There is one argument against the claim that the distribution of intelligence is different by race or gender that I have very rarely seen and have not discussed here — the claim that since there is no advantage to being stupid there is no reason why evolution would produce any stupid people.
Being intelligent enough to understand and develop theoretical physics helps you not one bit to take down that woolly mamoth. For most of human history we needed street smarts and practical abilities. It's only in modern times that abstract thinking has been of such great value relative to physical abilities. Who needs to be able to conceive of and construct water works when you live in an area of ample fresh water resources. Who needs to develop systems of agriculture or even cities when you live in a land of abundance for everyone all year round.
There may be particular forms of intelligence that were not valuable for reproductive success until recently, might not be at present. But street smarts are evidence of intelligence. Being smarter makes you better at practical abilities. Keeping alive and fed in a primitive society requires intelligence, as does persuading one or more women to bear your children, if you are a man, or finding and keeping a high quality mate, avoiding seduce and abandon tactics if you are a woman.
Gheghis Kahn was obviously "intelligent". But the particular kind of smarts he had isn't useful to building a first world Mongolian state.
Similarly Jews are very intelligent, but that advantage had a much lower advantage until very recently.
In fact it doesn't even have an evolutionary advantage at present! It has one to an extent in Israel, but in the west smart Jews have very low fertility.
Per Gregory Clark, NW European intelligence probably rose in the century before the Industrial Revolution because the existence of relatively market economies and relatively low levels of violence allowed intelligent Yeomen farmers and entrepreneurs to out reproduce others. Absent this incentive structure such a feedback loop doesn't develop.
"Gheghis Kahn was obviously "intelligent". But the particular kind of smarts he had isn't useful to building a first world Mongolian state."
I don't know if it is useful for that. But it was useful for him to father a very large number of children, which is what is relevant to the evolution of intelligence.
"Similarly Jews are very intelligent, but that advantage had a much lower advantage until very recently."
One explanation of Ashkenazi IQ is that religious scholars were high status, hence desirable sons in law for wealthy members of the Jewish community with daughters.
"which is what is relevant to the evolution of intelligence"
A certain kind of "intelligence". They aren't all the same. Africans are very intelligent at certain musical or dance improv, but can't build a nuclear reactor. The North Koreans can despite being hell on earth.
"religious scholars were high status"
I think this helped a lot. As a Catholic I think the celibate priesthood is a liability. Protestantism corrected this.
However, the jewish advantage goes beyond religious leaders. I think the fact that they are allowed to be "middle men" helped a lot with the evolution of Jewish IQ.
I am reading _The Goodness Paradox_ by Richard Wrangham and he comments that brain size has been increasing but then says ' Around 30,000 years ago brains started to become smaller. In Europe modern brains are some 10 to 30 percent smaller than those living 20,000 years earlier'. (Chapter 3, Human Domestication, page 63). His sources are this paper by Maciej Henneberg https://pubmed.ncbi.nlm.nih.gov/9750968/ and Robert Bednarik https://pubmed.ncbi.nlm.nih.gov/25440983/
Another factor that might be relevant is neuronal density and maybe suggests that evolutionary efficiency gains might be had via greater density in a smaller brain.
"The best fit between brain traits and degrees of intelligence among mammals is reached by a combination of the number of cortical neurons, neuron packing density, interneuronal distance and axonal conduction velocity—factors that determine general information processing capacity (IPC), as reflected by general intelligence. The highest IPC is found in humans, followed by the great apes, Old World and New World monkeys. The IPC of cetaceans and elephants is much lower because of a thin cortex, low neuron packing density and low axonal conduction velocity. By contrast, corvid and psittacid birds have very small and densely packed pallial neurons and relatively many neurons, which, despite very small brain volumes, might explain their high intelligence. "
Dicke U, Roth G. Neuronal factors determining high intelligence. Philos Trans R Soc Lond B Biol Sci. 2016 Jan 5;371(1685):20150180. doi: 10.1098/rstb.2015.0180. PMID: 26598734; PMCID: PMC4685590.
