The evolution of the ass

Echidne has hilarious parody of the sort of 'reasoning' prevalent in evolutionary psychology. Go read her for the full context.

Maybe humans inherit big buttocks from their fathers, too? But why did this gene (if it exists in humans) survive? Here's where the scientific evolutionary psychology comes to my aid. The rules are something like this: Figure out how something that appears today might have once been useful, then explain its prevalence by the fact that it was once useful. It's a neat method, as lots of time is being saved by not having to go out to gather evidence or set up laboratory experiments, and it has the additional advantage (to me, at least) that nobody can prove my theory wrong. So here's my theory entitled 'How Buttocks Came to Be'.

A long time ago and far away lived a tribe of humans. Some of them were slender as a reed, and where we have buttocks they only had a small tight knot. Others had very large buttocks dragging behind them on the ground as they walked. Yet others were just right, not too slim and not too fat. Like we are.

Once a year the tribe would gather together for a mating ceremony in which all the men would fight each other for the right to inseminate all the females. (The females, as is common in evolutionary psychology in general, are going to be ignored from now on.) The mating ceremony took three days: On the first day all men would sit in a circle until they couldn't take it anymore. All those no longer sitting at sunset were discontinued. On the second day all remaining men would run around in a circle, nonstop, until the sun set. The fastest runner at this time would be declared the winner of the insemination ceremonies. The third day was spent on insemination.

Well, dear reader, you can guess what happened. None of the stick-figurelike knot guys could sit on the ground all day. They developed terrible sitting sores and despite firm determination and great stamina eventually had to admit defeat and get up just to get the blood moving again.

The really big-butted guys had a wonderful time with the first day's tournament. They could have easily sat for another week. But the next day they had to run and run, and as they ran their buttocks dragged behind, hit rocks and sticks and just hurt. Then they started bleeding. Besides, it's hard to run fast with something like that. However, valiant they were, these men, too, were disqualified. Only the fastest of the just-right guys got to pass his genes on.

And that's how buttocks came to be.