Nick Lane: evaluation

Transcript context

…Why is it supposedly this hard to have this successful endosymbiotic event? There are multiple reasons. One of them is that prokaryotes, we should say archaea and bacteria, are pretty small things. 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. Once you’ve got these cells inside you, that may have happened on scores of occasions. There’s some tentative evidence that suggests it happened with archaea. There’s one nice example where the haloarchaea 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. The question is, how often would it go wrong and you lose your endosymbiont? I guess that would be the more likely outcome, that you pick up a bunch of genes and you lose your endosymbiont. It simply doesn’t work out. It’s hard to know exactly what all the bottlenecks are here. But there has been some modeling work done to see if 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? Under most conditions that these people have looked at there in Santa Fe, the answer is you do better if you’re not part of the symbiosis. Only under certain conditions will you do better. So predictably, the endpoint is that it doesn’t work. Given how many bacteria and archaea there are, throughout Earth’s history there are trillions, trillions, and trillions of these running around, there are many situations in which there was an endosymbiosis, and in only one case it succeeded. The odds would have to be remarkable. It would have to be extremely, extremely tough.…

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