Were it not for evolution, sex could be a pretty uncomfortable prospect. But fortunately for humans, the male penis evolved in one particularly nice way: it lost its spikes. Some animals, including chimps and mice, still have penises dotted with hard spines. But Stanford researchers have discovered one particular chunk of non-coding DNA that was lost, leading to the spine-free human penis. "Couples everywhere can be thankful that this particular piece of DNA was ditched," says a researcher.
The long-held belief is that the smooth human penis was the result of a more monogamous lifestyle; early ancestors’ penile spines may have been useful in removing the sperm of other suitors. The latest research did not set out to study this particular mystery, Nature notes; scientists were simply looking for chunks of DNA that the human genome, but not the chimp genome, had lost. Their discoveries also suggest similar molecular mechanisms for how humans evolved bigger brains and lost facial sensory whiskers. (Read more penis stories.)