Great. Glad you enjoyed. Of course that is only one of many possible explanations. If you are interested in such things, apparently humans have also evolved a distinctive role for dopamine in our brains that may explain intelligence as well. https://pubmed.ncbi.nlm.nih.gov/10585240/ You may remember the topic of dopamine being tossed about here earlier this summer. Interestingly, to me at least, dopamine also has been studied in wee bitty bee brains able to produce their utopic eusocial societies, paragons of patterns of sustainable specialization and trade. Might smaller brains be consistent with a theory that humans are evolving in a eusocial direction? https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7746283/
That looks more linear than exponential to me, just eyeballing it.
But even before looking at the link I didn't expect to see any kind of S-curve or plateau. Wouldn't it be an implausible coincidence if the amount of intelligence humans need to invent agriculture and civilization required millions of years of evolution, but then we hit an intelligence maximum or equilibrium within a dozen millennia of that?
Well, not logarithmic, or fitting that "0" on the axis would have been quite a stretch, but it's certainly very nonlinear. Thank you for pointing that out.
I heard someone in a podcast, I think it was Greg Cochrane, say that many of the things intelligence is good for are public goods (inventions, discoveries, etc.). So, the evolutionary pressure to select for intelligence is not that strong.
There is also the literal problem of a woman having to squeeze a bigger skull out of her vagina, which is a constraint.
"Social Theory"
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.
Being a lone smart person has evolutionary drawbacks as well. Think Archimedes being slain by the Roman soldier because he couldn't read the social situation.
So, archimedes had low social intelligence. And, humans can keep growing after birth, so women don't necessarily have to give birth to babies with bigger brains.
If “just grow after birth” was all that was needed we wouldn’t already have these giant brains at birth that are difficult to squeeze out and babies that take forever to grow the rest of their body into those heads compared to most species.
Women( and men) were probably larger due to better nutrition. The world has been heading toward worse and worse malnutrition for the last few centuries due to censorship and other kinds of slow war tactics. Governments don't just attack each other. They also attack their own people. Nowadays, I see media outlets on earth constantly attacking raw milk and saturated fat. Government schools don't talk about the role played by micronutrients such as minerals and vitamins. Most people think macronutrients and ignore micronutrients. Ignorance of micronutrients is apparent among body builders who care more about nutrition than most people. Women who lived on traditional diet including raw milk had wider hips suitable for giving birth to babies. Nowadays, women have narrow hips unsuitable for giving birth, and doctors recommend C section even when women can handle natural birth. Narrow hips result from calcium deficiency caused by lack of calcium, phosphorus, vitamin A, vitamin D, or vitamin K2. Raw milk provides all of them adequately. Pasteurized milk is deficient in vitamins.
Women couldn't have evolved to give birth to smaller babies within a few hundred years. Humanity hasn't had enough time to adapt to this worldwide (malnutrition) propaganda campaigns aimed at reducing population on earth. The same calcium deficiency is also the primary reason for dental cavities.
When you are deficient in those nutrients, your teeth will lose protection from bacteria and foods in your mouth. Fluoride doesn't really protect your teeth, and drinking fluoride through tap water is like drinking sunscreen. You are supposed to coat your skin with sunscreen, not drink it. You can medically coat your teeth with fluoride at a dentist clinic, but that won't protect you from dental cativites. Nutrition and hygiene protect your teeth from dental cavities. Without nutrients, your teeth lose calcium over time. On the other hand, fluoride is a known neurotoxin used to kill mice. More fluoride in tap water results in lower IQ among people.
Humans need more time to adapt to depopulation pressure that manifests in various ways including malnutrition propagandas and fluoridated tap water.
World governments have been obsessed with reducing human population on earth for quite a while. They also push various wars we don't need.
I'm angry with immorality of the ruling class, but it will take a long time time to rectify this if it's even possible to stop them.
Another potential biological cost is size of the cranium at childbirth.
There is also potentially a social cost. Increased "intelligence" (i.e. analytical reasoning ability) presumably had sharply reduced payoffs in the distant ancestral past, because there were fewer ways to put it to productive use. But the drawbacks of an analytical mindset would have been as sharp as ever.
Long ago I had an idea for a story I never wrote, involving a species of marsupial aliens. One of the scientific facts they knew was that only marsupials could be intelligent, because of the problem you mention. They observe Earth, are puzzled as to where the intelligent species responsible for skyscrapers and radio broadcasts and such are hiding.
