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

by Nick Lane

Over the last few years, comparisons of large numbers of genes in more representative samples of species have come to the unequivocal conclusion that the host cell was in fact an archaeon – a cell from the domain Archaea. All archaea are prokaryotes. By definition, they don’t have a nucleus or sex or any of the other traits of complex life, including phagocytosis. In terms of its morphological complexity, the host cell must have had next to nothing. Then, somehow, it acquired the bacteria that went on to become mitochondria. Only then did it evolve all those complex traits. If so, the singular origin of complex life might have depended on the acquisition of mitochondria. They somehow triggered it. This radical proposition – complex life arose from a singular endosymbiosis between an archaeon host cell and the bacteria that became mitochondria – was predicted by the brilliantly intuitive and free-thinking evolutionary biologist Bill Martin, in 1998, on the basis of the extraordinary mosaic of genes in eukaryotic cells, a mosaic largely uncovered by Martin himself.