I’m reading and listening to a book called “Adam’s Curse” by Bryan Sykes. It is such a shame that we can’t teach kids about sex, because it is mind-blowing.
OK, before you call the cops, child welfare, and Oprah on me, let me finish. The biology and evolution of sex is one of the most mind-blowing topics I’ve ever encountered. In fact, I’m convinced that this problem of teaching about sex is one of the sticky problems behind teaching evolution the way it should be taught. Maybe if we could talk openly about sex, more people would get it.
Evolution, I mean, not . . . oh, never mind.
Here’s what makes sex so mind-blowing (stop it!).
Why are there two different sexes? If you think about it from an efficiency point of view, it’s quite stupid.
We humans are members of a species that’s pretty much overrun the planet. You can’t swing a dead cat without hitting someone with whom you’re sexually compatible – well, at least genetically. But imagine for a moment you’re a member of a rarer species. Maybe a jaguar.
Jaguars are pretty well spread out in the jungle. Suppose you’re wandering about, looking for food and also a chance to mate. You catch the occasional monkey (hairy but good), but go days without seeing one of your own kind. Wait, there’s one! You go up to your new friend and – whoops, same gender as you. Back to the drawing board.
This will happen roughly 50% of the time. Seems pretty inefficient. Wouldn’t it be better if jaguars were all-purpose and unisex, so that any jaguar could mate with any other? Why this strange division?
(While we’re at it, why have sex at all? Sykes has an answer to this, too, and it might surprise you. Achoo!)
The answer, Sykes reveals, takes us back billions of years, to when we were all just single-celled creatures swimming about in some warm pond. Sex was an advantage, so we searched out the chance to blend our DNA with another’s through nucleus to nucleus sex.
The problem was that the nucleus, with all the juicy DNA we were after, was buried deep in the cell, with lots of cytoplasm in the way. While our nuclear DNA was eager to fuse with our mate’s, the cytoplasm wasn’t so excited about it. In animal cytoplasm are lots of creatures called mitochondria. Mitochondria were once free-living bacteria, but we co-opted them. Now they live in all our cells, and burn fuel using the oxygen we breathe. It’s mitochondria that make the dark meat dark in a Thanksgiving turkey, by the way. But that doesn’t have anything to do with sex.
Except it does, because mitochondria hate sex. It does them no good. They reproduce quite nicely without it, thank you, just splitting down the middle to make two mitochondria where once there was one. But if single-celled creatures start blending their DNA, they’re blending mitochondria, too. And mitochondria don’t like each other.
Whenever two cells come together like this, a war breaks out. The machinery in the cytoplasm of one cell starts destroying the mitochondria of the other, and vice versa. When it’s all over, one cell or the other has won, and only its mitochondria survive.
If it’s an even match, the cell is in big trouble. With few surviving mitochondria, the organism itself is unlikely to survive. So nature stacks the decks. Most sexual single-celled creatures come in two varieties. Sykes called them plus and minus. Plus is bigger, sometimes a lot bigger, and has lots more mitochondria. So that when the two cells have sex, the mitochondria of the plus win, and the minus mitochondria are utterly wiped out.
Since they always lose, anyway, it makes sense for the minus cells to get smaller and smaller. Why waste energy on mitochondria when all you’re going to do is deliver your DNA and die? The result is sex as we know it. Male sperm cells are tiny, with only two or three mitochondria to run the whippy tail. These are destroyed as soon as they go into the egg cell, while the precious DNA slips quietly into the nucleus of the egg, fertilizing it and making a little constitutional test case.
The consequences of this are staggering. Men (the descendents of the minus clan) can make lots and lots of sperm, because they’re so little (the sperm, not the men). Women (the plus descendents) can only make a few eggs. In our species, it’s even worse since pregnancy takes so long. From this split comes such unpleasant male attributes as promiscuity, aggression, and farting in public.
And that’s the mind-blowing stuff I wish we could teach kids. Sex is awesome!