American journal of human biology : the official journal of the Human Biology Council
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Recent research suggests that evolutionary selection pressures have shaped mental mechanisms to be able to assess one's own and other's physical strength, fighting ability, and aggressiveness. According to the recalibrational theory, anger may be linked to fighting ability and serve as a bargaining mechanism to improve welfare obtained in social conflict. We hypothesized that late adolescent men (but not mid-adolescent men or women) use this mechanism, as it would be particularly adaptive for them to avoid potential costs from direct conflict in male competition. ⋯ With reference to the recalibrational theory of anger, our results suggest that the sex- and age-dependent associations between fighting ability and physical and nonphysical aggression indicate divergent adaptive skills between sexes, which are driven by intrasexual competition.
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The association between a woman's age at menarche and the birth weight of her children is highly variable across human populations. Life history theory proposes that a woman's early environment may moderate this association and thus account for some of the variation between populations. According to one life history theory model, for individuals who develop in a childhood environment of high local mortality rates (experienced subjectively as psychosocial stress), it can be adaptive to mature earlier, have more offspring during their reproductive lifetime, and reduce investment in each offspring. ⋯ We found that earlier menarche in those women who experienced stressful life events before 15 years of age was associated with a lower birth weight and proportionate birth weight. Conversely, in those who reported no childhood stressors, earlier menarche was associated with increased birth weight and proportionate birth weight. Our data suggest that the moderating influence of the childhood psychosocial environment on the association between age at menarche and parental investment throughout gestation operates in a dose-dependent manner.
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Senescence arises from age-specific deterioration of the soma as a consequence of optimization of life history, and such effects of senescence should appear when comparing species that differ in intensity of sexual selection, as well as when comparing, within a species, the two sexes that often differ in intensity of sexual selection. However, any extrinsic cause of mortality that reduces life expectancy will reduce the possibility of detecting sex-specific differences in senescence. We investigated geographical variation in human sex differences in longevity across 121 countries to test whether differences in sexual competition for limiting resources, reflecting intensity of sexual selection, affected sex differences in longevity. ⋯ In a separate analysis of sex differences in longevity among the states of the US, there was a strong effect of the Gini coefficient on sex difference in longevity, with the negative effect on male longevity being stronger than that on female longevity. In contrast, there was only a marginal effect of average household income. Thus, there was evidence of increased competition for resources contributing to increased sex differences in longevity within a single nation.
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We analyzed the nutritional status of urban and rural schoolchildren from Mendoza (Argentina), but avoided rural and urban categorization by generating subpopulations as a function of their socioenvironmental characteristics. We transformed weight and height data into z-scores using the CDC/NCHS growth charts; defined underweight, stunting, and wasting by z-scores of less than -2 SD; and calculated overweight and obesity, according to the cutoff proposed by the International Obesity Task Force. Socioenvironmental characteristics included housing, public services, parental resources, and farming practices; we processed these variables by categorical principal-component analysis. ⋯ Thus, the negative effects of environment on nutritional status in children are not restricted to poor periurban and rural areas, though these are indeed unfavorable environments for growth: some urban families provide children with sufficient quantity and diversity of foods to expose them to obesity. By contrast, the more affluent urban families would appear to have greater possibilities for allowing their children to adopt a healthy life-style. Although the causes of differences in nutritional status between middle- and high-income urban groups are not clear, these determinants probably involve economic as well as educational influences.
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1975 marked the end of a 20-year period of human biology research on physical environment. The focus then shifted from climatic adaptation to problems of nutrition, disease, and stress. However, many questions about human environmental patterns, especially in reference to their evolution, were abandoned rather than resolved. ⋯ Contrasts in environmental behaviors when comparing northern cultures such as Inuit, Athabaskan, and Norse are particularly instructive. Adaptations to life in the cold may ultimately reveal their secrets through biocultural research design modeling of environmental research. With both practical and theoretical gains still wide open, the field needs renewed attention from human biology.