The evolution of same-sex sexual behaviour in mammals

Same-sex sexual behaviour has attracted the attention of many scientists across disciplines because, despite not contributing directly to reproduction, it is widespread and presents an evolutionary puzzle. Using phylogenetic analyses, this study explores the evolution of same-sex sexual behaviour in mammals. Available data indicate the behaviour is non-randomly distributed across lineages and is particularly prevalent in some clades, especially primates. Ancestral state reconstructions suggest multiple independent origins, with a generally recent appearance in most mammalian lineages. Phylogenetically informed analyses testing associations with species characteristics indicate that same-sex sexual behaviour may have adaptive roles in social relationships and mitigating conflict.