We now know that although genetic influences on height are very strong, no single allele accounts for much of the variance. We can say the same about intelligence: no single allele accounts for much of the variance. In fact, researchers are having to look at really large samples to find anything.
If you understood the effect of every allele, and if you could casually edit the entire genome, you could make smarter people – far smarter, probably, than anyone who has ever lived. But that would be hard. Personally, I prefer to find easy ways of doing things. Call me eccentric.
You see, there are single-gene changes that will make you considerably taller. Marfan syndrome makes you 5 or 6 inches taller than you would otherwise be. Pituitary tumors have stronger effects – giants can be over 8 feet tall.
Such mutations certainly have a large effect on height, but they don’t account for much of the variance, because they’re rare. And they stay rare because they’re bad for you.
There may well be mutations that have a large positive effect on IQ – but they must also be bad for you, else they would already be fairly common. ” Bad for you” means that on the whole this condition reduced fitness. Notice the past tense – reduced fitness in past conditions. People with Marfan syndrome used to have their aortas pop when they were about 45 – you can maybe see how that would reduce fitness. While giants were highly subject to the slings and arrows of outrageous fortune – especially the slings.
If you looked at people with truly extreme heights, all of them are due to rare, large-effect, deleterious mutations.
At least some of the people with the most extreme mathematical talent might have similar causes. A surprisingly large fraction of such mathletes seem quite odd. To those mathematicians who are about to claim that people in general are just as odd – you guys are really supposed to be able to count.
You could also look at an extreme population, ones that appears to have experienced strong selection for intelligence. Deleterious is relative: if we gave volleyball stars harems, Marfan syndrome would eventually become common.
And if we identify a mutation that significantly boosts intelligence [torsion dystonia?] , we may be able to make use of it – possibly by understanding the mechanism and mimicking it with some drug. Maybe we could deal with the negative side effects nowadays, or maybe we’d only use it on weekdays. I’d never do more than I really need.