“A very large mammal is living on the edge with respect to its reproductive rate,” he told me. “The gestation period of an elephant, for example, is twenty-two months. Elephants don’t have twins, and they don’t start to reproduce until they’re in their teens. So these are big, big constraints on how fast they can reproduce, even if everything is going really well. And the reason they’re able to exist at all is that when animals get to a certain size they escape from predation. They’re no longer vulnerable to being attacked. It’s a terrible strategy on the reproductive side, but it’s a great
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