Willingness to Invest in Children: Psychological Kinship Estimates and Emotional Closeness.

In general, adults invest more in related children compared to unrelated children. To test whether this pattern reflects variations in psychological kinship estimates (i.e., putative relatedness weighted by certainty in relatedness), willingness to invest in children belonging to different categories (direct offspring, nieces/nephews, stepchildren, and friends' children) was measured in a population-based sample of 1,012 adults. Respondents reported more willingness to invest in their own biological children, than in other related children (nieces and nephews), or in stepchildren and friends' children. Compared to putative relatedness, respondents' psychological kinship estimates better predicted the willingness to invest. This association was partially mediated by emotional closeness. Additionally, the age of a child and the number of children in the care of the respondent were negatively associated with willingness to invest. The association between psychological kinship estimates and willingness to invest supports evolutionary predictions. Investment in stepchildren was, however, higher than expected.