I enjoyed reading this is a fascinating piece of work, showing a remarkable and little known aspect of chimpanzee behaviour. Adoption is something that seems to happen repeatedly amongst Tai chimpanzees. However, I think the authors are too hasty dismissing the role of kin selection in shaping this behaviour. I think the problem stems in the difficulty of estimating the relatedness of wild chimpanzees. If individuals are not parent/offspring or siblings they are considered ‘unrelated’ – although this I based on previous studies on this population, as no reference is given to the relation aspect on Table. But what about aunts and uncles? Assuming that full siblings are rare (uncle, aunt)/(nephew, niece) will have a relatedness of 0.125, and therefore, a lot of power is needed by markers to resolve this 9 microsatellite loci is likely not to be enough to ascertain relatedness beyond filial sibling relatedness). However, the long-term studies of chimp communities have revealed the close affiliations of mother and offspring, which appear to extend to adulthood. The life-long relationships of families through the maternal line indicate that opportunities will be present to individuals (males and females) to be aware of their relationship to their sisters’ offspring. I think the strong family ties of chimpanzees make it likely that at least some of the ‘friends’ of the mother in Table 2 are actually maternal aunts/uncles. A testable hypothesis would be that maternal uncles should be more likely to adopt their nieces/nephews than paternal uncles.