A new study, conducted by a team of scientists at the University of Florida, has successfully managed to unravel the mystery behind the underdeveloped penises in most bird species.
The culprit seems to be a single gene, which may be possibly enough to entirely dismember the penis in male birds, during the complex process of embryonic development.
While scientists already knew that around 97 percent of male birds do not have a significantly large penis; atleast not as large to deliver the sperm well inside the female reproductive tract, the actual cause behind that was virtually unknown.
This study, in particular, has helped shed light on how a single gene could so drastically impact development of the reproductive and/or other organs.
Led and co-authored by Dr Martin Cohn, this study has now been published in the journal Current Biology.
"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," Dr. Cohn explained.
On staining and closely monitoring the genital tubercle during embryonic development in chickens, the scientists found out that Bmp4, the gene which is supposedly responsible for causing the shrinking and underdevelopment of male penises in birds, starts to cause cell death in the 'penis' region after the ninth day of embryonic development.
Owing to the lack of the 'penetration' mode of reproduction, and the 'absence' of a developed penis, birds had to switch to another mode of reproduction, known as 'cloacal kiss.'
In such a mode of reproduction, both the male and female birds, which possess an orifice known as the cloaca, touch the cloaca together, and the male then transfers the sperm to the reproductive tract of the female.
Though the actual motive behind this loss of penis is not yet known, if revealed, it may help shed valuable insight on many other related questions, including why the snakes lost their limbs, and so on.
"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," Dr. Cohn added.
Was it an evolutionary attempt, or something else, only time will tell.