“Consistent with inclusive fitness theory, evolutionary biologists predict that individuals care more for their biological than their social children and hence that biological children assess the relationships to their parents better than stepchildren. To test this assumption, we use data from the U.S. National Longitudinal Study of Adolescent Health (Add Health). Unlike many other studies that have been conducted so far, this survey allows us to analyze the consequences of the dynamic between social and biological parent-child relationships within the same families. We use comparisons of sibling pairs and fixed-effects regression to achieve the within-family comparison. Both the descriptive and multivariate regression results confirm that – even after controlling for other relevant influences – biological parenthood matters with regard to children’s relationship assessments (perceived parental care and closeness of the parent-child relationship) and in both the relationships to resident fathers and mothers. In the discussion, we comment on the possible integration of the evolutionary and sociological perspectives and close with some recommendations for future data collection that could allow researchers to analyze the relative influence of biological and social influences on parent-child relationships on a more fine-grained level….
“Starting point of this paper was the assumption that from an evolutionary perspective, parental care should differ between biological and social children in a way that disadvantages the latter, and that this difference should be mostly visible in families in which biological and social parent-child relations coexist…. The conclusion of the analysis is that biological parenthood matters: In all respects stepchildren do provide lower assessments of the relationships to their parents than biological children do.”
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