Vital Question: Energy, Evolution, and the Origins of Complex Life

by Nick Lane

The eukaryotic common ancestor might as well have jumped, fully formed, like Athena from the head of Zeus. We gain little insight into traits that arose before the common ancestor – essentially all of them. How and why did the nucleus evolve? What about sex? Why do virtually all eukaryotes have two sexes? Where did the extravagant internal membranes come from? How did the cytoskeleton become so dynamic and flexible? Why does sexual cell division (‘meiosis’) halve chromosome numbers by first doubling them up? Why do we age, get cancer, and die? For all its ingenuity, phylogenetics can tell us little about these central questions in biology. Almost all the genes involved (encoding so-called eukaryotic ‘signature proteins’) are not found in prokaryotes. And conversely, bacteria show practically no tendency to evolve any of these complex eukaryotic traits. There are no known evolutionary intermediates between the morphologically simple state of all prokaryotes and the disturbingly complex common ancestor of eukaryotes (Figure 6). All these attributes of complex life arose in a phylogenetic void, a black hole at the heart of biology.