Showing papers in "Human Nature in 2011"

Alternatives to the Grandmother Hypothesis A Meta-Analysis of the Association Between Grandparental and Grandchild Survival in Patrilineal Populations

Abstract: We conducted a meta-analysis of 17 studies that tested for an association between grandparental survival and grandchild survival in patrilineal populations. Using two different methodologies, we found that the survival of the maternal grandmother and grandfather, but not the paternal grandmother and grandfather, was associated with decreased grandoffspring mortality. These results are consistent with the findings of psychological studies in developed countries (Coall and Hertwig Behavioral and Brain Sciences 33:1-59, 2010). When tested against the predictions of five hypotheses (confidence of paternity; grandmothering, kin proximity, grandparental senescence, and local resource competition), our meta-analysis results are most in line with the local resource competition hypothesis. In patrilineal and predominantly patrilocal societies, the grandparents who are most likely to live with the grandchildren have a less beneficial association than those who do not. We consider the extent to which these results may be influenced by the methodological limitations of the source studies, including the use of retrospective designs and inadequate controls for confounding variables such as wealth.

Getting noticed. Middle childhood in cross-cultural perspective.

Abstract: Although it is rarely named, the majority of societies in the ethnographic record demarcate a period between early childhood and adolescence. Prominent signs of demarcation are, for the first time, pronounced gender separation in fact and in role definition; increased freedom of movement for boys, while girls may be bound more tightly to their mothers; and heightened expectations for socially responsible behavior. But above all, middle childhood is about coming out of the shadows of community life and assuming a distinct, lifetime character. Naming and other rites of passage sometimes acknowledge this transition, but it is, reliably, marked by the assumption or assignment of specific chores or duties. Because the physiological changes at puberty are so much more dramatic, the transition from middle childhood is more often marked by a rite of passage than the entrance into this period. There is also an acknowledgment at the exit from middle childhood of near-adult levels of competence--as a herdsman or hunter or as gardener or infant-caretaker.

Middle childhood and modern human origins.

Abstract: The evolution of modern human life history has involved substantial changes in the overall length of the subadult period, the introduction of a novel early childhood stage, and many changes in the initiation, termination, and character of the other stages. The fossil record is explored for evidence of this evolutionary process, with a special emphasis on middle childhood, which many argue is equivalent to the juvenile stage of African apes. Although the "juvenile" and "middle childhood" stages appear to be the same from a broad comparative perspective, in that they begin with the eruption of the first molar and the achievement of the majority of adult brain size and end with sexual maturity, the detailed differences in the expression of these two stages, and how they relate to the preceding and following stages, suggest that a distinction should be maintained between them to avoid blurring subtle, but important, differences.

Adrenarche and Middle Childhood

Abstract: Middle childhood, the period from 6 to 12 years of age, is defined socially by increasing autonomy and emotional regulation, somatically by the development of anatomical structures for subsistence, and endocrinologically by adrenarche, the adrenal production of dehydroepiandrosterone (DHEA). Here I suggest that DHEA plays a key role in the coordinated development of the brain and body beginning with middle childhood, via energetic allocation. I argue that with adrenarche, increasing levels of circulating DHEA act to down-regulate the release of glucose into circulation and hence limit the supply of glucose which is needed by the brain for synaptogenesis. Furthermore, I suggest the antioxidant properties of DHEA may be important in maintaining synaptic plasticity throughout middle childhood within slow-developing areas of the cortex, including the insula, thamalus, and anterior cingulate cortex. In addition, DHEA may play a role in the development of body odor as a reliable social signal of behavioral changes associated with middle childhood.

Interhousehold Meat Sharing among Mayangna and Miskito Horticulturalists in Nicaragua

Abstract: Recent analyses of food sharing in small-scale societies indicate that reciprocal altruism maintains interhousehold food transfers, even among close kin. In this study, matrix-based regression methods are used to test the explanatory power of reciprocal altruism, kin selection, and tolerated scrounging. In a network of 35 households in Nicaragua’s Bosawas Reserve, the significant predictors of food sharing include kinship, interhousehold distance, and reciprocity. In particular, resources tend to flow from households with relatively more meat to closely related households with little, as predicted by kin selection. This generalization is especially true of household dyads with mother-offspring relationships, which suggests that studies of food sharing may benefit from distinctions between lineal and collateral kin. Overall, this analysis suggests that exchanges among kin are primarily associated with differences in need, not reciprocity. Finally, although large game is distributed widely, qualitative observations indicate that hunters typically do not relinquish control of the distribution in ways predicted by costly signaling theory.

