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On the one hand, according to the theory of gene-environment interaction, people who inherit certain traits tend to seek out life experiences that reinforce those characteristics. The most low-reactive kids, for example, court danger from the time they’re toddlers, so that by the time they grow up they don’t bat an eye at grown-up-sized risks. They “climb a few fences, become desensitized, and climb up on the roof,” the late psychologist David Lykken once explained in an Atlantic article. “They’ll have all sorts of experiences that other kids won’t. Chuck Yeager (the first pilot to break the sound barrier) could step down from the belly of the bomber into the rocketship and push the button not because he was born with that difference between him and me, but because for the previous thirty years his temperament impelled him to work his way up from climbing trees through increasing degrees of danger and excitement.
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