 In whatever way life began approximately 3.8 billion years ago, the first cells were something recognizably microbial, most probably bacterial. The next two billion years were also exclusively microbial, with Bacteria and Archaea manipulating the planet’s geochemistry to their own metabolic advantage, except when those unable to adjust to rising oxygen levels were wiped out by the cyanobacterial excretion of it. Another accidental consequence of microbial diversification was the formation of eukaryotic microbes, which fewer than a billion years ago diversified into the ancestral forms of the various multicellular groups we recognize today. Most of that diversification has in fact happened just in the last half billion years, in conjunction with ongoing microbial activities, hence Gould’s epithet.