Genetic relatedness predicts contact frequencies with siblings, nieces and nephews: Results from the Generational Transmissions in Finland surveys

• Individuals have more contacts with full than with half siblings.
• Individuals have more contacts with nieces/nephews via full than via half siblings.
• Individuals have more contacts with nieces/nephews via sisters than via brothers.

Kin selection theory predicts that people should invest more in their full than their half siblings, and more in their nieces and nephews via full siblings than via half siblings. To study these predictions we use two nationally representative surveys that were collected as a part of the Generational Transmissions in Finland project. The subjects are representative of an older generation (born in 1945–1950) and a younger generation (born in 1962–1993). We found that both generations reported more contacts with full than with half siblings, and more with nieces and nephews via full than half siblings respectively. The results of the study are in line with the kin selection theory.