Researchers at the University of Florida, USA have found the reason why more than 10,000 birds are gradually losing their penises.
The researchers looked at the embryonic development of land birds with penises, such as ducks, and birds without penises, such as chickens.
They discovered that these birds had a normal penis development process as fetuses. However, at the final stage of the process, a gene called Bmp4 develops, causing the penises of these species to gradually atrophy.
In birds with penises, this gene is inactive, giving their penises a chance to fully develop. It is thought that in waterfowl, the penis exists to keep sperm from being washed away by water.
“The genitals are one of the fastest evolving organs in animals, from mollusks to mammals,” said Martin Cohn from the Hughes Medical Institute and the University of Florida, USA.
Even without a penis, male birds can still mate with female birds through internal fertilization. Many scientists believe that perhaps losing their penis helps them effectively control their reproductive process.
