Sexual Evolution: The Human Male

Humans and chimpanzees share more than 97% of DNA, but there are some fairly obvious differences in appearance, behavior and intellect. Now, scientists are learning more than ever about what makes us uniquely human.

We know that humans have larger brains and, within the brain, a larger angular gyrus, a region associated with abstract concepts. Also, male chimpanzees have smaller penises than humans, and their penises have spines. Not like porcupine needles or anything, but small pointy projections on the surface that basically make the organ bumpy.

Scientist have found that a switch that had been lost in humans that normally turns on an androgen receptor at the sites where sensory whiskers develop on the face and spines develop on the penis. Mice and many other animals have both of these characteristics, and humans do not.

"This switch controls the expression of a key gene that's required for the formation of these structures," said David Kingsley, a study co-author at Stanford University. "If you kill that gene, which has been done previously in mouse genetics, the whiskers don't grow as much and the penile spines fail to form at all."

Humans have kept the switch however -- we have androgen receptors, but ours don't produce whiskers or penile spines, he said. Chimpanzees do have small sensory whiskers, not as externally obvious as in cats or mice, but we don't have them at all.

Speculation abounds about what purpose the spines serve. One theory is that they are used in sperm competition; if the male's goal is to get his mate pregnant, he will want to take out her previous partner's sperm if she's recently had sex. The bumpy penis may be better for removing that sperm from the female, scientists theorize.

This sperm competition explanation is also consistent with shape of the normal human penis. The mushrooms shape has been selected for over millions of years to be adept at scooping out competitive semen.


Let's be honest here, the attractiveness of naked human male pales in comparison to our female counterparts and while getting laid can be hard enough for some (Read: Not me of course), God forbid, we get saddled with not only a unit with a mushroom cap, but really convenient spines too. Yeah, evolution, great job, that sounds awesome. That should help.