Earlier today commenter “Mugabe” suggested the following thought experiment (I corrected a minor typo):

imagine you had 100 clones and each had been carried by a different gestational surrogate in a different country. and suppose there were 49 other such people like you in this regard.

i don’t find it hard to imagine that there would be norm crossing, that is, that the rank order would not be maintained across countries and that the smallest h^2 (calculated for a pair of countries) would be much smaller than .5.

I agree with Mugabe that in this scenario, the smallest heritability would be much less than 0.5, but I don’t think it matters because if HBD icon Arthur Jensen were alive, I have no doubt he would agree that on a global level, heritability is much lower than the 0.8 figure he liked to cite for countries like America.

The 0.8 correlation between middle aged identical twins raised apart (within countries like America) is controversial, not least because it implies an astonishing 80% of the variation in IQ is “explained” by genes. Taking the square root of the correlation implies that middle aged American IQ would correlate nearly 0.9 with genes! In other words, middle aged American IQ is nearly perfectly genetic.

But as Mugabe would argue, even if older American IQ correlates highly with genes, it doesn’t mean older American IQ is highly independently caused by genes. It could be that Tom has genes that code for an IQ of 120 in America but an IQ of 113 in Africa, and Bill’s genes code for an IQ of 120 in Africa and an IQ of 113 in America. So who is genetically smarter? Tom or Bill.

I have previously suggested that Mugabe’s thought experiment about a sample of people having many clones in many countries could be improved if the IQs of each person’s 100 clones (born from 100 different random wombs in a 100 different diverse countries) could be averaged, and this average would represent a person’s genetic intelligence. Since averaging each person’s 100 clones would cancel out the different reactions each genotype has to different environments, the higher the average IQ of your 100 international clones, the more independent causal high IQ genes or alleles you could claim to have (or the fewer low IQ causing genes/alleles).

So the real debunking of Jensenism would come not from showing that heritability for the entire world (or even just the developed world, or a particular range of countries) is less than 0.5 (no one disputes that), but rather from showing that less than 50% of the variation in older American IQ is independently caused by genes.

That is if a sample of 50+ random Americans each had 100 clones born in 100 random wombs in 100 random countries where they were raised in 100 random homes, and the IQ of each of these 50 Americans and each of their 100 random clones was tested at age 40; if the squared correlation between each American and the average IQ of his 100 clones was less than 0.5, only then could one say HBD and Jensenism have been debunked.