Babies with three parents

Originally posted by googlefudge
However the crucial bit is what happened next, ie the cell that was devoured not only
wasn't killed by, and didn't kill the cell that devoured it. And the two cells started dividing
together AND formed a symbiotic relationship.

What I meant was that whole process has happened many times.

http://en.wikipedia.org/wiki/Endosymbiotic_theory

I see also on Wikipedia that the cell nucleus may have arisen through a similar process.

Originally posted by googlefudge
One cell engulfing another is indeed common.

However the crucial bit is what happened next, ie the cell that was devoured not only
wasn't killed by, and didn't kill the cell that devoured it. And the two cells started dividing
together AND formed a symbiotic relationship.

This is why I think parasitism may have been the motivation (so to speak) of the mitochondrial ancestor. It is in the interests of the parasite that the host does not die. With a predation mechanism one needs to explain why the host cell did not devour the mitochondria. Of course the third possibility is that the relationship was always symbiotic, but initially with the mitochondria neighbouring the host cell, then attached and later still engulfed.

Originally posted by twhitehead
What I meant was that whole process has happened many times.

http://en.wikipedia.org/wiki/Endosymbiotic_theory

I see also on Wikipedia that the cell nucleus may have arisen through a similar process.

There are multiple chromosome pairs. Chromosome counts can change, but I don't see why this couldn't represent a sequence of mergers. A eukaryotic cell seems more of a community of organisms than one single unified one.

Where mDNA is different is that it is circular and does not require telomeres like nuclear DNA. So in that case quite different organisms underwent a merger, chromosomes are quite like each other.

Originally posted by twhitehead
What I meant was that whole process has happened many times.

http://en.wikipedia.org/wiki/Endosymbiotic_theory

I see also on Wikipedia that the cell nucleus may have arisen through a similar process.

Possibly the mechanism that allowed the assimilation of the proto-mitichondria more easily
facilitated the assimilation of other bacteria?

Once you have developed the tools to assimilate a bacteria and to synchronise it's reproduction
with yours, those mechanism might well make it easier to do so again, making subsequent
assimilations more probable?