Sympatric speciation in animals: new wine in old bottles.

Recent research on natural host races and sympatric sister species, comparative phylogenetic analyses, laboratory experiments and theoretical models has greatly strengthened the case for sympatric speciation. Traits evolving in response to divergent selection experienced by subpopulations adapting to different habitats provide sufficient intrinsic premating isolation for sympatric speciation to occur. The initiation of speciation through a habitat shift in animals which mate within a preferred habitat (such as many phytophagous and parasitic invertebrates and some vertebrates, including birds) requires few genetic changes.