Here's How The Penis Evolved

Most of us aren't thinking about the evolution of the human anatomy or more specifically "private parts." Yet recent findings published in the journal Nature examine the evolution of the penis. Thanks to lizard limbs, the mystery is finally solved. 

"While mammal and reptile genitalia are not homologous in that they are derived from different tissue, they do share a 'deep homology' in that they are derived from the same genetic program and induced by the same ancestral set of molecular signals," said said lead study author Clifford Tabin, in a news release.

Harvard researchers discovered a link between the development of limbs in a variety of animals; they found that limb buds in snakes and "tail-but" tissue that eventually develops into the urinary and gut tracts are responsible.

Furthermore, when researchers transplanted a cloaca onto hind limb cells in a chicken embryo, it formed genital-like buds, according to Discovery. In reptiles, the cloaca is located near the hind limb tissues and is closer to the tail-bud--which helps explain why certain regions later support the development of external genitals.

"It demonstrates that there is a flexibility with what kind of cells can get recruited during development to form genitalia," added Clifford Tabin, via the BBC.

Furthermore, researchers note that their findings also illustrate just how much snakes have evolved over the last few years. While snakes used to have legs, they found that they likely evolved form a lizard that burrowed on either land or swam in the ocean.