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NEW EVIDENCE FOR THE DECREASE OF THE GENOTYPIC INTELLIGENCE DURING HOLOCENE: A RECENT STUDY OF DAVID HILL

Iunie 29, 2017

David Hill republished, in 5 june 2017, an extremly interesting revised study in bioRxiv:

In Table 3 page 21, David Hill presents the variance of intelligence and education explained by minor alleles with different frequencies, that demonstrates different genetic architectures for the two complex traits, despite many authors use educational attainment as a proxy for intelligence.

The most interesting fact is that MAF 0.001-0.01 account for 44% of genotypic IQ and only for 33% of genotypic EDU. The MAF 0.001-0.01 have arose between 25,000 and 5,500 years ago (Zwick, 2001). There are much more MAF 0.001-0.01 that decrease than increase IQ and EDU. The very high percentage of variance explained by both of them could indicate a relaxed selection on the two traits since Last Glacial Maximum, and a relatively weaker selection on genotypic IQ than on genotypic EDU. This decrease of the selection parallels the decrease of brain size last 25,000 years (Ruff, 1997).

Another very interesting fact is that MAF 0.1-0.2 account for significantly less variance of IQ than all other MAF. MAF 0.1-0.2 arose between 325,000 and 200,000 years ago (Zwick, 2001), and their uniformly distribution in humans suggests this period was the period with the strongest selection on intelligence in humans. This is the period of emergence of Homo Sapiens. Also, brain size increased at 1450 cmc, larger than today brains. The penultimate place in explaining differences of IQ is occupied by MAF 0.01-0.1 (that arose between 200,000 and 25,000 years ago (Zwick, 2001)) suggesting during this period the selection on intelligence also was strong, and purifying selection uniformised the distribution of these MAF in humans.

Also, these MAF 0.01-0.1 and MAF 0.4-0.5 (that arose between 550,000 and 475,000 years ago (Zwick, 2001)) account for significantly less variance of EDU than all other MAF, suggesting between 200,000 and 25,000 years ago and between 550,000 and 475,000 years ago the selection for EDU was stronger than during other periods. Upper Palaeolithic selection on EDU is in line with the results of Racimo (2017), that found selection in East Asians before Holocene. Also, around 500,000 years ago emerged archaic humans, and brain sizes expanded from 900 cmc to 1300 cmc. Between 200,000 and 25,000 years ago there was strong selection on both EDU and IQ. During this period the brain size of humans peaked at 1600 cmc.

The lower decrease of selection on EDU than on IQ during Holocene could be explained if we admit that there are two types of variants that favor high-EDU: the first are shared variants that favor high-IQ, and the second are variants that favor high (self-)domestication of humans. Many of variants that favor high domestication favor low-IQ too. During Holocene variants that favor high-IQ decreased, and variants that favor low-IQ but high domestication increased. By this way, genotypic IQ decreased more than genotypic EDU during Holocene.

Concerning MAF younger than MAF studied by the article of David Hill, an older paper estimated that 81.4% of the rare protein-altering SNVs found in Americans with European origins originated in the last 5,000 years, and 14.4% of these SNVs are deleterious. 91.2% of the deleterious alleles originated in the last 5,000 years (Fu et al., 2013).

Although, Spain (2015) found fewer rare SNP in exome of people with very high IQ. Also, the IQ of superpopulations in 1000 GENOMES parallel the proportion of individuals that carry uncommon minor SNP (MAF frequency lower than 5%) in genes (Rao, 2017).

Probably future studies of David Hill will produce even stronger proofs for the decrease of genotypic intelligence since Palaeolithic period.

REFERENCES

Fu, W., O’Connor, T.D., Jun, G., Kang, H.M., Abecasis, G., Leal, S.M.,… & Akey, J.M. (2013). Analysis of 6,515 exomes reveals the recent origin of most human protein-coding variants. Nature 493: 216-220.

Hill, D.W. et al. (2017) Genomic analysis of family data reveals additional genetic effects on intelligence and personality. bioRxiv http://dx.doi.org/10.1101/106203

Racimo, F. et al (2017) Detecting polygenic adaptation in admixture graphs. bioRxiv doi: http://dx.doi.org/10.1101/146043

Rao, A.R. & Nelson, S.F. (2017) Calculating the statistical significance of rare variants causal for Mendelian and complex disorders. bioRxiv doi: http://dx.doi.org/10.1101/103218

Ruff, C.B., Trinkaus, E. & Holliday, T.V. (1997). Body mass and encephalisation in
Pleistocene Homo. Nature 387: 173-176.

Spain, S.L., Pedroso, I., Kadeva, N., Miller, M.B., Plomin, R. & Simpson, M.A. (2015). A genome-wide analysis of putative functional and exonic variation associated with extremely high intelligence. Molecular Psychiatry 21: 1145-1151.

Zwick, M.E. et al (2001) Genetic Variation Analysis of Neuropsychiatric Traits. in Methods in Genomic Neuroscience Chin, H.R., Moldin, S.O. (editors) CRC Press LLC

 

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