Tag Archives: Richard Klein

Polygenic IQ scores

15 Tuesday Oct 2019

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Commenter “Some Guy” had some questions about polygenic scores for me. His questions are in block quotes with my answers directly below each one.

How good do you think polygenic scores will have to get before they start getting used on an individual level? Like within how many SDs of the true IQ/g/educational achievement?

If one’s polygenic score is extreme enough, it doesn’t have to be very accurate at all to give useful information. For example, let’s say you have several embryos to choose from and one has a polygenic education score of +5 SD. Even though such scores only predict 12% of the variance, because +5 SD is so extreme, you can be about 97% confident that embryo will grow up to be more educated than the average person (assuming he or she is raised in a society similar to the one from which the stats were derived).

One problem with polygenic scores is they don’t seem translate well from one culture to another, suggesting they’re more correlative than causal.

The uses I can think of is to identify children with high potential from poor backgrounds, or as an environmentally unbiased entrance “exam” for schools etc.

What I would like to see them be used for is to estimate the IQs of historical Geniuses like Albert Einstein and to estimate the IQs of ancient human populations. For example Richard Klein believes there was a major genetic change in human cognition that occurred about 50 kya that allowed us to suddenly spread from Africa, replace the Neanderthals, colonize the globe and create representational art. If we compared the polygenic scores of humans both before and after the upper Paleolitic revolution, we could test this idea. Similarly Gregory Clark believes rapid genetic evolution in Europe allowed the industrial revolution.

I would also love to see polygenic IQ scores for the Neanderthals, assuming they would be meaningful in a group that culturally and genomically distinct.

What sort of PGS-IQ correlation would result in polygenic scores that are say within 1 SD of the true IQ? I know you often calculate standard errors from correlations, mind sharing the formula/method?

Within 1 SD with degree of certainty? If you mean with 95% certainty, you would need a correlation of 0.85+ which I doubt will ever be achieved. Even the correlation between two different IQ tests is seldom that high.

The method is to square the correlation to get the percentage of the variance explained, and then subtract that value from 1 to see what percentage is left unexplained.

So for example a PGS that correlated 0.85 with IQ explains 72% of the IQ variance, thus leaving 28% unexplained.

The variance is defined as the standard deviation squared, so since the IQ standard deviation is set at 15, the variance is 225, and 28% of 225 is 63.

The square root of 63 is 7.9 which is what the standard deviation would be if everyone had the same PGS. This is also known as the standard error of the estimate. Now in a bell curve, 95% fall within 1.96 of the mean, so multiplying 7.9 by 1.96 tells us that 95% of say the UK, will have IQs within 15.5 points of the PGS prediction.

So if you have a PGS of +2 SD that correlates 0.85 with IQ, your IQ will likely be 0.85(2) = +1.7 or IQ 126, with a 95% confidence interval of 111 to 142. But of course we’re nowhere near seeing a 0.85 correlation.

To get the general public to really trust polygenic scores for IQ, I’d guess the accuracy would have to be within 5 points of the true score. Within 10 points would lead to people who actually differ by 20 points regularly ending up with the same polygenic score. Since 20 points tend to be the difference between leaders and followers, such errors would be highly noticeable.

I think if they achieved a correlation of 0.7 with IQ they’d be considered credible (especially if the predictive power was maintained across oceans and generations). That’s the correlation between different IQ type tests with each-other and these are routinely used to decide issues as important as who gets into an elite college, who gets excluded from the military, who gets diagnosed as disabled or gifted, and who gets sentenced to death by the courts.

By the way, what do you think about this argument against people who consider intelligence entirely environmental: If that really was the case, then disadvantaged people would NEVER be smarter than people with good backgrounds. So why even bother giving people from poor backgrounds a chance? 100% environmentalism leads to un-egalitarian conclusions, and is easily disproven by the existence of smart disadvantage people.

It’s prima facie absurd, but it wouldn’t necessarily lead to the conclusion that we shouldn’t give deprived people a chance. On the contrary it might lead to the conclusion that changing IQ is simply a matter of changing environments.

The evolution of behavioral modernity

10 Friday May 2019

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Commenter Nehemiah writes:

It is implausible that the Bushmen populations (which once occupied a much larger range than today) lived in total isolation from non-Bushmen populations. Presumably the mutation or mutations that facilitated the emergence of grammar appeared or came together in one population first. This development was so valuable that the relevant genes had a high chance of being preserved and spreading to fixation if even a small amount of interbreeding occurred with a neighboring population. Thus, even if Bushmen (and Pygmies, BTW) split off between 200kya and 300kya, that would not have prevented the spread of an especially valuable mutation from any one human population to all the rest. I argue that a limited vocabulary already existed in all sapiens populations (and probably some non-Sapiens populations as well), but the appearance of the “grammar gene(s)” made vocabulary immensely more useful so that it was now worthwhile to coin many more words, and the more intelligent band members could master the use and comprehension of this expanding vocabulary much better than the less intelligent. The grammar mutation should have spread relatively rapidly from any human population to all the rest. If we backcrossed with Neanderthals and Denisovans, I cannot imagine that there was not also gene flow to (and from) Bushmen (and Pygmies) as well. Further, I know of no reason to presume that grammar did not first emerge in Bushmen and spread to non-Bushmen rather than vice versa. We simply do not know.

Neanderthals possessed our FOXP2 gene and a hyoid bone that facilitate speech, but the larynx was still in a more anterior position, as in an infant of our species, which restricted the number of vowel sounds that could be formed, and therefore the number of words that could be created. I argue that if Neanderthal has possessed grammatical language at an earlier date, there would have been evolutionary selection for a larynx positioned so that a larger number of words could be formed. Thus, I also argue that grammar evolved sometime after Neanderthals split from the lineage that led to sapiens, and our sudden and rapid colonization of the world in the last 70ky suggests that the grammatically structured use of vocabular evolved shortly before we exploded suddenly over the world’s surface, since the appearance of grammatical language is the most likely advantage that allowed us to expand rapidly and to quickly displace our rivals who were longer established and better adapted to the local environment.

The notion that a small number of genetic mutation(s) gave rise to behavioral modernity and the upper Paleothic revolution is associated with paleontologist Richard Klein:

But geneticist David Reich is having none of it:

Expanding our analysis to the whole genome, we could not find any location–apart from mitochondrial DNA and the Y chromosome, where all people living today share a common ancestor less than 320,000 years ago. This is a far longer time scale than the one required by Klein’s hypothesis. If Klein was right, it would be expected that there would be places in the genome, beyond mitochondrial DNA and the Y chromosome, where almost everyone shares a common ancestor within the last hundred thousand years. But these do not in fact seem to exist.

Our results do not completely rule out the hypothesis of a single critical genetic change. There is a small fraction of the genome that contains complicated sequences that are difficult to study and that was not included in our survey. But the key change, if it exists, is running out of places to hide….

From Who are we and how we got here by David Reich, pg 18

But while Reich largely rejects the idea of a single (or small number) of genetic mutations giving rise to behavior modernity, he seems open to the possibility that “…coordinated natural selection on combinations of many mutations simultaneously–did enable new cognitive capacities…”

See also: The importance of brain shape