Russell D. Greaves

Early reproductive maturity among Pumé foragers: Implications of a pooled energy model to fast life histories.

Life history theory places central importance on relationships between ontogeny, reproduction, and mortality. Fast human life histories have been theoretically and empirically associated with high mortality regimes. This relationship, however, poses an unanswered question about energy allocation. In epidemiologically stressful environments, a greater proportion of energy is allocated to immune function. If growth and maintenance are competing energetic expenditures, less energy should be available for growth, and the mechanism to sustain rapid maturation remains unclear. The human pattern of extended juvenile provisioning and resource sharing may provide an important source of variation in energy availability not predicted by tradeoff models that assume independence at weaning. We consider a group of South American foragers to evaluate the effects that pooled energy budgets may have on early reproduction. Despite growing up in an environment with distinct seasonal under‐nutrition, harsh epidemiological conditions, and no health care, Pumé girls mature quickly and initiate childbearing in their midteens. Pooled energy budgets compensate for the low productivity of girls not only through direct food transfers but importantly by reducing energy they would otherwise expend in foraging activities to meet metabolic requirements. We suggest that pooled energy budgets affect energy availability at both extrinsic and intrinsic levels. Because energy budgets are pooled, Pumé girls and young women are buffered from environmental downturns and can maximize energy allocated to growth completion and initiate reproduction earlier than a traditional bound‐energy model would predict. Am. J. Hum. Biol., 2009.

Postmarital Residence and Bilateral Kin Associations among Hunter-Gatherers

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 Pumé 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 Pumé have been characterized as matrilocal. Analysis of Pumé 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.

Synchrony between growth and reproductive patterns in human females: Early investment in growth among Pumé foragers

Life history is an important framework for understanding many aspects of ontogeny and reproduction relative to fitness outcomes. Because growth is a key influence on the timing of reproductive maturity and age at first birth is a critical demographic variable predicting lifetime fertility, it raises questions about the synchrony of growth and reproductive strategies. Among the Pumé, a group of South American foragers, young women give birth to their first child on average at age 15.5. Previous research showed that this early age at first birth maximizes surviving fertility under conditions of high infant mortality. In this study we evaluate Pumé growth data to test the expectation that if early reproduction is advantageous, then girls should have a developmental trajectory that best prepares them for young childbearing. Analyses show that comparatively Pumé girls invest in skeletal growth early, enter puberty having achieved a greater proportion of adult body size and grow at low velocities during adolescence. For early reproducers growing up in a food-limited environment, a precocious investment in growth is advantageous because juveniles have no chance of pregnancy and it occurs before the onset of the competing metabolic demands of final reproductive maturation and childbearing. Documenting growth patterns under preindustrial energetic and demographic conditions expands the range of developmental variation not otherwise captured by normative growth standards and contributes to research on human phenotypic plasticity in diverse environments.

Living with Kin in Lowland Horticultural Societies

Postmarital residence patterns in traditional human societies figure prominently in models of hominid social evolution with arguments for patrilocal human bands similar in structure to female-dispersal systems in other African apes. However, considerable flexibility in hunter-gatherer cultures has led to their characterization as primarily multilocal. Horticulturalists are associated with larger, more sedentary social groups with more political inequality and intergroup conflict and may therefore provide additional insights into evolved human social structures. We analyze coresidence patterns of primary kin for 34 New World horticultural societies (6,833 adults living in 243 residential groupings) to show more uxorilocality (women live with more kin) than found for hunter-gatherers. Our findings further point to the uniqueness of human social structures and to considerable variation that is not fully described by traditional postmarital residence typologies. Sex biases in coresident kin can vary according to the scale of analysis (household vs. house cluster vs. village) and change across the life span, with women often living with more kin later in life. Headmen in large villages live with more close kin, primarily siblings, than do nonheadmen. Importantly, human marriage exchange and residence patterns create meta-group social structures, with alliances extending across multiple villages often united in competition against other large alliances at scales unparalleled by other species.

Juvenile Subsistence Effort, Activity Levels, and Growth Patterns

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 Pumé, 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 Pumé 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.

