Data from the Kipsigis of Kenya are used to test two models for how parents invest in offspring, the Trivers-Willard and local resource competition/enhancement hypotheses. Investment is measured as age-specific survival, educational success, marital arrangements, and some components of property inheritance, permitting an evaluation of how biases persist or alter over the period of dependence. Changes through time in such biases are also examined. Despite stronger effects of wealth on the reproductive success of men than women, the survival of sons (...) and daughters is not related to parental wealth. However, a Trivers-Willard effect characterizes educational investment: poor families show a greater concern for daughters’ (vis-à-vis sons’) schooling than do rich families, a trend that has increased over time. In regard to models of local resource competition and enhancement, men’s reproductive success decreases with number of brothers and increases with number of sisters; this pattern of competition with same-sex sibs and cooperation with opposite-sex sibs is not found among women. As predicted from these observations, parents show reduced investment in sons with a large number of brothers, and increased investment in sons with a large number of sisters. By contrast, investment in daughters is entirely unaffected by number of sisters and is influenced only in subtle ways by number of brothers. Levels of investment in relation to sibship size (irrespective of siblings’ sex) are highest for younger children of large sib sets.Discussion of the results in relation to those from other studies leads to three conclusions. First, predictive models for how investment biases vary across societies must consider a broad range of socioecological factors constraining parental options and payoffs. Second, the timing of investment biases within societies will be affected by the value of children and the costs of parental investment. Third, measures of investment appropriate for between-sex and between-class comparisons need careful attention. Each of these issues is brought to bear on the question of why, in contrast to so many other parts of the world, sex preferences are so muted in Africa. (shrink)

Both behavioral ecological and social anthropological analyses of polygynous marriage tend to emphasize the importance of competition among men in acquisition of mates, whereas the strategic options to women both prior to and after the establishment of a marriage have been neglected. Focusing on African marriage systems that are in some senses analogous to resource-defense polygyny, I first review the evidence of reproductive costs of polygyny to women. Then I discuss why the conflict of interests between men and women over (...) mate number is often likely to be settled in favor of men. Using East African ethnographic data I examine the strategic responses of women and their families to polygynous marriage, focusing on four topics: mate choice (Kipsigis), attitudes toward incoming wives (Kipsigis), labor allocation and cooperation (comparative data, Kipsigis), and use of parental wealth (Datoga). The results of these quantitative analyses suggest that through a combination of judicious marriage choice and strategic responses within marriage, polygyny need not be costly to women in resource-defense polygynous systems. The conclusion is that a hierarchy of questions need to be addressed in the analysis of any polygynous marriage system. (shrink)

What are the driving forces of cultural macroevolution, the evolution of cultural traits that characterize societies or populations? This question has engaged anthropologists for more than a century, with little consensus regarding the answer. We develop and fit autologistic models, built upon both spatial and linguistic neighbor graphs, for 44 cultural traits of 172 societies in the Western North American Indian (WNAI) database. For each trait, we compare models including or excluding one or both neighbor graphs, and for the majority (...) of traits we find strong evidence in favor of a model which uses both spatial and linguistic neighbors to predict a trait’s distribution. Our results run counter to the assertion that cultural trait distributions can be explained largely by the transmission of traits from parent to daughter populations and are thus best analyzed with phylogenies. In contrast, we show that vertical and horizontal transmission pathways can be incorporated in a single model, that both transmission modes may indeed operate on the same trait, and that for most traits in the WNAI database, accounting for only one mode of transmission would result in a loss of information. (shrink)

Tracing the historical roots of modern conservation thought & practice, this book explores current perspectives from evolutionary & community ecology, conservation biology, anthropology, political ecology, economics, and policy.