The evolutionary history of the cell is shrouded in a past so distant and deep it has left few tangible traces of what early cells might have looked like and which processes may have gone on inside them. Hence, the study of cellular evolutionary history relies largely on inference. These inferences center on phylogenetic frameworks built with extant cells. Their traits are compared, and what we know about their biology is projected into the past. Phylogenetic trees are calibrated and constrained by fossils and geological events so that a sequence of evolutionary transitions can be inferred. Naturally, speculation and contention abound — which is part of the charm of this field.Florian Maderspacher, “The long dark teatime of the cell” at Current Biology
So cellular evolution is not the assured result of settled science, as we’ve all been told. Well, it certainly did sound more like a catfight over there. With a similar respect for facts. Further:
As with LUCA, inferring the nature of the common ancestor of eukaryotes is fraught with problems. On the one hand, the epochal merger — the engulfment of an alphaproteobacterium by the eukaryote ancestor — has the potential to make for a perfect kickstart to eukaryote evolution and complexification. Harnessing the aerobic energy-generation capability of this bacterium may have endowed the budding eukaryote with such a surplus of energy that it enabled a great expansion of genetic inventory, which in turn led to ever more complex cellular processes and structures. And these cells could grow and make a living by eating others. On the other hand, there is again a threshold of minimum complexity beyond which there are no bona fide living eukaryotes that are primitive enough so they could serve as models for important transitory forms (whatever we see as missing traits in eukaryotes is evidently due to secondary losses). This leaves us again with a conundrum in which the ancestor must have been already fairly complex — not least because it needed to be able to endocytose the bacterium — pushing back the problem of when eukaryotic complexity arose. But this time, somewhat of a deus ex machina came to the rescue — the discovery of an entirely new lineage of archaea.Florian Maderspacher, “The long dark teatime of the cell” at Current Biology
A deus ex machina is the intervention of a god in an ancient stage play. If these folks are here now, where will they be in a decade?