The importance of kin relationships was investigated across adulthood with 5 samples (total N = 1,365). Within the personal networks, the genetic relatedness with relationship partners predicted subjective closeness (mean r = .50) and social support (mean r = .13). Effects were robust in 2 samples when controlling for residential proximity and contact frequency. These intraindividual correlations showed considerable variability and were interpreted as individual expressions of nepotism. The heritability of individual nepotism was zero. Variability of nepotism was unrelated to personality traits, but substantially related to sex, and parental and partner status. The authors discuss subjective closeness as 1 proximate cue to kinship, and suggest nepotistic adaptations as powerful mechanisms in social relationships.