Female Mobility and Postmarital Kin Access in a Patrilocal Society

Abstract: Across a wide variety of cultural settings, kin have been shown to play an important role in promoting women’s reproductive success. Patrilocal postmarital residence is a potential hindrance to maintaining these support networks, raising the question: how do women preserve and foster relationships with their natal kin when propinquity is disrupted? Using census and interview data from the Himba, a group of semi-nomadic African pastoralists, I first show that although women have reduced kin propinquity after marriage, more than half of married women are visiting with their kin at a given time. Mobility recall data further show that married women travel more than unmarried women, and that women consistently return to stay with kin around the time of giving birth. Divorce and death of a spouse also trigger a return to living with kin, leading to a cumulative pattern of kin coresidence across the lifespan. These data suggest that patrilocality may be less of a constraint on female kin support than has been previously assumed.

Postmarital residence and bilateral kin associations among hunter-gatherers: Pumé foragers living in the best of both worlds.

Abstract: Dispersal of individuals from their natal communities at sexual maturity is an important determinant of kin association. In this paper we compare postmarital residence patterns among Pume foragers of Venezuela to investigate the prevalence of sex-biased vs. bilateral residence. This study complements cross-cultural overviews by examining postmarital kin association in relation to individual, longitudinal data on residence within a forager society. Based on cultural norms, the Pume have been characterized as matrilocal. Analysis of Pume marriages over a 25-year period finds a predominant pattern of natalocal residence. We emphasize that natalocality, bilocality, and multilocality accomplish similar ends in maximizing bilateral kin affiliations in contrast to sex-biased residential patterns. Bilateral kin association may be especially important in foraging economies where subsistence activities change throughout the year and large kin networks permit greater potential flexibility in residential mobility.

Evolutionary Contributions to Solving the “Matrilineal Puzzle”

Abstract: Matriliny has long been debated by anthropologists positing either its primitive or its puzzling nature. More recently, evolutionary anthropologists have attempted to recast matriliny as an adaptive solution to modern social and ecological environments, tying together much of what was known to be associated with matriliny. This paper briefly reviews the major anthropological currents in studies of matriliny and discusses the contribution of evolutionary anthropology to this body of literature. It discusses the utility of an evolutionary framework in the context of the first independent test of Holden et al.’s 2003 model of matriliny as daughter-biased investment. It finds that historical daughter-biased transmission of land among the Mosuo is consistent with the model, whereas current income transmission is not. In both cases, resources had equivalent impacts on male and female reproduction, a result which predicts daughter-biased resource transmission given any nonzero level of paternity uncertainty. However, whereas land was transmitted traditionally to daughters, income today is invested in both sexes. Possible reasons for this discrepancy are discussed.

The Rebirth of Kinship

Abstract: Kinship was one of the key areas of research interest among anthropologists in the nineteenth century, one of the most hotly debated areas of theory in the early and mid-twentieth century, and yet an area of waning interest by the end of the twentieth century. Since then, the study of kinship has experienced a revitalization, with concomitant disputes over how best to proceed. This special issue brings together recent studies of kinship by scientific anthropologists employing evolutionary theory and quantitative methods. We argue that the melding of the evolutionary theoretical perspective with quantitative and ethnographic methodologies has strengthened and reinvigorated the study of kinship by synthesizing and extending existing research via rigorous analyses of evidence.

Juvenile Subsistence Effort, Activity Levels, and Growth Patterns

Abstract: Attention has been given to cross-cultural differences in adolescent growth, but far less is known about developmental variability during juvenility (ages 3-10) Previous research among the Pume, a group of South American foragers, found that girls achieve a greater proportion of their adult stature during juvenility compared with normative growth expectations To explain rapid juvenile growth, in this paper we consider girls' activity levels and energy expended in subsistence effort Results show that Pume girls spend far less time in subsistence tasks in proportion to their body size compared with adults, and they have lower physical activity levels compared with many juveniles cross-culturally Low activity levels help to explain where the extra energy comes from to support rapid growth in a challenging environment We suggest that activity levels are important to account for the variation of resource and labor transfers in mediating energy availability

Kin preference and partner choice: patrilineal descent and biological kinship in Lamaleran cooperative relationships.

