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Comment by jackmott | Hacker News Reader

Knowing, in isolation, that IQ is more closely correlated with income levels in childhood than IQ is with thing X, does not imply that IQ is not a causal contributor of X.

It could just be the case that IQ is partly genetic (in fact, it is) and that IQ may be a causal factor in income levels to a stronger degree than it is for autism or other things.

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Hasn't IQ been proven to be not just partly, but mostly genetic? Barring exposure to outright toxic environmental conditions.

IQ has the highest genetic correlation out of any trait we've observed in Psychology - r ~ 0.7 if I recall correctly from my college days.

This is actually interesting in terms of GWAS - there used to be a large difference between "heritability" (~the measurable variance offspring shares with their parents, like height in cm, which can be influenced by a ton of parameters if you don't know about them/don't control them [like nutrition]). In the age of genome-wide association studies the linked SNPs often correlate much weaker than the heritability predicts (example: you could explain 10% of variance with SNPs, but heritability says it should be 70%) - this was called the problem of "missing heritability".

Some more complex models recover some of that missing heritability, these slides are a nice summary: http://jvanderw.une.edu.au/Mod9Lecture_SNP_Her.pdf

There is a paper from 2011 looking at human intelligence (http://www.nature.com/mp/journal/v16/n10/full/mp201185a.html) and using a little bit of modeling they got the correlation up high:

>We estimate that 40% of the variation in crystallized-type intelligence and 51% of the variation in fluid-type intelligence between individuals is accounted for by linkage disequilibrium between genotyped common SNP markers and unknown causal variants.

However, look at that "unknown", because the same abstract says:

>Finally, using just SNP data we predicted ~1% of the variance of crystallized and fluid cognitive phenotypes in an independent sample.

Using their SNPs alone it's only 1%. I assume the "true" genetic variability (~~~heritability) is somewhere in between those two values, since the 40/50% number seems to assume that these unknown variants will be discovered (they haven't yet AFAIK, maybe they don't exist, maybe they do).

Many of the studies showing this have some serious flaws, because of the types of people they tended to use. The twins used in the studies where disproportionately from higher income families. You don't find many low SES families who adopt, so for this and other reasons it's very difficult to find twins raised apart in low SES families.

The summary is that it's pretty clear that among higher SES families IQ is more than 50% genetic (but environment still plays a very large role). However, many studies indicate that among lower SES families, environment is the dominant factor.

There's still conflicting evidence here though, because there are some studies that indicate that SES has little impact on IQ heritability. The argument is that SES has a much greater on the heritability of IQ in children than on that of adults.

One idea that I ran across is that as SES rises, genetic contributions to success start to become the greatest factors.

Low SES environments are likely to cause malnourishment and other problems that cause people to fail to live up to their potential.

Thus, genetic explanations for inequality are more plausible among populations of high SES.

Right, and in fact this is known to be the case: http://biorxiv.org/content/early/2016/04/16/048991

My summary: https://brainslab.wordpress.com/2016/05/07/shared-genetic-co...

Right, but I wasn't trying to make the whole argument in one little post. The problem is that all our measures of intelligence have never been shown to be good measures. We've just sort of assumed that intelligence is a thing. When it fact it may be that any child who's provided with the resources and support to meet high expectations will meet them.

So what they could do here is show that Autism occurrence is more closely related to their measures than to income levels in childhood, but I don't think they did that (I confess I didn't read the whole thing).

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