Hunting and Multifunctional Use of Bows and Arrows

Stone tools and the debris from their manufacture are the most common remains from archaeological sites all over the world. Unraveling how prehistoric people made and used their technology is a major challenge of archaeological interpretation. Many archaeologists have sought to understand the organization of technology through an emphasis on the internal production mechanics of stone tools. This approach has been used to study behavioral tactics through examination of the inferred design of lithic reduction strategies. Such studies implicate aspects of behavior that can be monitored through differential raw material use (Ahler 1977; Bamforth 1986; Goodyear 1979; Jeske 1989; Kuhn 1991; Wiant and Hassen 1985; Winters 1984), production trajectories (Bradley 1975; Collins 1975; Dibble 1988; Muto 1971), tool design, and use life (Bleed 1986; Gurfinkel and Franklin 1988; Hayden 1989; Keeley 1980; Kelly 1988; Kuhn 1994; Shott 1986, 1989a, 1989b; Vaughan 1985).

Seasonality and Sex Differences in Travel Distance and Resource Transport in Venezuelan Foragers

The anthropological literature generally describes forager women as less mobile than men because of their child-care responsibilities and the energetic costs of reproduction. Examination of resource transport among the savanna Pumé of southwestern Venezuela reveals, in contrast, that for certain food resources travel distances and resource weights relative to body weights are greater for women than for men. Male foraging is often associated with greater travel distances, but men frequently walk unencumbered because hunting trips may exhibit low or zero food returns and hunters usually carry only a minimum tool kit. Women, who target highly predictable foods that can be collected in large quantities, frequently carry firewood, tools, and large baskets of food for extended distances during gathering. It appears that the consistent and large returns of female foraging underwrite the large energetic effort of mens hunting.

Age, Sex, and Resource Transport in Venezuelan Foragers

Enhancing our understanding of the skeletal biology of modern hunter-gatherers and developing more sophisticated models of fossil and prehistoric hominin locomotor behavior and subsistence activities requires information on male and female forager mobility patterns. Unlike other primates, modern human foragers expend considerable energy in activities involving the transport of resources across the landscape. Although male foragers are often associated with high mobility in comparison to their female counterparts, female foragers are seen to engage in subsistence tasks incorporating a high frequency of burden carrying. This paper examines the influence of age and sex on mobility and resource transport in a group of Pume foragers located in the savanna-wetlands of southwestern Venezuela.

Mobility and Navigation among the Yucatec Maya Sex Differences Reflect Parental Investment, Not Mating Competition

Sex differences in range size and navigation are widely reported, with males traveling farther than females, being less spatially anxious, and in many studies navigating more effectively. One explanation holds that these differences are the result of sexual selection, with larger ranges conferring mating benefits on males, while another explanation focuses on greater parenting costs that large ranges impose on reproductive-aged females. We evaluated these arguments with data from a community of highly monogamous Maya farmers. Maya men and women do not differ in distance traveled over the region during the mate-seeking years, suggesting that mating competition does not affect range size in this monogamous population. However, men’s regional and daily travel increases after marriage, apparently in pursuit of resources that benefit families, whereas women reduce their daily travel after marriage. This suggests that parental effort is more important than mating effort in this population. Despite the relatively modest overall sex difference in mobility, Maya men were less spatially anxious than women, thought themselves to be better navigators, and pointed more accurately to distant locations. A structural equation model showed that the sex by marital status interaction had a direct effect on mobility, with a weaker indirect effect of sex on mobility mediated by navigational ability.

Infant growth and the thymus: Data from two South American native societies

The thymus plays an important role in the development of the immune system, yet little is known about the patterns and sources of variation in postnatal thymic development. The aim of this study is to contribute cross‐cultural data on thymus size in infants from two South American native populations, the Tsimane of Bolivia and the Pumé of Venezuela. Thymic ultrasonography was performed and standard anthropometric measures collected from 86 Tsimane and Pumé infants. Patterns of infant growth and thymus size were compared between the two populations and the relationship between nutritional status and thymus size was assessed. Despite nearly identical anthropometric trajectories, Tsimane infants had larger thymuses than Pumé infants at all ages. Population, infant age, and infant mid‐upper arm circumference were significant predictors of thymus area in the Tsimane and Pumé infants. This finding reveals a cross‐cultural difference in thymus size that is not driven by nutritional status. We suggest that future studies focus on isolating prenatal and postnatal environmental factors underlying cross‐cultural variation in thymic development. Am. J. Hum. Biol., 2012.