Written by: Stephen Hsu
Primary Source: Information Processing
Myers is both confused and insulting in his blog post, but I’ll refrain from ad hominem attacks, and just focus on the science.
Myers seems to think that humans with much better cognitive abilities than our own can’t exist. Sort of like a farmer in 1957 claiming that chickens that are bigger and faster maturing than his own could not exist (see figure below). I urge Myers to read some books on population genetics before returning to this discussion.
The argument for why there are probably genomes not very different from our own, but which lead to much better cognitive ability, is very simple, and I went through it in a post called Explain it to me like I’m five years old, excerpted below:
1. Cognitive ability is highly heritable. At least half the variance is genetic in origin.
2. It is influenced by many (probably thousands) of common variants (see GCTA estimates of heritability due to common SNPs). We know there are many because the fewer there are the larger the (average) individual effect size of each variant would have to be. But then the SNPs would be easy to detect with small sample size.
Recent studies with large sample sizes detected ~70 SNP hits, but would have detected many more if effect sizes were consistent with, e.g., only hundreds of causal variants in total.
[ Myers seems to be confused about the difference between specific (protein coding) genes, of which there may be only ~20k in the human genome, and the set of all variations in the DNA code, of which there are many, many more. Thousands of variants (or 10k) out of this much larger number is a tiny fraction much less than one. ]
3. Since these are common variants the probability of having the negative variant, with (-) effect on g score, is not small (e.g., like 10% or more).
4. So each individual is carrying around many hundreds (if not thousands) of (-) variants.
5. As long as effects are roughly additive, we know that changing ALL or MOST of these (-) variants into (+) variants would push an individual many standard deviations (SDs) above the population mean. Such an individual would be far beyond any historical figure in cognitive ability. [ This is exactly what has been accomplished via selection in the chickens below. ]
Given more details we can estimate the average number of (-) variants carried by individuals, and how many SDs are up for grabs from flipping (-) to (+). As is the case with most domesticated plants and animals, we expect that the existing variation in the population allows for many SDs of improvement (see figure below).
For references and more detailed explanation, see On the Genetic Architecture of Cognitive Ability and Other Complex Traits.
Attention PZ: The basic population genetics used above is recapitulated by famous geneticist James Crow (Wisconsin-Madison) here and here. You can take his word over mine, since I’m only a physicist. But note that Crow cites Feynman PhD student (i.e., theoretical physicist) Thomas Nagylaki (later a famous geneticist at Chicago) for proving a tour de force result in evolutionary genetics of additive traits. Do your HW next time.