two men say they’re Jesus one of them must be wrong—Dire Straits
Historian Stephen Brush points out that the origin of the solar system remains unsolved because, though textbooks will dogmatically present the current theory, in fact the “current” theory seems to be changing on a regular basis. All the more so for evolution, which seems to be pivoting at an ever increasing rate. Consider the origin of the complicated eukaryotes. Practically every permutation has been suggested on the basic model of an ancestor splitting three ways to give rise to bacteria, archaea and eukaryotes. Perhaps the archaea split off from the eukaryote lineage, or perhaps the bacteria split off from the archaea lineage. Perhaps the bacteria split off from the eukaryote lineage, or perhaps the archaea and bacteria lineages produced a fusion that led to eukaryotes. For being an undeniable fact, it’s amazing how little evolution fits the facts.
Recently however, it seemed that at least some of this ambiguity was finally resolved. That finicky eukaryote lineage was finally nailed down for good. There was no question about it, the eukaryotes arose from a unique fusion event between a lonesome bacteria and archaea. Here is what I wrote just a few months ago:
I wish I had a nickel for every statement of evolutionary certainty that later had to be dropped. Carl Zimmer’s recent piece on how eukaryotes are supposed to have evolved quotes Eugene Koonin as stating that “it is certain” that a long time ago, in a warm pond far far away, two cells (an archaea and a bacteria) symbiotically merged to form the first eukaryote. The rest, as they say, was history, as from that humble eukaryote sprung everything from the trilobite to the tyrannosaurus.