Two hypotheses have been proposed for the origin of insect wings. One
holds that wings evolved by modification of limb branches that were
already present in multibranched ancestral appendages and probably
functioned as gills. The second proposes that wings arose as novel
outgrowths of the body wall, not directly related to any pre-existing
limbs. If wings derive from dorsal structures of multibranched
appendages, we expect that some of their distinctive features will have
been built on genetic functions that were already present in the
structural progenitors of insect wings, and in homologous structures of
other arthropod limbs. We have isolated crustacean homologues of two
genes that have wing-specific functions in insects, pdm (nubbin) and
apterous. Their expression patterns support the hypothesis that insect
wings evolved from gill-like appendages that were already present in the
aquatic ancestors of both crustaceans and insects
