Suresh, S.; Linksvayer, T. A.

As a corollary to inclusive fitness theory, W.D. Hamilton\'s famous haplodiploid hypothesis proposed that eusociality evolves more readily in haplodiploids because of an inflated genetic relatedness between sisters. For the past sixty years, theoreticians have developed an array of models that further clarify how eusociality might evolve more readily in haplodiploids. Despite this sustained theoretical interest, the predicted evolutionary association between haplodiploidy and eusociality was only recently empirically tested when a family-level analysis in insects found mixed support. Here, we use a large species-level insect phylogeny with all available sociality and ploidy trait data to test whether there is an evolutionary association between haplodiploidy and eusociality. We show that the transition rate from solitary to eusocial life was 15-100 times higher in haplodiploid than diploid lineages, depending on the definitions of eusociality and haplodiploidy. Our results strongly support the prediction of the haplodiploid hypothesis and related models that the evolutionary transition from solitary to eusocial life is facilitated by haplodiploidy.