There is an interesting new paper out on genetics and IQ. The claim is that they have found the missing heritability – in rare variants, generally different in each family.
Some of the variants, the ones we find with GWAS, are fairly common and fitness-neutral: the variant that slightly increases IQ confers the same fitness (or very close to the same) as the one that slightly decreases IQ – presumably because of other effects it has. If this weren’t the case, it would be impossible for both of the variants to remain common.
The rare variants that affect IQ will generally decrease IQ – and since pleiotropy is the norm, usually they’ll be deleterious in other ways as well. Genetic load.
This explains a few things. Studies have shown that people with high IQs are healthier and live longer. It doesn’t really look as if this was caused by smarter health decisions – so probably it’s because smart people, on average, have less genetic load. This explains why girls always run after the smartest guy in the room – at any rate it would explain that if it happened. It doesn’t.
There is a report of better sperm quality in high-IQ guys: that fits lower genetic load.
How does fit into observed IQ differences between groups? Well, selection could have favored IQ more in some places than others – or the mutation rate could have varied – or the efficiency of selection against deleterious mutations could have varied (more or less truncation-like) – or perhaps some mix of all three.
You could do an admixture analysis (how does IQ vary with different amounts of ancestry from group A and group B) without knowing the exact cause – it would still tell you if and to what extent racial genetic differences influenced IQ, even if you didn’t know the exact SNPs that made the difference.
In principle, you could get rid of the load by a kind of averaging process. More fun if the superman you create comes from way out in left field – say a super-Neanderthal, as I once suggested.
The rate at which new genetic load is generated, per generation, does not look to be too high (from the info we have), since the amount of observed IQ depression in the children of older fathers is, at this point, unobservably small.
If selection favors lower IQ, as it does today, you should see every IQ-negative allele increasing in frequency ( assuming that the side effects are not too awful): all of the GWAS fitness-neutral hits, and probably some of the mutational load alleles as well. You can be sure that the current dysgenic trend (~ 1 point drop per generation, not counting immigration) has not been operating too long, because if it had, we’d all be idiots, unable to read and understand past works of genius. Hasn’t happened. Michael Woodley and Bruce Charlton think so, but they are mistaken. Badly mistaken.