For billions of years, microbes developed new ways of interacting with their environment and with one another. In doing so, they hit on a number of the molecular parts and tools to build bodies, though they used them for other purposes. A cause for the origin of bodies was also in place: by a billion years ago, microbes had learned to eat each other. There was a reason to build bodies, and the tools to do so were already there. Something was missing. That something was enough oxygen on the earth to support bodies. When the earth’s oxygen increased, bodies appeared everywhere. Life would never
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