A study published on Wednesday by researchers at the Harvard Medical School in the journal Nature suggests that genitals developed from the same cells that created hind legs in lizards or that form the vestiges of limb buds in snakes.
At times when animals were first scrambling out of the water and taking over the land, limbs and lungs were required, apart from a new way of reproducing. As animals no longer had an aquatic environment to lay eggs, nature had to elegantly solve the problem, and while it may have had the same goal in mind, results weren’t always the same.
Crocodiles, birds and mammals, for instance developed one penis.
Lizards and snakes were luckier. They developed two.
It is only now that scientists begin to understand the common denominator between genitalia and limbs. The research team used biomedical technique to examine the genes that change during embryonic development and even resorted to Frankenstein-like surgeries to analyze whether surgically transplanting genital buds would allow them to form in unusual spots.
They found that in both mammals and birds, a set of cells located close to the tail area represent the place of genitalia formation. This development is deeply similar in all creatures, as basic genetic programming and signaling is responsible for these changes. What the team found is that this process is similar to limb formation and came to the conclusion that the evolutionary origins of genitalia and limbs must be common.
“It has been known in the medical field that babies that are born with malformations in their limbs often also have malformations in their genitalia,”
Patrick Tschopp said.
“We knew there was some sort of genetic link between the two, and this could provide some information about where these genetic links are.”
Tschopp and his team stumbled across an unusual aspect of limb formation while working on animal evolution. A colleague of his had been trying to understand whether snakes lacked the developmental mechanisms responsible for limb formation. When they noticed that the cellular program causing snakes to develop unusual, two-pronged genitalia was similar to how limbs developed, they decided to pursue the avenue.
They attempted to transplant the precursor of the gut in various positions and when they positioned it onto cells that typically give rise do hind limbs in chicken, they caused genital-like buds to arise.
“Our understanding of developmet of the external genitalia at the molecular genetic level lags years behind that of other organ systems,”
Martin Cohn, a researcher studying the same topic at the University of Florida, said.