Scientists believe men once had small spines on their genitalia such as those found in chimpanzees, cats and mice.

Analysis of the genomes of humans, chimpanzees and macaques indicates that a DNA sequence thought to play a role in the production of these spines have been deleted in humans, but has been preserved in other primates. ...
http://www.bbc.co.uk/news/science-environment-12689692

And ladies across the world are very grateful. :D