I’ve always been fascinated by human evolution — by how, against all odds, our species became what it is today. Aside from simple curiosity, I cherish the faint hope that if we know who we are, we’ll be able to figure out how do deal with it all.

One of the striking facts of human evolution is that our ancestors adopted a bipedal gait (that is, walking on our hind legs) two or three million years before our brains started to get bigger. Numerous mammals, from bears to prairie dogs, will pop up on their hind legs to have a look around — the view is better when you’re taller. But a bipedal gait is inefficient, and retooling the mammalian skeletal structure for something so inefficient is not something evolution would do, unless there was a reason.

It couldn’t have been to free our hands for carrying tools, because in those dim and distant days we weren’t carrying any tools! The working of stone into tools was millions of years in the future.

I’ve never read an explanation for the bipedal experiment in a book on paleoanthropology, but I’ve got one. As far as I know, this is entirely my original idea. It may be wrong — lacking a working time machine, we can only guess, we’ll never know for sure. But it fits the facts, and it matches my understanding of how evolution works.

Many species engage in fitness displays. The male peacock has an enormous fan of tail feathers, which serve no purpose whatever except to advertise his good genes to female peacocks (peahens, I guess you’d call them). Male moose batter themselves silly headbutting other male moose — again, for no good reason except to prove their fitness to female moose. The winner in the headbutting contest gets to pass on his genes to the next generation; the loser doesn’t. That simple fact ensures that moose headbutting will continue unabated for as long as there are moose.

So let’s picture a band of our simian ancestors. They’re sitting around in the jungle, eating papaya and picking the lice out of one another’s pelts — and one day a young male is playing around. He tries running on his hind legs, just for kicks. And a couple of the young females notice. So the next day he decides he’ll show off to the females specifically by running on his hind legs. He manages to run halfway over to the next tree before he falls. He attracts, perhaps, a mild interest among the ladies.

The next day, five of the young males are competing to see who can run the farthest on their hind legs. One of them actually makes it clear to the next tree before he falls over. He’s feted as a hero — a ceremony over which we will draw a discreet curtain, as it involves congress of body parts.

At some point, and more likely at a dozen key points along the way, random mutations will have given rise to changes in the anthropoid skeletal structure that made it easier for those who possessed the mutation to run farther or faster on their hind legs. And each mutation will have been passed on to the next generation and the next generation and the next, because in each generation the males who could best manage the awkward bipedal gait would have their choice of females. They would sire lots of babies. The males who stumbled and fell down — not so many.

Fast-forward a hundred thousand years. Our ancestors are still no smarter than their cousins the chimps, but they have a very different skeletal structure. And in every single tribe, the young males compete in foot-races.

If you think this theory is too cynical, you might want to ask a pro athlete. I don’t know any pro athletes personally, but my strong impression is that, you know, the ladies are powerfully impressed by their ability to hit a ball with a stick, throw a ball through a hoop, or whatever. It would be very surprising to meet a male pro athlete who didn’t have plenty of opportunities to sire offspring.

Being human is a lot more complicated these days than running foot-races. Once the brain gets into the act … but that’s another story, for another time.

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