OneAndOneIs2

There was a time in my life when I'd watch nature documentaries and see a lion or tiger taking down a wildebeest or some such, and wonder if maybe the theory of evolution had got it wrong.

Because evolution is supposed to favour sensible strategies, and yet what you basically saw was hundreds and hundreds of very large animals with long pointy horns run away from a handful of predators that were typically smaller than they were. This is like the entire British Army running away from half a dozen drunken teenagers. It just wouldn't happen.

You saw examples of how it could work when the lions went after the newborns, because often the whole herd will protect the young. And then suddenly instead of a herd of panicked bovines running in all directions, the lions might be faced instead with a wall of muscle and horns, and they generally suddenly remembered they had something else to be doing.

So why, I wondered, didn't they always do that? Why did they scatter and run if they knew they could face down the predators? It seemed counter to common sense.

And then some time later, I realised that this was the kind of fallacy that the phrase "Survival of the fittest" often leads to. It's the difference between the general and the specific.

For one specific wildebeest - the one the lions want to eat - it would be advantageous if the whole herd faced down predators. Obviously: It means that that wildebeest doesn't die.

But for the herd/species as a whole, it's actually the other way around: Lions don't go for the biggest, strongest, toughest animals. They go for the old, the sick, and the lame. Realistically, as a wildebeest, you have one of two states: You're either in pefect health, or you're being eaten by lions.

Think about the last few years: Remember all the hype about flu epidemics? Think how much less of an issue it would be if everybody who got laid up by flu was immediately eaten by a lion: No burden on the hospitals; much less risk of catching flu because there'd be far fewer sufferers.

Evolution tends to be quite heartless like that: It's strategies that are generally good but specifically bad that win. Unhealthy animals getting eaten by lions is bad for the individual animals but good for the species as a whole.

A problem comes when you remove that mechanism. Take diabetes - once, this was a fatal disease that caused a slow, nasty death. Now it's completely treatable. It's also far more common: As a treatable condition, it doesn't get removed from the gene pool the way it used to.

This is great in specific cases - the individual sufferer, who just has to faff around with insulin and measuring blood sugars instead of dying slowly. But not so good for the general case - the condition becomes more common.

The reason I mention all this is because my kitten, taken to the vet because of her bouts of diarrhea, has just been diagnosed with colitis. A very common ailment amongst cats and completely treatable.

The fact that it's treatable is what made it so common - see above.

So I blame Darwin for my recent vet's bill.

Hmph.