Why the Chicken Lost His Penis

Why did the chicken lose its penis? Turns out its a major development in evolutionary research.
Why did the chicken lose its penis? Turns out its a major development in evolutionary research.

Most birds, not just chickens, have no penis, and scientists have begun to ask the question of why. A recent study has revealed that as embryos, most birds do in fact have normally developing phallic members, however they have little to none by the time that adulthood is reached.

So why did the chicken lose his penis? It may sound like a terribly cliche joke, but this puzzling evolutionary tale is one that scientists think they have finally solved. Research has determined that the culprit responsible for the chicken losing his penis is a biological program that triggers cell death.

Dr. Martin Cohn, co-author of the study, explained that “Our discovery shows that reduction of the penis during bird evolution occurred by activation of a normal mechanism of programmed cell death in a new location, the tip of the emerging penis.” He also explains that it is thought that this process in turn gives the females more reproductive control.


This phenomenon may be a key piece in exploring evolution, as well as the biology responsible for causing birth defects according to University of Florida work published in this week’s Current Biology Weekly.

“One of the most puzzling events in evolution is the reduction and loss of the phallus in birds,” said Martin Cohn, A University of Florida biologist who studies the evolution of appendages. Evolution comes down to reproductive fitness. So it’s remarkable that a group of animals would eliminate a structure that’s so important for reproduction.”

Though there are some species of birds that have hung onto their penises through the evolutionary chain, about 97 percent of birds today are without their member. Birds such as the ostrich that have clung to their penis through time are typically lower on the evolutionary scale than those without.

The other penis-less birds use an opening referred to as cloaca to exchange the necessary bodily fluids for reproduction.

Although this subject may be one that is easy to laugh at, and probably wouldn’t be seen as a wise use of funds by the average person. This study intrigues evolutionary scientists who are seeking to explain why certain traits disappear from species through evolution. Birds lost the penis, while other land species have lost scales, tails, feathers, teeth, and many more traits as they adapted to new conditions.

Scientists have also used the gene Bmp4, which they found to be responsible for the causing the chicken to lose its penis. This gene is the one that shuts down phallic growth while the embryo is developing. Laboratory work has revealed that it is possible to stimulate phallic growth in mice through this gene, opening up plenty of doors in the medical world.

If we can now control the growth of a bodily member, the potential for birth defects, and male enhancement undoubtedly, are endless. Is it out of the realm of possibility to imagine this discovery being a way to solve missing limbs and other birth defects?

Discovery of the gene responsible for stopping growth of a member could provide a means to stop it. If we could simply turn of the switch responsible for stopping growth while the fetus was still developing, we could potentially stop the problem from ever existing.

So the mystery of why the chicken lost his penis has been solved, now if only we could figure out why he crossed the road.

Follow me on Twitter @CharlieGille

The Guardian Express

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