Abstract: This paper presents a comparison of social kinship (patrilineage) and biological kinship (genetic relatedness) in predicting cooperative relationships in two different economic contexts in the fishing and whaling village of Lamalera, Indonesia. A previous analysis (Alvard, Human Nature 14:129–163, 2003) of boat crew affiliation data collected in the village in 1999 found that social kinship (patrilineage) was a better predictor of crew affiliation than was genetic kinship. A replication of this analysis using similar data collected in 2006 finds the same pattern: lineage is a better predictor than genetic kinship of crew affiliation, and the two together explain little additional variance over that explained by lineage alone. However, an analogous test on food-sharing relationships finds the opposite pattern: biological kinship is a better predictor of food-sharing relationships than is social kinship. The difference between these two cooperative contexts is interpreted in terms of kin preferences that shape partner choice, and the relative autonomy with which individuals can seek to satisfy those preferences. Drawing on stable matching theory, it is suggested that unilineal descent may serve as a stable compromise among multiple individuals’ incongruent partner preferences, with patriliny favored over matriliny in the crew-formation context because it leads to higher mean degrees of relatedness among male cooperators. In the context of food-sharing, kin preferences can be pursued relatively autonomously, without the necessity of coordinating preferences with those of other households through the institution of lineage.

The place of proximity: social support in mother-adult daughter relationships.

Abstract: The mother–adult daughter relationship has been highlighted in both the social sciences and the public health literature as an important facet of social support networks, particularly as they pertain to maternal and child health. Evolutionary anthropologists also have shown positive associations between support from maternal grandmothers and various outcomes related to reproductive success; however, many of these studies rely on proximity as a surrogate measure of support. Here I present data from the Puerto Rican Maternal and Infant Health Survey (PRMIHS) comparing geographic proximity of mother and daughter with a self-reported measure of mother-to-daughter support. These two measures were used to predict infant health outcomes as well as various measures of instrumental and emotional aid provided during pregnancy and after birth. Primary support was shown to have a positive effect across the analyses, whereas geographic proximity was associated with an increased risk of infant mortality and low birth weight as well as reduced odds of receiving support. This paradox was then examined using a combination variable that teased out the interactions of maternal support and proximity. Women who were geographically close to their mothers but who did not consider them a primary source of support had increased odds of infant death and low birth weight, and were less likely to receive either tangible or intangible forms of aid, while women whose mothers were both close and primary showed uniformly positive outcomes. These results place the role of propinquity within the larger context of social support and highlight the need for more detailed studies of social support within evolutionary anthropology.

Dynamics of Postmarital Residence among the Hadza A Kin Investment Model

Abstract: When we have asked Hadza whether married couples should live with the family of the wife (uxorilocally) or the family of the husband (virilocally), we are often told that young couples should spend the first years of a marriage living with the wife’s family, and then later, after a few children have been born, the couple has more freedom—they can continue to reside with the wife’s kin, or else they could join the husband’s kin, or perhaps live in a camp where there are no close kin. In this paper, we address why shifts in kin coresidence patterns may arise in the later years of a marriage, after the birth of children. To do so, we model the inclusive fitness costs that wives might experience from leaving their own kin and joining their husband’s kin as a function of the number of children in their nuclear family. Our model suggests that such shifts should become less costly to wives as their families grow. This simple model may help explain some of the dynamics of postmarital residence among the Hadza and offer insight into the dynamics of multilocal residence, the most prevalent form of postmarital residence among foragers.

Darkness’s Descent on the American Anthropological Association

Abstract: In September 2000, the self-styled “anthropological journalist” Patrick Tierney began to make public his work claiming that the Yanomamo people of South America had been actively—indeed brutally—harmed by the sociobiological anthropologist Napoleon Chagnon and the geneticist-physician James Neel. Following a florid summary of Tierney’s claims by the anthropologists Terence Turner and Leslie Sponsel, the American Anthropological Association (AAA) saw fit to take Tierney’s claims seriously by conducting a major investigation into the matter. This paper focuses on the AAA’s problematic actions in this case but also provides previously unpublished information on Tierney’s falsehoods. The work presented is based on a year of research by a historian of medicine and science. The author intends the work to function as a cautionary tale to scholarly associations, which have the challenging duty of protecting scholarship and scholars from baseless and sensationalistic charges in the era of the Internet and twenty-four-hour news cycles.

The matrilocal tribe: an organization of demic expansion.

