Kinship ties across the lifespan in human communities

Abstract

A hypothesis for the evolution of long post-reproductive lifespans in the human lineage involves asymmetries in relatedness between young immigrant females and the older females in their new groups. In these circumstances, inter-generational reproductive conflicts between younger and older females are predicted to resolve in favour of the younger females, who realize fewer inclusive fitness benefits from ceding reproduction to others. This conceptual model anticipates that immigrants to a community initially have few kin ties to others in the group, gradually showing greater relatedness to group members as they have descendants who remain with them in the group. We examine this prediction in a cross-cultural sample of communities, which vary in their sex-biased dispersal patterns and other aspects of social organization. Drawing on genealogical and demographic data, the analysis provides general but not comprehensive support for the prediction that average relatedness of immigrants to other group members increases as they age. In rare cases, natal members of the community also exhibit age-related increases in relatedness. We also find large variation in the proportion of female group members who are immigrants, beyond simple traditional considerations of patrilocality or matrilocality, which raises questions about the circumstances under which this hypothesis of female competition are met. We consider possible explanations for these heterogenous results, and we address methodological considerations that merit increased attention for research on kinship and reproductive conflict in human societies. This article is part of the theme issue ‘The evolution of female-biased kinship in humans and other mammals’.

Gender Differences in Social Networks Based on Prevailing Kinship Norms in the Mosuo of China

“…Shih, 1993), as may the relative ease with which individuals travel from house-to-house in this relatively traversable terrain (Mathieu, 2003;Mattison et al, 2021). This result, even if tentative, reinforces the importance of differences in the social and demographic constraints imposed by kinship systems in structuring access to social support and the costs and benefits to men and women of gender-specific strategies (Koster Jeremy et al, 2019;Low, 2005;Power & Ready, 2019;Starkweather et al, 2020), with important implications for understanding strategies across diverse contemporary settings (David-Barrett, 2019;Mattison & Sear, 2016).…”

Social support, nutrition and health among women in rural Bangladesh: complex tradeoffs in allocare, kin proximity and support network size

“…Families live in close proximity to each other in residential complexes called baris which often include families related patrilocally but may also include unrelated individuals. Patrilocal postmarital residence norms mean that young women are much more likely to live close to their in-laws than their natal kin, but as they age and their children mature, they become increasingly socially integrated with, as well as related to, the other members of their residential area [50]. Related households are often economically inter-reliant; loans of royalsocietypublishing.org/journal/rstb Phil.…”

The evolution of female-biased kinship in humans and other mammals

“…In particular, an influential model [42] proposes that relatedness to group increases with age, impacting natal versus immigrant community members differently, and affecting willingness to cede reproduction to subsequent generations. In this issue, Koster et al [10] measure the relationship between relatedness to one's community as this changes over the lifespan, in numerous human societies adhering to different norms of locality. Once again, community norms were imperfect predictors of kinship structure, suggesting that facultative dispersal patterns should be considered in models of sex-biased competition for resources among kin.…”

“…In addressing these issues, we extend previous perspectives that have often focused more narrowly on matrilineal kinship. To this end, we include empirical analyses informed by theoretical models derived from the study of kinship across species [10,11], including articles describing taxa and circumstances under which FBK emerges as most prominent [9,12,13]. As highlighted below, these articles describe hypotheses that are novel to, yet could be fruitfully tested in, humans.…”