Everything (and everyone) alive today is descended from an organism that somehow survived the impact. But it does not follow from this that they (or we) are any better adapted. In times of extreme stress, the whole concept of fitness, at least in a Darwinian sense, loses its meaning: how could a creature be adapted, either well or ill, for conditions it has never before encountered in its entire evolutionary history? At such moments, what Paul Taylor, a paleontologist at London’s Natural History Museum, calls “the rules of the survival game” abruptly change. Traits that for many millions of
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