A new study published in the journal Current Biology sheds more light on how birds, including chicken, lost their external genitalia.
The study was led by Martin Cohn, from Howard Hughes Medical Institute and the University of Florida, who grew embryos from chickens and ducks in order to track their penis growth.
The researchers found that while the development of penis starts normally in both ducks and chicken, a protein released by a gene known as Bmp4 halts the development and then regresses the growth in chicken while the penis continues to grow normally in ducks as the gene stays switched off.
"Genitalia are affected by birth defects more than almost any other organ. Dissecting the molecular basis of the naturally occurring variation generated by evolution can lead to discoveries of new mechanisms of embryonic development, some of which are totally unexpected. This allows us to not only understand how evolution works but also gain new insights into possible causes of malformations", Cohn said.