In most social species, position in the male social hierarchy and reproductive success are positively correlated; in humans, however, this relationship is less clear, with studies of traditional societies yielding mixed results. In the most economically advanced human populations, the adaptiveness of status vanishes altogether; social status and fertility are uncorrelated. These findings have been interpreted to suggest that evolutionary principles may not be appropriate for the explanation of human behavior, especially in modern environments. The present study tests the adaptiveness (...) of social status with actual mating and reproductive data in a representative sample of males from an industrial society. Reproductive success, even when assessed by a more reliable measure ofactualmale fertility than the one commonly used, fails to correlate with social status. In striking contrast, however, status is found to be highly correlated withpotentialfertility, as estimated from copulation frequency. Status thus accounts for as much as 62% of the variance in thisproximatecomponent of fitness. This pattern is remarkably similar to what is found in many traditional societies and would result in a substantial positive relationship between cultural and reproductive success in industrial populations were it not for the novel conditions imposed by contraception and monogamy. Various underlying mechanisms are suggested for these findings, illustrating the value of current behavioral and reproductive data in the study of adaptation. It is concluded that evolutionary explanations of human behavior remain entirely relevant in modern societies. (shrink)

Female-biased parental investment is unusual but not unknown in human societies. Relevant explanatory models include Fisher’s principle, the Trivers-Willard model, local mate and resource competition and enhancement, and economic rational actor models. Possible evidence of female-biased parental investment includes sex ratios, mortality rates, parents’ stated preferences for offspring of one sex, and direct and indirect measurements of actual parental behavior. Possible examples of female-biased parental investment include the Mukogodo of Kenya, the Ifalukese of Micronesia, the Cheyenne of North America, the (...) Herero of southern Africa, the Kanjar of south Asia, the Mundugumor of New Guinea, contemporary North America, and historical Germany, Portugal, and the United States. (shrink)

A historical survey of the inheritance practices of farming families in North America and elsewhere indicates that resource allocations among children differed through time and space with regard to sex bias and equality. Tensions between provisioning all children and maintaining a productive economic entity (the farm) were resolved in various ways, depending on population pressures, the family’s relative resource level, and the number and sex of children.Against a backdrop of generalized son preference, parents responded to ecological circumstances by investing in (...) offspring differentially within and between the sexes. Vesting the preponderance of family resources in one heir increased the likelihood of at least one line surviving across several generations, whereas varying degrees of parental investment in emigrating sons or out-marrying daughters might yield boom or bust harvests of grandchildren according to circumstances in more remote locales. Primogeniture (eldest son as primary heir) allowed early identification of heirs and appropriate socialization, as well as more time for parents to contribute to the heir’s reproductive success. Son bias and unigeniture decreased as numbers of children per family declined, as land became less critical to economic success, and as legal changes improved the resource-holding potential of females. We suggest that changing ecological conditions affected parental decisions regarding resource allocation among children at least as much as did changing ideologies of parent-child relations. (shrink)

The well-established finding that siblings growing up in the same family turn out to be very different from one another has puzzled psychologists and behavior geneticists alike. In this theoretical note we describe the possible ontogeny and phylogeny of a sibling differentiation mechanism. We suggest that sibling competition for parental investment results in sibling differentiation on a number of characteristics, producing different developmental trajectories within families. Variations in developmental trajectories within families may have had fitness advantages in ancestral environments because(a) (...) sibling competition for extrafamilial resources would be reduced and(b) these variations would be suited to environments containing a variety of niches or to changing environments. Predictions derived from this model and an example of an application to attachment theory are presented. (shrink)

Why do men and women compete? And what makes them compete more or less? An answer to the first question follows directly from Darwin. If Homo sapiens, like other species, is a product of natural selection, then we should have evolved to compete in order to reproduce. An answer to the second question follows from more recent versions of Darwinism. People, like other organisms, are likely to compete socially - to form dominance hierarchies - to the extent that it is (...) costly for subordinates to flee ecologically. This paper first reviews evidence that winners at political competition have consistently won at reproductive competition. Next, it documents the slow shift toward declining political competition - toward democracy, and toward declining reproductive competition - toward monogamy, in the course of Western history. Last, it offers a model of what might account for that change. (shrink)