> In 1975, around the time of Steve’s birth, a psychiatric textbook put the frequency of incest at one in a million. But this number is almost certainly a dramatic underestimate.
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The geneticist Jim Wilson, at the University of Edinburgh, was shocked by the frequency he found in the U.K. Biobank, an anonymized research database: One in 7,000 people, according to his unpublished analysis, was born to parents who were first-degree relatives—a brother and a sister or a parent and a child. “That’s way, way more than I think many people would ever imagine,” he told me. And this number is ju…