Genealogical trees of the drosophilids analyzed in the present work. a: general phylogeny; b: partial phylogeny of the melanogaster subgroup, an enlargement of the simulans/melanogaster branch of the upper tree. Numbers in panel a indicate how many million years ago the species diverged. The common ancestor of all these species is supposed to have lived some 60 million years ago; the divergence between D. melanogaster and D. tessieri probably occurred between 10 and 15 million years ago. The upper tree is partially taken and modified from . The lower tree is partially taken and modified from .