Abstract: This article integrates (1) research in the historical dynamics of state societies relating group solidarity and group expansion to cultural frontiers, (2) comparative research in anthropology relating matrilocality to a particular variety of internal politics and a particular form of warfare, and (3) interdisciplinary reconstructions of large-scale “demic expansions” and associated kinship systems in prehistory. The argument is that “metaethnic frontiers,” where very different cultures clash, are centers for the formation of larger, more enduring, and more militarily effective groups. In small-scale non-state societies, the major path toward the formation of such groups is the establishment of cross-cutting ties among men. This often involves the adoption of matrilocal norms. The current distribution of matrilocality and matrilineality around the world may be partly a residue of major demic expansions in prehistory involving matrilocal tribes. This hypothesis is evaluated with a range of evidence, including information regarding the spread of two language families, Bantu and Austronesian.

Has the child welfare profession discovered nepotistic biases

Abstract: A major trend in foster care in developed countries over the past quarter century has been a shift toward placing children with "kin" rather than with unrelated foster parents. This change in practice is widely backed by legislation and is routinely justified as being in the best interests of the child. It is tempting to interpret this change as indicating that the child welfare profession has belatedly discovered that human social sentiments are nepotistic in their design, such that kin tend to be the most nurturant alloparents. Arguably, however, the change in practice has been driven by demographic, economic, and political forces rather than by discovery of its benefits. More and better research is needed before we can be sure that children have actually benefitted.

Genetic and Cultural Kinship among the Lamaleran Whale Hunters

Abstract: The human ability to form large, coordinated groups is among our most impressive social adaptations. Larger groups facilitate synergistic economies of scale for cooperative breeding, such economic tasks as group hunting, and success in conflict with other groups. In many organisms, genetic relationships provide the structure for sociality to evolve via the process of kin selection, and this is the case, to a certain extent, for humans. But assortment by genetic affiliation is not the only mechanism that can bring people together. Affinity based on symbolically mediated and socially constructed identity, or cultural kinship, structures much of human ultrasociality. This paper examines how genetic kinship and two kinds of cultural kinship—affinal kinship and descent—structure the network of cooperating whale hunters in the village of Lamalera, Indonesia. Social network analyses show that each mechanism of assortment produces characteristic networks of different sizes, each more or less conducive to the task of hunting whales. Assortment via close genetic kin relationships (r = 0.5) produces a smaller, denser network. Assortment via less-close kin relations (r = 0.125) produces a larger but less dense network. Affinal networks are small and diffuse; lineage networks are larger, discrete, and very dense. The roles that genetic and cultural kinship play for structuring human sociality is discussed in the context of these results.

The foundation of kinship: households.

Abstract: Men’s hunting has dominated the discourse on energy capture and flow in the past decade or so. We turn to women’s roles as critical to household formation, pair-bonding, and intergenerational bonds. Their pivotal contributions in food processing and distribution likely promoted kinship, both genetic and affinal, and appear to be the foundation from which households evolved. With conscious recognition of household social units, variable cultural constructions of human kinship systems that were sensitive to environmental and technological conditions could emerge. Kinship dramatically altered the organization of resource access for our species, creating what we term “kinship ecologies.” We present simple mathematical models to show how hunting leads to dependence on women’s contributions, bonds men to women, and bonds generations together. Kinship, as it organized transfers of food and labor energy centered on women, also became integrated with the biological evolution of human reproduction and life history.

Statement on the publication of Alice Dreger's investigation, Darkness's descent on the American Anthropological Association: a cautionary tale.

Abstract: We feel it is important to explain to the readership of Human Nature why we decided to break with our tradition of publishing only those papers based on evolutionary approaches to human behavior that are highly empirical in terms of substantive testing of theoretical predictions with data. Our decision to publish an investigation of the conduct of a professional society needs to be explained to those who are not aware of the history that lies behind it. Although the readers of Human Nature come from a wide variety of disciplines, a solid core of both readers and Consulting Editors identify themselves as Evolutionary Anthropologists or Human Evolutionary Ecologists, do research in nonindustrialized societies, and practice scientific methodology. This is the group that was most damaged in reputation and status by the original publication in 2001 of Darkness in El Dorado by Patrick Tierney (New York: W. W. Norton) and, that same year, by the President and Executive Board of the American Anthropological Association, who launched an unstructured investigation into accusations of scientifically motivated genocide against James Neel, a geneticist, and Napoleon Chagnon, an anthropologist. Evolutionary anthropologists were very disturbed by what seemed to be a witchhunting psychology that rippled through the AAA meetings, the AAA-sponsored investigation, and subsequent web postings. A number of us decided that we needed Hum Nat DOI 10.1007/s12110-011-9106-8

Life history of female preferences for male faces: a comparison of pubescent girls, nonpregnant and pregnant young women, and middle-aged women.

