For decades, people talked about “the gene for height”, “the gene for intelligence”, etc. Was the gene for intelligence on chromosome 6? Was it on the X chromosome? What happens if your baby doesn’t have the gene for intelligence? Can they still succeed?
Meanwhile, the responsible experts were saying traits might be determined by a two-digit number of genes. Human Genome Project leader Francis Collins estimated that there were “about twelve genes” for diabetes, and “all of them will be discovered in the next two years”. Quanta Magazine reminds us of a 1999 study which claimed that “perhaps more than fifteen genes” might contribute to autism. By the early 2000s, the American Psychological Association was a little more cautious, was saying intelligence might be linked to “dozens – if not hundreds” of genes.
The most recent estimate for how many genes are involved in complex traits like height or intelligence is approximately “all of them” – by the latest count, about twenty thousand. From this side of the veil, it all seems so obvious. It’s hard to remember back a mere twenty or thirty years ago, when people earnestly awaited “the gene for depression”. It’s hard to remember the studies powered to find genes that increased height by an inch or two. It’s hard to remember all the crappy p-hacked results that okay, we found the gene for extraversion, here it is! It’s hard to remember all the editorials in The Guardian about how since nobody had found the gene for IQ yet, genes don’t matter, science is fake, and Galileo was a witch.
And even remembering those times, they seem incomprehensible. Like, really? Only a few visionaries considered the hypothesis that the most complex and subtle of human traits might depend on more than one protein? Only the boldest revolutionaries dared to ask whether maybe cystic fibrosis was not the best model for the entirety of human experience?
Scott Alexander, “The Omnigenic Model As Metaphor For Life”, Slate Star Codex, 2018-09-13.
February 15, 2025
QotD: The absurdly high early expectations for genetic research
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