sciencehabit writes: Most male mammals wield a penis covered with spines made of keratin, the same material that forms fingernails, to sweep out competitors' sperm and irritate a female into ovulating. Even chimpanzees, our closest relatives, have penile spines. So why don't men? A new study suggests that this feature disappeared due to a chunk of DNA that went missing after our evolutionary divergence from chimps. The researchers have identified another DNA deletion that may have contributed to humans' bigger brains. Link to Original Source
I have yet to see any problem, however complicated, which, when
you looked at it in the right way, did not become still more complicated.
-- Poul Anderson