That’s “the PP rule”, in order to give credit. This is a speculative inference from an observation by Pumpkin Person.
I’m going to generalize this as follows: A polymorphic trait that contributes to a more general capability, but is not specifically useful for that task, will be most competitive at +1 SD. In effect, the most successful white American men in any enterprise requiring genetic fitness but not height, particularly, will form a bell curve around 6’2″ (+1 SD from the white American male average).
Insofar as a task selects for more than +1 SD of a trait in the highest performers, we should expect that the trait is particularly adaptive for the task. It stands to reason that the best height for a man is 6’2″, and the best IQ is 115, unless there’s selection bias to the contrary. Furthermore, we expect that the smartest or most successful white American men will form a bell curve around 6’2″, and vice versa. Taking a quick look at the heights of US presidents, this pattern matches. Recent presidents cluster around 6’2″ (+1 SD) whereas a century ago they clustered around 5’11” (+1 SD at the time).
This may not be correct, but it seems pretty good offhand.
I’m not sure why this would be the case, but here’s an idea: a polymorphic trait is like a statistical sample of the overall genome. Why +1 SD, I have no idea, it’s just a number I picked because 6’2″ is the most sexually attractive male height, as I understand it, and 115 IQ is the beginning of the IQ “sweet spot” between 115 and 130. If this explanation of statistical sampling is correct, then it should hold for environmental variables as well as genetic, in predicting the average phenotypes that are the most successful at some task.
A fun little implication of this is to note that if the college application process produces an average university student IQ of 115, it could be replaced by a system that selects students based on height without losing any validity. Because it is increasingly the case that the average student IQ is approaching 100, we must conclude there is no selection effort whatsoever because it isn’t operating better than a flipped coin.