Kin biased investment in wild chimpanzees

Kin selection theory predicts that recognition and preferences for kin can be highly beneficial. However, evidence of recognition of offspring by fathers in mammals has accumulated very slowly. Especially, in multi-male groups with a promiscuous mating system, like the chimpanzee, where offspring survival does not seem to depend on paternal care, paternal kin recognition has not yet been observed. In this study, we examined whether adult males of a wild chimpanzee community show recognition of their offspring (as determined genetically) and whether infants prefer to interact with kin rather than with unrelated peers. Our analysis utilises up to 14 years of observational data to investigate if adult males associate more frequently and behave less aggressively with females that carry their offspring. Furthermore, we use grooming and play behaviour to establish whether adult males and youngsters show preferences for kin versus non-kin. We found that, adult males did not associate preferentially with females with which they had offspring, but they were generally less aggressive towards any given female when she had a new born infant. Interestingly, however, fathers maintained these low rates of aggression long after the aggression rates of the non-sires had returned to their basal levels. Furthermore, fathers spent significantly more time playing with their own offspring. Thus, our data show for the first time that wild chimpanzee males can recognise their own offspring. Infants preferred to groom and tended to play more with their maternal siblings, but showed only a weak preference for playing with their paternal siblings when given the choice between similarly aged related and unrelated interaction partners. Despite the fact that paternal care does not play an obvious role in chimpanzee survival, kin recognition is observed in different aspects of the life of adult males and youngsters.