Encyclopedia of Evolutionary Psychological Science

Living Edition
| Editors: Todd K. Shackelford, Viviana A. Weekes-Shackelford

Same-Sex Friend

  • Minna LyonsEmail author
Living reference work entry
DOI: https://doi.org/10.1007/978-3-319-16999-6_1601-1



Same-sex friendships are lasting coalitions between individuals who are the same biological sex.


Friendships are intriguing cross-species phenomena that clearly contribute to both fitness and survival. Friendships involve coalitions based on altruistic interactions over a long period of time. Unlike opposite-sex friendships, same-sex friendships are less likely to include sexual motives. Although affiliative bonding is common in a large number of species, humans may be unique in the extent to which this happens among unrelated individuals. The theories that have been used to explain same-sex friendships are mainly reciprocal altruism and kin selection, which will be reviewed briefly below.

Kin Selection and Same-Sex Friendships

Research that investigates proximate determinants of friendships has found that friends are genetically similar (Christakis and Fowler 2014...

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Copyright information

© Springer International Publishing AG 2017

Authors and Affiliations

  1. 1.University of LiverpoolLiverpoolUK

Section editors and affiliations

  • Kevin Beaver
    • 1
  1. 1.Florida State UniversityTallahasseeUSA