usefulness of considering micro-economic theories (e.g. costly signaling theory) to understand Sungusungu, but show that social institutions and a human predisposition to act as a “strong reciprocator” are important mechanisms to explain both the origins and maintenance of Sungusungu cooperation.
DO WOMEN REALLY NEED MARITAL PARTNERS FOR SUPPORT OF THEIR REPRODUCTIVE SUCCESS? THE CASE OF THE MATRILINEAL KHASI OF N. E. INDIA
Among the Khasi, a matrilineal society in N. E. India, women have direct control over resources and help from matrilineal kin. Given this context, we question what effects husbands might have on women’s reproductive success. Multivariate analyses of husband contributions on number of live-born children, child survival, and growth of children find positive effects. These effects pertain particularly if the husband is reported to be head of household, otherwise husband effects can be negative. The analysis is framed in terms of facultative reproductive strategies as husbands’ contributions are viewed as responses to variation in women’s resources and condition.
For decades, researchers studying female genital cutting have sought to understand why the practice continues amidst abundant evidence indicating that serious health consequences can result from the more aggressive forms of cutting. Behavioral ecology theory is applied to data collected among Ghana’s Kassena-Nankana to highlight the gendered cultural forces that keep FGC practice in place through successful reproductive outcomes. With its strong association to marriageability, and thus women’s status and access to resources through marriage, circumcision has long been obligatory. However, the social transformation that is currently underway in this rural population is bringing a new perspective to the value of education, which is replacing circumcision as the resource access currency.
We examine the relationship between height and reproductive success (RS) in women from a natural fertility population in the Gambia. We observe the predicted trade-off between adult height and age at first birth: women who are tall in adulthood have later first births than short women do. However, tall women have reproductive advantages during the rest of their reproductive careers, primarily in the lower mortality rates of their children. This ultimately leads to higher fitness for taller women, despite their delayed start to reproduction. The higher RS of tall women appears to be entirely due to the physiological benefits of being tall. There is no evidence that female height is related to patterns of marriage or divorce in this population.
Data are presented on the benefits and costs that accrue to big game hunters living in the whaling community of Lamalera, Indonesia. Results indicate that big game hunting provides males a strong selective advantage. Harpooners, and to a lesser degree hunters in general, reap substantial fitness benefits from their activities. Hunters, especially harpooners, have significantly more offspring than other men after controlling for age. Hazard analysis shows that harpooners marry significantly earlier and start reproducing at an earlier age. This is not case for other hunt group members or non-hunting participants – the technicians and the boat managers. These results are consistent with data from other hunting societies that show significant reproductive benefits for good hunters. Harpooners experience other costs and benefits. Harpooners receive significantly more meat even after controlling for the effort they expend hunting, while at the same time suffer an increased risk of mortality. The results are discussed in the context of the hunting hypothesis and the current debate within human behavioral ecology concerning the role of hunting as a human male reproductive strategy.
Burden transport is a ubiquitous primate behavior. Modern humans, however, take this primate tendency and extend it to a behavioral repertoire that influences many of our daily activities and almost certainly helped shape our physical and behavioral form. I examine the transportation of food in the context of central place foraging, from the perspective of maximizing energy acquisition. A detailed model of the energetic cost of burden transport is presented and its sensitivity to the variables of body mass, burden mass, terrain, incline and velocity discussed.
This paper extends the behavioral ecology framework to predict how individuals perceive and evaluate risks. The perceptions of health and safety hazards for females, and how those perceptions relate to resource security and resource acquisition are examined. Poverty and inequality affect the constraints and opportunities available for Hispanic women working in apple packing warehouses in Eastern Washington. Warehouse workers see the health and safety risks inherent in their work and view the hazards from their positions of relative vulnerability with respect to resources. They are active agents who evaluate their situations and work to provide secure resources for themselves and their offspring within the local political and socioeconomic context.
