If intelligence is such an important heritable trait, why isn’t everyone much smarter?

An interesting observation and argument from Variation In General Intelligence And Our Evolutionary History by Razib Khan.

If intelligence is such an important heritable trait, why isn’t everyone much smarter?

Think of this as the second Von Neumann paradox. What I’m alluding to is the fact that we know for a fact that human biology is capable of producing a god-made-flesh. With all due respect to another Jew who lived 2,000 years earlier than him, I speak here of John Von Neumann. We know that he is possible because he was. So why are the likes of Von Neumann bright comets amongst the dust of the stars of the common man, rather than the norm?

First, consider the case of Von Neumann himself. He had one daughter and two grandchildren. That is, within two generations genetically there was less “Von Neumann” than there had been. Though his abilities were clearly mentat-like, from the perspective of evolution Von Neumann was not a many sigma individual. He was within the normal range. Close to the median, a bit below in fecundity and fitness.

Taking a step back and focusing on aggregate populations, the fact that intelligence seems to be a quantitative trait that is at least moderately heritable and normally distributed due to polygenic variation tells us some things evolutionarily already. In Principles of Population Genetics is noted that heritable quantitative traits are often those where directional selection is not occurring due to huge consistent fitness differentials within the population.

Breaking it down, if being very smart was much, much, better than being of average smarts, then everyone would become very smart up to the physiological limit and heritable genetic variation would be removed from the population. Characteristics with huge implications for fitness tend not to be heritable because natural selection quickly expunges the deleterious alleles. The reason that fingerprints are highly heritable is that the variation genetically is not much impacted by natural selection.

The fact that being very intelligent is not evolutionarily clearly “good” seems ridiculousness to many people who think about these things. That’s because if you think about these things, you are probably very good at thinking, and no one wants to think that what they are good at is not evolutionarily very important. The thinking man cannot comprehend that thinking is not the apotheosis of what it is to be a man (similarly, the thinking religious man sometimes confuses theological rumination with the heights of spirituality; reality is that man does not know god through analysis, man experiences god).

Relates to an observation from Gregory Clark that perhaps Britain was the birthplace of the Industrial Revolution, with its dramatic increase in complexity and cognitive load, because, for a variety of reasons, Britain was one of the few places where the most accomplished families were among the most fecund. Upper class accomplished families displaced lower ability individuals at lower levels in the social strata. I.e. there was downward mobility from a social level, reflecting excess cognitive ability at the upper level.

But in most places at most times, it is hard to see in the historical record a substance selection pressure on exceptioanl cognitive capabilities. Indeed, it is easier to find examples of the opposite.