Fitness consequences of spousal relatedness in 46 small-scale societies

Drew H. Bailey, Kim Hill, Robert S. Walker

Research output: Contribution to journalArticle

9 Scopus citations

Abstract

Social norms that regulate reproductive andmarital decisions generate impressive cross-cultural variation in the prevalence of kinmarriages. In some societies, marriages among kin are the norm and this inbreeding creates intensive kinship networks concentrated within communities. In others, especially forager societies, most marriages are between more genealogically and geographically distant individuals, which generates a larger number of kin and affines of lesser relatedness in more extensive kinship networks spread out over multiple communities. Here,we investigate the fitness consequence of kin marriages across a sample of 46 small-scale societies (12 439 marriages). Results show that some non-forager societies (including horticulturalists, agriculturalists and pastoralists), but not foragers, have intensive kinship societies where fitness outcomes (measured as the number of surviving children in genealogies) peak at commonly high levels of spousal relatedness. By contrast, the extensive kinship systems of foragers have worse fitness outcomes at high levels of spousal relatedness. Overall, societies with greater levels of inbreeding showed a more positive relationship between fitness and spousal relatedness.

Original languageEnglish (US)
Article number20140160
JournalBiology letters
Volume10
Issue number5
DOIs
StatePublished - May 2014

Keywords

  • Agriculture
  • Fertility
  • Foragers
  • Human kinship
  • Marriage patterns
  • Subsistence

ASJC Scopus subject areas

  • Agricultural and Biological Sciences (miscellaneous)
  • Agricultural and Biological Sciences(all)

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