Abstract

Sibling relations are typically close but ambivalent, including both altruism and competition. Full siblings are often assumed to exhibit more altruism and less competition than half-siblings. However, previous empirical findings indicate that this assumption may not hold for sibling conflicts in contemporary humans. We study self-reported occurrence of sibling conflicts among adults in two generations with nationally representative data from the Generational Transmissions in Finland surveys in 2012. Respondents represent an older generation (born between 1945 and 1950, n = 2,015) and their adult children (born between 1962 and 1993, n = 1,565). Based on kin selection and parent-offspring conflict theory we expect reports of any conflict to be more likely between full siblings than half siblings, between maternal half siblings than paternal half-siblings, and among the younger generation compared to the older generation. Results mostly support our hypotheses. Full siblings were more likely to report conflicts than were maternal and paternal half siblings in the younger generation. In the older generation, full siblings were more likely to report conflicts with paternal but not maternal half siblings. The younger generation was also more conflict-prone than the older. Results held when controlling for contact frequency, emotional closeness, unequal parental treatment, and several socioeconomic variables, as well as for within-family effects. Thus, although full siblings are typically closer and have more contact in adulthood than half siblings do, they also appear to have more conflicts. We suggest that this can be explained by diluted resource competition over parental investment between half siblings in societies with serial monogamy.

Highlights

  • Sibling competition has been documented across species, and may manifest itself in many forms ranging from minor quarrels to aggression and siblicide (Mock and Parker, 1997; Michalski and Euler, 2008)

  • Sibling relations are usually life-long, important and complex, yet relatively few studies have investigated the conflictual side of sibling relations in adulthood using large data

  • We studied how the likelihood of sibling conflict is associated with genetic relatedness in two adult family generations from contemporary Finland

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Summary

INTRODUCTION

Sibling competition has been documented across species, and may manifest itself in many forms ranging from minor quarrels to aggression and siblicide (Mock and Parker, 1997; Michalski and Euler, 2008). Such blended families are increasingly common in contemporary Europe, where children usually reside with their mothers if parents have separated, but their biological fathers continue to keep in contact with and provide support for them (Amato, 2010) This creates a crucial difference between full and half-siblings in terms of the kin network they can expect most investment from. The younger adults were closer in time to their childhood, when they probably had more intense competition over parental resources and more conflicts with their siblings They were more likely to have at least one parent alive, compared to the older generation whose parents have usually already both died (Statistics Finland, 2012). Regression coefficients were expressed as odds ratios (ORs) for which an OR above 1 indicates a positive association between the independent variable and the outcome, while ORs under 1 indicate a negative association

RESULTS
A Comparison between Generations
DISCUSSION
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