Patterns of human kinship commonly involve preferential treatment of relatives based on lineal descent (lineages) rather than degree of genetic relatedness (kindreds), presenting a challenge for inclusive fitness theory. Here, we examine effects of lineage and kindred characteristics on reproductive success (RS) and number of grandchildren for 130 men and 124 women in a horticultural community on Dominica. Kindreds had little effect on fitness independently of lineage characteristics. Fitness increased with the number of lineal relatives residing in the community but (...) decreased beyond an apparently optimal lineage size, suggesting resource enhancement and competition among kin. Female-biased patrilineage sex ratio was positively associated with men’s fitness, while male-biased matrilineage sex ratio was positively associated with women’s fitness. Number of brothers in the community was negatively associated with men’s, but not women’s, fitness. Parents and number of sisters had no effect on either male or female reproduction; however, women with younger sisters had higher RS, suggesting benefits of kin support for childcare. In sum, imposed norms for lineage social organization may enhance lineal ancestors’ inclusive fitness at a cost to individual inclusive fitness. (shrink)

The purpose of this article is to develop a model of life history theory that incorporates environmental influences, contextual influences, and heritable variation. I argue that physically or psychologically stressful environments delay maturation and the onset of reproductive competence. The social context is also important, and here I concentrate on the opportunity for upward social mobility as a contextual influence that results in delaying reproduction and lowering fertility in the interest of increasing investment in children. I also review evidence that (...) variation in life history strategies is influenced by genetic variation as well. Finally, I show that cultural shifts in the social control of sexual behavior have had differential effects on individuals predisposed to high- versus low-investment reproductive strategies. (shrink)