>>13105203There is good evidence that existing genetic variants in the human population (i.e., alleles affecting intelligence that are found today in the collective world population, but not necessarily in a single person) can be combined to produce a phenotype which is far beyond anything yet seen in human history.
Take the case of John von Neumann, widely regarded as one of the greatest intellects in the 20th century, and a famous polymath. He made fundamental contributions in mathematics, physics, nuclear weapons research, computer architecture, game theory and automata theory. In addition to his abstract reasoning ability, von Neumann had formidable powers of mental calculation and a photographic memory. Genotypes exist that correspond to phenotypes as far beyond von Neumann as he was beyond a normal human.
The quantitative argument for why there are many SD’s to be had from tuning genotypes is straightforward. Suppose variation in cognitive ability is 1. highly polygenic (i.e., controlled by N loci, where N is large, such as 10k), and 2. approximately linear (note the additive heritability of g is larger than the non-additive
part).
Then the population SD for the trait corresponds to an excess of roughly N^(1/2)vpositivevalleles (for simplicity we suppress dependence on minor allele frequency). A genius like von Neumann might be +6 SD, so would have roughly 6N^(1/2) more positive alleles than the average person (e.g.,?600 extra positive alleles if N = 10k). But there are roughly +N^(1/2) SDs in phenotype (?100 SDs in the case N ? 10k) to be had by an individual who has essentially all of the N positive alleles! As long as N^(1/2) >> 6, there is ample extant variation for selection to act on to produce a type superior to any that has existed before.
