Quoted By:
Eukaryotes-first may be called preposterous by people based on their gut, but the evidence we have does not support such claims. There is no reason that the first self-sufficient membrane bound organisms weren't more complex, and the bacteria simply decided to simplify their genomes and lose organelles, in favor of distributing the evolutionary gene-production method over a global collective. We just don't know, and it is wrong to buy into a political consensus, based on people's feelings (feelings which are usually uninformed by any picture of the complexity of the origin of life) when the evidence is not strong enough to support it unambiguously.
I tend to think that the first things you could call organisms were very diffuse, spread out over large regions, with no clear spatial localization, and certainly not bound to closed membranes. Then some organisms became selfish and packaged up a bunch of symbiotic membrane bound organelles into a functioning self-replicating Eukaryotic system, while others packaged themselves more compactly and maintained gene-sharing among the population, leading to the Eukaryotic/Prokaryotic split. This was around ~3 bn. years ago. This is a guess, but it's as good a guess as any.
The evidence for early eukaryotes is simply that the eukaryotes have a phylogenetic tree that goes back really far, I have seen estimates of 2.5 bn years for the common ancestor, and there is, as far as I know, no clear point where you have prokaryotes only.
