The Vital Question: Why is life the way it is?

by Nick Lane

Martin predicted that complex life arose through a singular endosymbiosis between two cells only. He predicted that the host cell was an archaeon, lacking the baroque complexity of eukaryotic cells. He predicted that there never was an intermediate, simple eukaryotic cell, which lacked mitochondria; the acquisition of mitochondria and the origin of complex life was one and the same event. And he predicted that all the elaborate traits of complex cells, from the nucleus to sex to phagocytosis, evolved after the acquisition of mitochondria, in the context of that unique endosymbiosis. This is one of the finest insights in evolutionary biology, and deserves to be much better known. It would be, were it not so easily confounded with the serial endo-symbiosis theory (which we’ll see makes none of the same predictions). All of these explicit predictions have been borne out in full by genomic research over the past two decades. It’s a monument to the power of biochemical logic.