Nick Lane

And the ones that got all the clean copies, they do all right.

The parent had got both the mutations and the clean copies.

But how do you distinguish between them?

Well, so it's about sampling, basically.

And uniparental inheritance, which is to say, it's a form of sampling.

You're taking the mitochondria only from one of the two parents.

So you're not mixing up mutations that both parents had.

You're kind of taking a subset.

So you're always increasing variance between the daughter cells.

And uniparental inheritance is basically giving you a subset.

These are the two fundamental... I mean, it's more complex.

But I mean, the thing about two sexes is you could say it's the worst of all possible worlds.

So again, if you kind of...

let's take it away from humans so we can be dispassionate about it.

You've got these single cells critters swimming around and they're all producing gametes and the gametes look the same as each other and they'll fuse in the same way as sex and they'll line up the chromosomes.

They basically do exactly the same thing that we do but on a single cell scale.

But having two sexes means that you can only mate with 50% of the population.

The other 50% is the same sex as you and is not going to accept your gametes.

If you had three sexes or four sexes, then you would be able to mate with a larger proportion of the population.

And some fungi...