Why do Stupid People Exist?

David Friedman asks the question

Sep 09, 2024

Being smart is a good thing, it is possible to be smart — some people are — so why isn’t everybody?

He is asking from an evolutionary perspective why it is that stupid people exist. It is the same question that I asked about short males, like myself (or David Friedman). There I pointed out that with mean regression, tall males will tend to have offspring who are shorter than themselves. Similarly regression to the mean would happen with intelligence. I also wrote,

I would speculate that for many generations, evolution did not care much about your IQ. In the past few hundred years, with modern culture, IQ began to matter more.

The mean reversion story requires that there is a point at which too much of something is harmful. At some point, too much height is bad for a man’s survival. I think there is evidence for that. The skeleton becomes stressed and other problems arise when someone is extremely tall.

One would have to make a similar case concerning intelligence. That is, beyond some point, you tend to be worse off with a higher IQ.

Friedman offers three possible explanations: a smarter brain may require more energy, so there will be environments in which someone with a lesser brain is more likely to survive; a smarter brain may lead one to perceive advantages in not reproducing, so a lesser brain is more likely to reproduce; a smarter brain may be more fragile, so a lesser brain may be better able to withstand genetic or environmental adversity.

As for today, I read (mis-read?) Joseph Bronski as suggesting that the socialism of the welfare state takes away a lot of selection pressure that might otherwise have weeded out people with low intelligence or poor emotional makeup. And that this population is more likely to favor socialism, so there is a feedback loop operating.

Anyway, I think that all it takes for a society to continue to produce people without genius IQs is for there to be some point at which higher IQ actually reduces fitness on average. There are many ways that a high-IQ person could be more fragile. More of the brain works on abstract stuff, and so the person loses concrete skills (the proverbial absent-minded professor). Or the person becomes more of a cognitive specialist, lacking general wisdom.

If high-IQ brains are more fragile, then mean regression kicks in to forestall any tendency for everyone to become geniuses. Just as the son of a tall male is likely to be shorter than his father, the son of a genius male is likely to be less of a genius than in his father. There will be individual exceptions, of course, but statistically you are more likely to see mean regression.

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