Male chickens lose phalluses before hatching
Some ducks have penises longer than their bodies, while chickens make do with a tiny bump. The vast size difference between the two types of fowl is due to a wave of cell death during chicken development, researchers report June 6 in Current Biology.
Although the ancestors of birds had penises, 97 percent of bird species have phalluses so small that they can’t insert into the female genitalia. Martin Cohn of the University of Florida and his colleagues found that in chick embryos, a gene turns on in the tip of the developing phallus, causing the cells to die and the tissue to wither away. In duck embryos, the gene does not turn on and the penis keeps on growing.