Abstract: Although scientific interest in facial attractiveness has developed substantially in recent years, few studies have contributed to our understanding of the ontogeny of facial preferences. In this study, attractiveness of 30 male faces was evaluated by four female groups: girls at puberty, nonpregnant and pregnant young women, and middle-aged women. The main findings are as follows: (1) Preference for sexy-looking faces was strongest in young, nonpregnant women. (2) Biologically more mature girls displayed more adultlike preferences. (3) The intragroup consistency for postmenopausal women was relatively low. (4) In terms of the preference pattern, pregnant women were more similar to perimenopausal women than they were to their nonpregnant peers. (5) Preference for youthful appearance decreased with the age of the women. I argue that the life history of female preferences for male faces is, to a large extent, hormone-driven and underpinned by a set of evolutionary adaptations.

An introduction to the special issue on middle childhood.

Abstract: Middle childhood is recognized by developmental psychologists as a distinct developmental stage between early childhood and adolescence, defined by increasing cognitive development, emotional regulation, and relative social independence. Adults have increasing expectations of children during middle childhood, as reflected in Sheldon’s White’s (1996) description of this stage as “the age of reason and responsibility.” Developmentally, the onset of middle childhood is defined by Piaget’s (1963) “5 to 7 transition,” with the end marked by the onset of puberty. Middle childhood is generally associated with importance of and identification with same-sex groups, thus providing a basis for Freud’s notion of a latency period during childhood. From an evolutionary perspective, middle childhood is consistent with what biologists have referred to as the “juvenile phase” (for primates, see Pereira and Fairbanks 2002), when individuals who are not yet reproductively capable are responsible for feeding themselves but are still under the social influence of their parents. Although the dramatic physical changes associated with puberty provide a clear basis for understanding the end of middle childhood, the biological (both somatic or neurological) underpinnings of the 5-to-7 transition have remained obscure until quite recently, leaving the universal nature of middle childhood in doubt. Recent findings of the onset of cortical maturation starting around age 6 (Gogtay et al. 2004) suggests that the 5-to-7 transition is closely related to the timing of brain development. The loss of juvenile teeth and the onset of adrenarche (increase in the adrenal production of the neurosteroid DHEAS) at about the same time index somatic changes associated with the transition. Thus, middle childhood in humans Hum Nat (2011) 22:247–248 DOI 10.1007/s12110-011-9118-4

Urbanization and daughter-biased parental investment in Fiji.

Abstract: Parental investment decisions guide parental actions regarding children’s productive work and are shaped by ecological context. Urban ecology enhances long-term payoffs to investment in human capital, increasing opportunity costs for work performed by children, and decreased workload should result. Using an embodied capital framework, self-reported data on urban and rural Indo-Fijian children’s work activities are compared. Results show higher workloads for older children, rural children, and girls. High scholastic achievement is associated with lower workloads for girls, but not boys. This pattern is interpreted as daughter-biased investment in the context of urbanization.

Review of Nancy Howell’s Life Histories of the Dobe !Kung: Food, Fatness, and Well-Being over the Life-Span (Berkeley: University of California Press, 2010)

Abstract: This well-written book describes reanalyses of existing anthropometric and behavioral data on the !Kung of northern Botswana, the same data that previously underpinned Howell’s (1979) classic and much admired volume, The Demography of the Dobe !Kung (New York: Academic Press). Since that book was published, increasing interest has been directed to analyzing the life history profiles of various foraging populations. Howell has used this publication both to contribute to this active area of research and to make her raw data more widely available to potential users, especially to students. On both counts, this very generous book is an elegant guide that shows how seemingly simple anthropometric and dietary data can be used to tease out answers to fundamental questions in human ecology and life history. Howell’s particular interest is in understanding how the nutritional status of the Dobe !Kung population correlates with energy capture from the environment and, in particular, who funds the expensive growth costs of children who, until adulthood, invariably consume more calories than they produce. To address these issues, she examines data on weight, height, and skinfold thicknesses to assess nutritional status, along with predictions of energy requirements based on body weight and physical activity data, and relates these to data on family size and structure. Weight is, by convention, adjusted for height to yield a body mass index (BMI), or relative weight. A key outcome in her analyses is therefore “BMIdifference,” the discrepancy between a typical BMI for someone of a given age and sex and the observed value. This difference is generally interpreted as an index of “relative fatness.” Hum Nat (2011) 22:370–375 DOI 10.1007/s12110-011-9121-9