IQ is a single number, but intelligence is not a single thing, and the genetic component to intelligence is most emphatically not a single gene. The most recent studies identify scores of genetic variants that correlate en masse with better results in cognitive tests. These differences are in genes that we all have, and the cumulative variance appears to be the thing that correlates with performances in tests. The number of genes involved is likely to go up as the resolution of the genome gets sharper and the sample sizes get bigger. I would be unsurprised if the number of genetic variants
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