Sex ratio theory predicts that the net investment of parents in male and female offspring should be equal in a population. Thus, if the costs and/or benefits of raising one sex to maturity differ from the other sex, then the sex ratio may deviate from 50:50. If body size and/or condition are more important to male reproductive success than it is to female reproductive success, then mothers should bias the sex ratio of their offspring in favour of males when they are in relatively good condition and are likely to produce larger offspring. Here we analyse data from a large, national survey of Ethiopian women and children to see if there is any relationship between maternal nutrition and sex ratio at birth. We find that, in rural areas, malnutrition is associated with a small but significant increase in the odds of a female birth. There is a preponderance of female births in rural areas, which may be a response to nutritional stress. However, rural mothers are more likely to cease reproduction after the birth of a son, indicating son preference. There is no evidence of either of these effects in urban areas.
EMBODIED CAPITAL AND HERITABLE WEALTH IN COMPLEX CULTURES: A CLASS-BASED ANALYSIS OF PARENTAL INVESTMENT IN URBAN SOUTH INDIA
In the recent literature in human behavioral ecology, two types of explanations have emerged as important for understanding fertility and parental investment in modern market economies: embodied capital and heritable wealth. Using this perspective, I compare the education, income, and marriage outcomes of daughters and sons among three urban south Indian social class groups that differ in terms of their education, resources, and the types of jobs they typically perform. The three class groups are found to have predictably different parental investment strategies based on their position in competitive labor markets and the investment currencies they rely on most heavily. Furthermore, I find that the currencies of both embodied capital and heritable wealth have important but separate impacts on parental investment behavior. Finally, I find that these different investment currencies may entail different investment structures, which in turn may differ by social class: in some classes, education attracts education in the marriage market and marriage expenditures help ensure a wealthy spouse, but in other classes, these currencies are substitutable.
RECONSIDERING THE COST OF CHILDBEARING: THE TIMING OF CHILDREN’S HELPING BEHAVIOR ACROSS THE LIFE CYCLE OF MAYA FAMILIES
This chapter examines the seeming paradox that although children may be a net cost to parents, they may nonetheless play a key role in underwriting the cost of large families. Maya time allocation and reproductive history data are used to approach children’s economic value from two methodological perspectives: wealth flows and the timing of children’s economic contributions. While Maya children are expensive to raise, when viewed in light of the timing of their labor supply across the demographic life cycle of the family, children’s economic contributions enable Maya parents to continue childbearing and raise more children than they might otherwise be able.
MAINTAINING THE MATRILINE: CHILDREN’S BIRTH ORDER ROLES AND EDUCATIONAL ATTAINMENT AMONG THAI KHON MÜANG
Thailand’s modernization and shift to a wage labor economy has led to increases in children’s educational attainment. This research, in two rural northern Thai villages, explores globalizing labor markets, traditional familial roles, and parental bias of educational investment by children’s gender and birth position, using a human behavioral ecology (HBE) framework. Survival models suggest that northern Thailand’s matrilineal tendencies may be increasing, not decreasing, with globalization: daughters bearing long-term expectations of support and remittance are more heavily invested in than sons, from whom matrilines expect and receive less. Birth position strongly affects educational attainment, reflecting differential familial helper and provider roles.
PATTERNS OF SHIWIAR HEALTH INSULTS INDICATE THAT PROVISIONING DURING HEALTH CRISES REDUCES JUVENILE MORTALITY
Humans lifespan is characterized by delayed maturation. Delayed maturation may arise when juvenile mortality is reduced. Recent research suggests that juvenile mortality reduction could be achieved via provisioning to weaned juveniles, particularly during health crises. Here I test this idea with data on the causes, distribution, and duration of injuries and illnesses suffered by Shiwiar forager-horticulturalists during the juvenile period. Health insults for which prolonged care is necessary for survival are a recurrent feature of the juvenile lifespan. About half the individuals for whom data on disability duration were gathered suffered health insults likely to be lethal without extended aid; over 80% were born after a parent suffered such an event; and over 90% were born after a direct ancestor in the two ascending generations suffered such an event. The data indicate that health-care provisioning reduces juvenile mortality, and that provisioning of sick and injured juveniles has important fitness consequences in this population.