Nick Lane

It's a beautiful thought.

It would be lovely if that was how the universe worked.

But what we know on Earth is that you have 2 billion years of stasis, and then this apparent singular event where Eukaryotes arose, and then another long gap before you get to animals.

And then if you roll back the clock 2 million years, there aren't any humans around either.

That's right.

We're just the icing.

Well, there's multiple reasons.

I mean, one of them is that prokaryotes, we should say archaea and bacteria, well, they're pretty small things.

So just having another cell inside you is already a difficult thing to do.

There are occasional phagocytes in bacteria that can engulf other cells, but it's pretty uncommon.

And once you've got these cells inside you, that may have happened scores of occasions.

There's some tentative evidence that suggests that archaea, I mean, there's one nice example where the halo archaea seem to have acquired more than a thousand bacterial genes from the same source, implying perhaps they had got an endosymbiont that they then lost later on.

So the question is, how often would it go wrong?

And you lose your endosymbiont.

And I guess that would be the more likely outcome is that you pick up a bunch of genes and you lose your endosymbiont.

It simply doesn't work out.

So it's hard to know exactly what are all the bottlenecks here.

But there have been some modeling work done to see, okay, you get an endosymbiont.

Are you going to grow faster if you don't have the endosymbiont or you do have the endosymbiont?

And if you're the endosymbiont, are you going to grow faster if you're outside or if you're inside?