…the bad news is that they can't agree which one.

I explained the debate more here, but the short version is: twin studies find that most traits are at least 50% genetic, sometimes much more. But molecular studies - that is, attempts to find the precise genes responsible - usually only found enough genes for the traits to be ~10-20% genetic. The remaining 35% was dubbed "missing heritability". Nurturists argued that the twin studies must be wrong; hereditarians argued that missing effect must be in hard-to-find genes.

The latter seemed plausible because typical genetic studies only investigate the genes that most commonly vary across people - about 0.1% of the genome. Maybe the other 99.9% of genes, even though they rarely vary across people, are so numerous that even their tiny individual effects could add up to a large overall influence. There was no way to be sure, because variation in these genes was too rare to study effectively.

But as technology improved, funding increased, and questions about heredity became more pressing, geneticists finally set out to do the hard thing. They gathered full genomes - not just the 0.1% - from thousands of people, and applied a whole-genome analysis technique called GREML-WGS. The resulting study was published earlier this month as Estimation and mapping of the missing heritability of human phenotypes, by Wainschtein, Yengo, et al.

Partisans on both sides agree it's finally resolved the missing heritability debate, but they can't agree on what the resolution is.

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