I think you should take seriously that in the first paper linked in my comment, the population-wide SNP heritability for cognitive ability is estimated at 0.24 and the within-sibship heritability at 0.14. This is very far from the 0.7 estimate from twin studies. While a perfect estimate of direct additive heritability would be higher than 0.14, I don’t think that rare variants (and gene-gene interactions, but this would no longer be additive heritability) would get you anywhere close to 0.7. Note also that UK Biobank with its purportedly poor IQ test represents only ~30% of the sample size in that paper.
Instead, I think it is becoming clear that traditional twin studies made overly strong assumptions about shared and non-shared environments, such that they over-estimated the contribution of genetics to all kinds of traits from height to blood creatinine concentration (compare gold-standard RDR estimates vs twin estimates here). As implied in my original comment, this is likely especially true for traits strongly mediated by society and behaviour. I find it somewhat counter-intuitive, but this kind of finding keeps cropping up again and again in papers that estimate direct heritability with the most current methods.
I’ll need to do a deep dive to understand the methods of the first paper, but isn’t this contradicted by the recent Tan et. al. paper you linked finding SNP heritability of 0.19 for both direct and population effects of intelligence (which matches Savage Jansen 2018)? They also found ~perfect LDSC correlation between direct and population effects, which would imply the direct and population SNP heritabilities are tagging the exact same genetic effects. (Also interesting that 0.19 is the exactly in the middle of 0.24 and 0.14, not sure what to make of that if anything).
I think you should take seriously that in the first paper linked in my comment, the population-wide SNP heritability for cognitive ability is estimated at 0.24 and the within-sibship heritability at 0.14. This is very far from the 0.7 estimate from twin studies. While a perfect estimate of direct additive heritability would be higher than 0.14, I don’t think that rare variants (and gene-gene interactions, but this would no longer be additive heritability) would get you anywhere close to 0.7. Note also that UK Biobank with its purportedly poor IQ test represents only ~30% of the sample size in that paper.
Instead, I think it is becoming clear that traditional twin studies made overly strong assumptions about shared and non-shared environments, such that they over-estimated the contribution of genetics to all kinds of traits from height to blood creatinine concentration (compare gold-standard RDR estimates vs twin estimates here). As implied in my original comment, this is likely especially true for traits strongly mediated by society and behaviour. I find it somewhat counter-intuitive, but this kind of finding keeps cropping up again and again in papers that estimate direct heritability with the most current methods.
I’ll need to do a deep dive to understand the methods of the first paper, but isn’t this contradicted by the recent Tan et. al. paper you linked finding SNP heritability of 0.19 for both direct and population effects of intelligence (which matches Savage Jansen 2018)? They also found ~perfect LDSC correlation between direct and population effects, which would imply the direct and population SNP heritabilities are tagging the exact same genetic effects. (Also interesting that 0.19 is the exactly in the middle of 0.24 and 0.14, not sure what to make of that if anything).