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by the frequency he found in the U.K. Biobank, an anonymized research database: One in 7,000 people, according to his unpublished analysis, was born to parents who were first-degree relatives—a brother and a sister or a parent and a child.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 just a floor: It reflects only the cases that resulted in pregnancy, that did not end in miscarriage or abortion, and that led to the birth of a child who grew into an adult who volunteered for a research study.
Most of the people affected may never know about their parentage, but these days, many are stumbling into the truth after AncestryDNA and 23andMe tests.
I’ve been thinking it’s pretty common for a while, just because of how common a version of it with plausible deniability for the downsides (step siblings, etc.) is in porn. I know people say it’s just to appeal to people who really like it and the rest can just mute, but that’s very unconvincing. I always have porn muted, because the sounds don’t do much for me and just about every person I talk to about this (not a lot, so grain of salt) is surprised that anyone would mute as a rule. Secondly, I don’t think you really need words to pick up on the incest vibe.