Ecological and genetic distribution of eusociality: the case for kin selection

The evolutionary origin of eusociality has been the subject of much recent debate. In particular, the role of haplodiploidy has been questioned. With the aim of contributing to our understanding of this process, I propose the classification of eusociality into 2 kinds: female-only and male–female eusocial societies. The former occurs in haplodiploid animals, whereas the latter evolved in animals that live inside their food. In female-only eusociality, females are highly related because of haplodiploidy, whereas in male–female eusociality, living inside food promotes inbreeding among both male and female colony members, leading to both sexes being highly related. By reviewing the occurrence of these 2 kinds of extremely altruistic social systems, I argue that kin selection is crucial in both cases, giving support to the hypothesis that haplodiploidy was essential for the evolution of eusociality in animals possessing this trait.