Postreproductive life predicted by primate patterns.

Regression analyses of primate life spans on recently revised female body and brain masses of Old World primates predict a human life span of between 72 years and 91 years-estimates that exceed the age of human menopause (and prior estimates) by well over 20 years. The life spans predicted from body and brain sizes in the early Homo suggest that postreproductive life spans predate Homo sapiens Among anthropoid primates, residual longevity after body and brain effects are controlled is greatest for Homo and for the New World monkeys of the genus Cebus. Body and brain masses predict a 25-year life span for Cebus, although recorded life spans exceed 50 years. Cebus are geographically widespread, have a female-bonded social organization convergent with Old World monkeys, and are primarily frugivorous, though the diet is heavily supplemented with vertebrate prey. Regressions of phylogenetically independent contrasts indicate that body mass and brain mass relationships to longevity remain significant when phylogeny is controlled and that brain mass is a more robust predictor than body mass. These data are new in terms of the completeness of species representation, more reliable body masses, presentation of various comparison group regressions, and control for phylogenetic independence.

American legacies and the variable life histories of women and men.

Sex differences in behavior are most interesting when they are the result of inherent differences in the operational rules motivating behavior and not merely a reflection of differing life history experiences. American men and women exhibit a few differences in testamentary patterns of property allocation that appear to be due to inherently different rules of allocation. Even when analyses control for resources and surviving kin configurations, women distribute their property among a greater number of individual beneficiaries than do men. The most striking differences in property allocation between men and women occur within the nuclear family and reflect differences in reproductive life span and the resulting reproductive conflicts between spouses that can endure beyond death.

Darwin and the puzzle of primogeniture : An essay on biases in parental investment after death.

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.