title: Genital evolution: cock-a-doodle-don't.
abstract: Losing the penis in species with internal fertilization may seem paradoxical, but birds have managed to do it multiple times. A new study addresses one developmental mechanism responsible for penis reduction in birds, and opens the door to further examination of this little understood evolutionary phenomenon.
authors.affiliation: Division of Organismal and Evolutionary Biology and Department of Biology, University of Massachusetts Amherst, Amherst, MA 01003, USA. pbrennan@bio.umass.edu
authors.forename: Patricia L R
authors.initials: PL
authors.lastname: Brennan
mesh_terms: D000818:Animals; D046090:Anseriformes / Q000196:embryology*; D055415:Bone Morphogenetic Protein 4 / Q000378:metabolism*; D046094:Galliformes / Q000196:embryology*; D008297:Male; D010413:Penis / Q000033:anatomy & histology*
chemical_list: D055415:Bone Morphogenetic Protein 4