Commenter Race Realist informed me of Ken Richardson’s critique of Arthur Jensen’s genetic arguments. The critiques are as follows:
It is very worrying to find a simplistic ‘Mendelian’ model of independent and additive genes still being urged upon us by Jensen. The ‘genetic beanbag’ view is clung to because it furnishes the only paradigm in which Jensen and coworkers can work ‘genetically’. In particular, it furnishes the famous ‘expected’ correlations for relatives (e.g. monozygotic versus dizygotic twins) which form the basis of ‘heritability’ estimates, even though doubts about the model for complex characters have frequently been expressed (see e.g. Barton& Turelli 1989). Indeed, recent molecular biology has shown better than ever how genes for evolved characters have become intricately tied in with adaptable regulatory systems across the genome as a whole. Under these regulations, variable alleles can be utilised for common ends, or common alleles utilised for divergent ends, as developmental needs dictate. Up to 90% of genes are regulatory in function, and not structural alleles at all (Jensen’s claim that humans have 100,000 polymorphic genes seems ridiculous). Phenomena such as canalization, divergent epigenesis, exon-shuffling (which modifies gene-products to suit current developmental needs), and even developmental modification of gene-structures themselves, now make a nonsense of the idea of a one-to-one relationship between incremental accumulations of ‘good’ or ‘bad’ genes, and increments in a phenotype (see e.g. Rollo 1995). This makes the objective of most twin and adoption studies surrounding IQ a red herring, because it is attempting to ‘prove’ a genetic model that no one can seriously believe in.
Ken is technically correct, but so what? Nothing he said debunks the high correlation between your DNA and your IQ. So maybe the correlation is more about the parts of DNA that regulate the genes than about the genes themselves, but it’s all still predicted from your genome which is defined as your complete set of DNA, not genes only. So to quote Hillary Clinton:
As for whether DNA’s effect on complex traits is additive or not, the empirical evidence suggests that it largely is. As for whether DNA has an independent effect (causation) on complex traits, commenter Mug of Pee says we need to ask whether the same genetic predictors of phenotype hold across a wide range of environments around the World, and when it comes to a genomic predictor of height, it certainly does (though the predictor gets weaker on different continents)
Ken then states:
Jensen argues that g has evolved as a ‘fitness’ character. Yet it is the logic of natural selection that fitness characters come to display little if any genetic variation. This has been repeatedly confirmed in artificial selection experiments, and in the wild. The self-defeating logic of Jensen’s argument is obvious. Indeed, I find it amazing that, at the end of the twentieth century, complex, sophisticated edifices like this are being constructed on such patently erroneous foundations.
So by that logic, brain size and height should have little if any genetic variation since they too were fitness characteristics and yet the heritability for height is reportedly 0.7 and the heritability for brain size is reportedly similar. Now perhaps Ken would dismiss all heritability studies as invalid, but then on what basis can he cite the “genetic variation” found in “artificial selection experiments”?