Optimizing offspring: the quantity-quality tradeoff in agropastoral Kipsigis

The tradeoff between offspring quantity and offspring quality is at the heart of most evolutionary approaches to the fertility transition, as it is for demographers oriented towards economic explanations for this transition. To date, however, there have been few empirical tests of the key idea that humans trade offspring quantity for quality, and no strictly comparative work designed to identify the specific environmental conditions that favor such a tradeoff. This study suggests that in an East African community where the principal form of intergenerational inheritance is land, intermediate levels of offspring production are favored for women but not men. Women produce approximately the optimal number of surviving children, whereas men produce far fewer than the optimal number. The result highlights the significance of inheritable extrasomatic capital, in conjunction with evolved psychological mechanisms, in shaping fertility strategies that emphasize quality over quantity.