And here we thought it was just our big brains: Since diverging from chimpanzees seven-million years ago, human ancestors lost several hundred DNA snippets that led to uniquely human traits—including tactile spines on our penises. Penis spines, like the ones found on chimpanzees, make the penis more sensitive and speed up sex. The loss of penile spines may have helped pave the way for monogamous sex in humans. In the end, it may still all be about our brains: The loss of some DNA may have allowed brains to grow larger.
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