Social closeness of MZ and DZ twin parents towards nieces and nephews

Abstract

Twins' marriages to non‐twins yield genetically and socially informative kinships. Monozygotic (MZ) twins' genetic identity makes them ‘genetic parents’ of their nieces/nephews, and their nieces/nephews their ‘genetic children’. The present study is the first to apply twin‐family models to study social relatedness. Analyses of twin families (MZ: N = 248; DZ: N = 75) tested evolutionary‐based concepts concerning social closeness, perceived similarity and caretaking. Hypotheses based on Hamilton's inclusive fitness theory were supported: MZ twin aunts/uncles expressed greater social closeness towards their nieces/nephews than DZ twin aunts/uncles; and female twins from same‐sex pairs expressed greater closeness towards their nieces/nephews than male twins from same‐sex pairs. This study underlines benefits of associations between behavioural‐genetic and evolutionary psychological theories, methods and interpretations. Copyright © 2007 John Wiley & Sons, Ltd.