Tuesday, December 8, 2020

Large differences at a few genes?

By equalizing the environment, socialist regimes made genetic influences more noticeable (Wikicommons).



Current thinking is that cognitive ability differs from one person to the next through small differences at very many genes.  This view is stated in a recent review of the genetics of intelligence:


It became clear that the problem was power: the largest effect sizes of associations between individual single-nucleotide polymorphisms (SNPs) and intelligence were extremely small, accounting for less than 0.05% of the variance of intelligence. The average effect size of the tens of thousands of SNPs needed to explain the 50% heritability of intelligence is of course much lower. If the average effect size is 0.005%, 10,000 such SNP associations would be needed to explain the 50% heritability of intelligence. (Plomin and von Stumm 2018)


This view is not shared by IQ researcher Volkmar Weiss, who argues that a few genes have variants that differ more substantially in their effects. Fortuitous combinations of such variants may explain the births of exceptionally intelligent individuals to above-average parents:


The possibility of rapid social ascent and descent suggests that the differences in thinking power, the IQ, are based on a simple genetic polymorphism, which prevents the solidification of society. A broad middle class, which marries upwards or downwards or among itself, connects the social extremes. The data supports it: The children of this middle class have a 25% chance of becoming part of the intellectual elite, 25% chance of belonging to the mentally healthy working class and a 50% chance of maintaining the social status of their parents. (Weiss 2020, p. 14)


Consequently, "in each generation the greatest number of highly gifted people do not come from marriages between highly gifted people, but from marriages of the middle class" (Weiss 2020, p. 13).


Weiss acknowledges that very many genes have some influence on cognitive ability, but in most cases the influence is secondary or tertiary. He argues that selection for intelligence, particularly in recent times, has operated mostly on a subset of genes with substantial effects. He cites a study by Davis et al. (2015) on the DUF1220 gene, which varies in the number of copies of a protein-coding sequence called CON2. Populations of European descent have 26 to 33 copies, and each additional copy is associated with a 3.3 point increase in IQ. Are there other genes with substantial effects on cognition? Perhaps.



IQ research in the DDR


Weiss grew up in East Germany and did his initial research on IQ there. He witnessed how the genetics of IQ, initially a taboo subject, became more and more acceptable in the socialist regimes of Eastern Europe. The authorities had made a systematic effort to erase class differences and equalize the social environment, only to find that differences in intellectual ability remained.  Indeed, by equalizing the environment, they had made the influence of genes more noticeable:


Contrary to the expectations of the Marxists, equal opportunities under favourable environmental conditions always lead to an increased genotype-phenotype correlation and thus to an increase in 'heredity'. ... This means that the better equal opportunities are guaranteed in an efficient educational system, the greater the variability of people based on genetic differences." (Mohr 1975, p. 48 [transl. by Weiss])


In the 1960s, and even more so in the 1970s, East Germany gave up its policy of preferentially admitting the children of workers or peasants to university … and thus preferentially hiring them for intellectually demanding jobs (Weiss 2020, pp. 44-45). The educational system now became oriented toward performance, with special classes for the highly gifted. Pragmatism was the keynote: the authorities wished to identify talented individuals and help them succeed. Academic research followed the same trend. In 1972, Weiss defended a doctoral dissertation in East Berlin on the inheritance of mathematical and technical abilities (Weiss 2020, p. 47).


On the eve of its dissolution, the Eastern bloc was learning lessons that the Western bloc had not yet learned … or had learned too long ago.





Davis, J. M., Searles, V. B., Anderson, N., Keeney, J., Raznahan, A., Horwood, J., Fergusson, D. M., Kennedy, M. A., Gledd, J. and J. M. Sikela. (2015). DUF1220 copy number is linearly associated with increased cognitive function as measured by total IQ and mathematical aptitude scores. Human Genetics 134: 67-75.



Mohr, H. (1975). Der prinzipielle Konflikt zwischen Biologie und Marxismus. In G. Szczesny (ed.). Marxismus, ernstgenommen: ein Universalsystem auf dem Prüfstand des Wissens. Reinbek bei Hamburg: Rowohlt pp. 30-50


Plomin, R., S. von Stumm. (2018). The new genetics of intelligence. Nature Reviews Genetics 19: 148-159. https://doi.org/10.1038/nrg.2017.104


Weiss, V. (2020). The Population Cycle that Drives Human History. Leipzig, Germany





Bruce said...

Occasionally you see a bright child born to relatively dull (or at least below average parents). Not the norm but not incredibly rare. Often there is a substantial difference in these individuals compared to siblings. It’s a roll of the (weighted) dice but the weighting isn’t uniform.

Sean said...

"each copy increase of CON2 was associated with a 3.3-point increase in WISC IQ (R 2 = 0.22, p = 0.045). In individuals from New Zealand, an increase in CON2 copy number was associated with an increase in math aptitude ability (R 2 = 0.10 p = 0.018)" Increase in copy number is also associated with brain growth and autism.

Christopher Badcock's theory is that such "duplications are enriched in individuals with autism and reciprocal deletions are enriched in those with schizophrenia.” Its all about genomic imprinting from mother or father. Mother's genes fight big brained baby, father's genes try and get the most out of the prenatal environment.

I have Plomin's book Blueprint, and he makes it clear he only very slowly and reluctantly came to the conclusion that many small genes were where the IQ action is, and almost quit out of disappointment. I would have to presume he knows what he is talking about. However if there are lots of particular locus big effect genes then CRISPR gene editing will become very much more practicable.

Sean said...

Bruce, I suppose a de novo copy number increase arising spontaneously in a relevant gene may help explain such an occurrence.