mammalian success was founded on vegetarianism, and that vegetarianism was founded on microbes. Time and again, different groups of mammals swallowed plant-breaking microbes from their environments, and used their enzymes to mount assaults on leaves, shoots, stems, and twigs. It’s not enough to have the right microbes. They need room and time to work. Plant-eating mammals gave them both. They enlarged parts of their guts into fermentation chambers, partly to house their digestive comrades and partly to slow the passage of food so they could do their thing. In elephants, horses, rhinos,
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