Diluted Competition? Conflicts between Full- and Half-Siblings in Two Adult Generations

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.

Migration patterns of parents, children and siblings: Evidence for patrilocality in contemporary Finland

“…However, these differences almost disappeared with age. This is an interesting finding, indicating that despite the many documented differences between full and half siblings (e.g., Salmon & Hehman, 2015;Tanskanen et al, 2016), geographical differences between full and half siblings are negligible in contemporary Finland, at least on a regional scale. Future research should preferably investigate the topic with more detailed measures of geographical distance.…”

“…This difference is likely to affect family relationship dynamics (Rotkirch, ). Different degrees of relatedness may influence geographical proximity, conflict, and support between siblings (e.g., Hughes, ; Tanskanen, Danielsbacka, Jokela, David‐Barrett, & Rotkirch, ). However, most previous studies, including all sibling studies mentioned above, have investigated only relations between full siblings.…”

Communication with Family and Friends across the Life Course

“…Siblings, although very important for life course competition and support [31, 32], have to be excluded in this study, for reasons explained in the data section. Friendship is defined as a tie between two individuals who are not relatives, of the same sex, and not romantically involved.…”

The “Kinship Penalty”: Parenthood and In-Law Conflict in Contemporary Finland

“…One reason for conflicts within close family is that family members compete over resources, and the severity of kin competition may reduce or even overrun the tendencies to altruistic helping among kin (Griffin and West, 2002;Mace, 2013;Tanskanen et al, 2016aTanskanen et al, , 2016b. Inclusive fitness theory has usually been interpreted as predicting less competition and fewer conflicts with close genetic kin compared to more distant kin and non-kin (e.g., Salmon and Hehman, 2014).…”

“…Inclusive fitness theory has usually been interpreted as predicting less competition and fewer conflicts with close genetic kin compared to more distant kin and non-kin (e.g., Salmon and Hehman, 2014). This assumption has been shown to be problematic when kin competition is involved, as between siblings (e.g., Salmon and Hehman, 2015;Tanskanen et al, 2016b). Additionally, the presence of a young and dependent generation in the kin network could increase conflict occurrence between different generations.…”