Lineal kinship organization in cross-specific perspective.

I draw on insights from anthropology to outline a framework for the study of kinship systems that applies across animal species with biparental sexual reproduction. In particular, I define lineal kinship organization as a social system that emphasizes interactions among lineally related kin-that is, individuals related through females only, if the emphasis is towards matrilineal kin, and individuals related through males only, if the emphasis is towards patrilineal kin. In a given population, the emphasis may be expressed in one or more social domains, corresponding to pathways for the transmission of different resources across generations (e.g. the allocation of food, the transfer of access to the natal territory or household). A lineal bias in any domain can be viewed as a bias in investment towards a particular set of kin-specifically, towards the offspring of daughters if the bias is matrilineal, and towards the offspring of sons if the bias is patrilineal. Effectively, investment is restricted to the offspring of the females in the population in one case, and to the offspring of the males in the other. This is distinct from a bias in investment towards daughters and towards sons, respectively. Overall, I propose a shift in focus-from viewing matrilineal and patrilineal kinship as unitary phenomena, to consideration of the different aspects of the social system featuring a bias towards lineally related kin. This article is part of the theme issue 'The evolution of female-biased kinship in humans and other mammals'.