Man, the Smooth Ape

How man 'lost his penile spines'. 

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.

It suggests another genetic deletion may have led to the expansion of specific regions of the human brain...

You thought I was going to talk about hair?  So why do Chimpanzees and other animals have them, and why (assuming our 4.5 million year old common ancestor had them too) did we lose them?

...Penile spines are barb-like structures found in many mammals. Their role remains under debate, and they may play different roles in different species.

They may increase stimulation for the male during mating. They might also play a part in inducing female ovulation in a small number of species, but there is evidence that they can cause damage to the female too.

Then there is the suggestion that they might have evolved to remove "mating plugs" - material that some male species deposit in the female genital tract to block other males' attempts to fertilise the same female...

You thought French Ticklers were a joke, didn't you?