Thinking aloud about engineering intelligence, again. There are two categories of alleles that affect intelligence: near-neutral SNPs that boost or decrease IQ, the things that make up the PRS score, and genetic load – uncommon, unfavorable mutations which everyone has some of.
Generally someone who is unusually intelligent has both more-than-average + PRS-type alleles and fewer-than-average unfavorable mutations. Having less genetic load is probably good in many ways ( up to a point). Having fewer unfavorable mutations (‘systems integrity’) may explain the longevity advantage we see.
If you have lots more PRS-type + alleles than average, you are probably going to do worse in some other traits. Neutral means there must be disadvantages associated with the advantages.
If you have enough PRS-type plus alleles and sufficiently few deleterious mutations, are way out on the curve, you’re going to end up with a phenotype that’s seldom or never been seen before, and has essentially never been tested by natural selection. Almost certainly something will go wrong. Same is true for height, although in that case we understand the failure modes better ( square-cube law, if nothing else).
Question: are some existing people already far enough out on the curve to begin to show signs of such problems?