Comments on my Previous Post

raised points that I thought it was worth spending another post on

One person linked to evidence of a correlation between head size and intelligence. Two pointed out a biological cost I had omitted, the difficulty in childbearing of getting a large head through the birth canal. That reminded me of an idea for a story I never wrote, involving a species of marsupial aliens. They knew that, because of the problem of getting a large head through the birth canal, only marsupials, who bring the baby out earlier and finish infant growth in their pouch, could evolve intelligence.¹ Observing Earth, they are puzzled as to where and why the intelligent marsupials responsible for skyscrapers and radio broadcasts are hiding.

There were three arguments in the comments, I think mistaken, each of which I got from multiple people.

One had to do with the nature of intelligence:

A significant part of what our culture calls "smart" is the ability to manipulate abstractions, to retain complex structures of abstractions and data, and to inhabit world models imaginatively—the sort of thing mathematicians excel at.

The obvious answer to your question, which every socially aware high school student could tell you, is that academic intelligence doesn't correlate with social awareness.

Nerds often lack basic social awareness. Cool men & women have more sex & therefore more children.

Being intelligent enough to understand and develop theoretical physics helps you not one bit to take down that woolly mammoth. For most of human history we needed street smarts and practical abilities.

This interpretation of my post may have been in part due to my use of “genius” in the title, which to many people suggests a particular form of intelligence, mathematical ability rather than the ability to run a firm or manipulate people. That was not my intent. Elon Musk is a genius. Barack Obama is very smart. My guess is that basketball stars are highly intelligent, though I have no data — they are doing a very complicated physical and tactical calculation in real time. It takes brains to be a successful con man, probably to succeed, even survive, as a Mafia capo.

Another argument:

I personally know a very ugly and not very smart woman who has 6 children. She's a sweet person, but . . .

… As long as such women can find men willing to mate with them Evolution is not at all 'selecting' for intelligence.

I researched dozens of brilliant intellectuals. Maybe up to a hundred. It is a clear pattern that their intellectuals pursuits in majority of cases are detrimental to their social and reproductive success.

I think across the world you see a pretty strong correlation that the lower intelligence you have, at least as long as you stay above retardation, the more kids you tend to have. Prisons and welfare offices are full of people with ten kids ten different parents by age 27 wheres your middle class HR office worker staff meeting, not so much. Trailer parks and ghettos are full of kids, upper middle class condos, not so much.

We are in a society so rich that even a not very successful woman can afford to bring lots of children to adulthood. We are also in a society with reliable contraception that lets people sacrifice the genes' objective to their own. Neither was true for most of our species history. So those observations, while they may be true, are not very informative for explaining the results of human evolution.

A third argument:

Human beings accomplish things as cooperative groups. It's very difficult to cooperate with people who are to different then you. In general, I think people communicate well within 1 SD of intelligence. Beyond 2 SD they find it very hard to understand.

Too smart and you go nuts: Being very smart and living with regular can be very difficult for some people; they often become sociopaths or weird hermits because of overwhelming sense of loneliness or otherness. That is really bad for reproductive success in societies where being very smart doesn't have exponential rewards as stark as it does today.

Smart people often can't conform well: Similar to the above, but smart people often notice that what people are doing is stupid and refuse to play along, and pay the price. Some societies don't have high prices for that, a smart person could become a priest or shaman or something, but some kill you.

If true, that implies that in a society with an average IQ of 100 an IQ of 150 may reduce instead of increase reproductive success. But as long as an IQ of 115 increases reproductive success, intelligence is being selected for and should increase. When the average gets to 115, 130 should increase reproductive success, and so on up. So although this is a reason why evolution might increase intelligence more slowly, it is neither a reason why it wouldn’t increase it nor an upper limit on how high it would eventually go.

One entertaining explanation of why we are not all geniuses, environmental rather than genetic:

I would also add: fluoride, glyphosate, aspartame, glutamates, BPA/BPS, Atrazine, chlorine, lead, GMOs, ethyl alcohol, whole language, and common core!

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Past posts, sorted by topic

A search bar for past posts and much of my other writing

1. Humans face a three way constraint. The infant has to be sufficiently developed to survive outside the womb. The woman’s pelvis has to be narrow enough to let her run. When an infant is born, its skull has to fit through the pelvis. We solve it by pushing on all three. Human infants are relatively premature compared to other species — compare a new-born baby to a new-born kitten. Women have wider pelvises than men and run less well. Human childbirth is more difficult than in other mammals — prior to modern medicine, death in childbirth was common, a few percent each time.

One implication is that the availability of caesarion section as an alternative to vaginal delivery should, ceteris paribus, lead to an increase in average intelligence.