Related to "Reproductive cost" but not mentioned: there is an opportunity cost of seeking to mate with smarter partners. The harder it is to find and vet a genius partner (which, in particular, could have a large cost for those lower on the ladder), the more sense it makes to make the choice quicker and have more (non-zero) children with worse partners in the meantime.
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. But that kind of intelligence isn't a primary survival trait; people who have it aren't necessarily good at quick thinking in an emergency, for example. A society needs a healthy supply of people with street smarts (or bush smarts) to support a small number of intellectually smart people who can do specialized mental tasks.
Being able to learn algebra, or even calculus, if you have to, is not the same thing as being a mathematician. For that matter, I have my undergraduate degree in mathematics from a fairly rigorous school, but I'm not a mathematician.
In most cases, if you haven't been damaged with bad foods or bad chemicals or bad air, you can become a mathematician as long as you actually want to become one.
Some people are too stupid to become a mathematician or become rich because their brains were chemically or genetically damaged by something. People don't just become stupid for no reason.
Everything has a cause. In the past, people used to believe lung cancer had no cause, but they now know smoking is a major cause of lung cancer. Air pollution is a major cause of lung cancer.
If you drink too much fluoride in tap water, your IQ can go too low to become a mathematician. Drink clean water. Fluoride is a potent neurotoxin used to kill mice.
However, I don't recommend becoming a mathematician especially if you want to become rich. I want to be rich.
You don't need to be among the smartest human beings. You need to be among the smartest people in your village/tribe.
Relative differences in intelligence are magnified when you bring together in a single society/community humans whose ancestors were separated for thousands of years.
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.
Nerds & academics are social misfits.
As for why, the answer probably lies within biology, psychology, neurology.
The genes/neurons/etc. that collectively that make someone more intelligent usually also make them socially disabled & the genes/neurons/etc. that collectively make someone more cool/socially skilled, on average, don't correlate to intelligence.
(I avoid the term "wiring" because I don't know anyone who was born with wires in his head.)
If you want the data to back it up, ask Emily Kierkegaard.
I assume you are taking frequency of sex as a proxy for social awareness. But I find:
"This analysis suggests that intelligence has little effect on frequency of sex, and this does not differ for men and women."
In model 8 they are, I think, controlling for income. So I read the result as "Rich men who get no words correct have more sex than rich men who get words correct." Am I correct?
Biology is messy, and members of a species rarely all hit the same target on a metric, unless the quality is under immense selective pressure (e.g., fertility, ability to learn human language, lactose tolerance in infancy). Expecting everyone to come out the same height or IQ is a non-starter of a premise.
I don't buy #2, or at least I would buy it's inverse "why are we all not morons" as in retarded people tend to reproduce less but not the opposite. 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.
And I think that holds historically as well and I'd even go as far to say smart man gets his head bashed with a rock trying to negotiate while dumb man rapes and pillages his village at the behest of his average intelligent war chief. The reproductive advantage is simply not to overly ponder the future, take and breed who you want now, die young but your children will inherit the earth and maybe some of them might even be smarter on average since you raped the nunnery and nobility too. Smart guys are killed in war, the average low IQ winner or even lower IQ civilian who couldn't even make it into a press gang repopulates the losers lands.
You are generalizing from a society so rich that even poor people can afford to rear ten kids to adulthood. That is not the environment our species evolved in.
I would add a few options that overlap some with yours:
Good enough is good enough: the returns for intelligence are diminishing, and often being pretty smart and having access to allies who are very smart is just as good as being very smart yourself. Selection effects for individual intelligence are thus not terribly strong, so wider variety is workable.
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.
Very smart people often find mental pursuits more interesting than physical: People who put mating and other status games at a lower priority relative to curiosity and mental pursuits are going to do less well.
So all together, if smart enough to get by is the common feature, the norm that society conforms to, very smart people are going to be selected against somewhat if they do not conform or successfully compete in the status and mating games of their group due to conflicting interests. Being less intelligent is not necessarily selected against if there are smart people you can ally with to take advantage of their cleverness through advice or trade, etc. Excess intelligence that alienates from others in the group tends to be a big problem, especially in the face of low returns on intelligence compared to today.
I would also throw in that intelligence seems to have very sharply diminishing returns when social rank is relatively fixed. A hunter gatherer tribe member might not have strong returns to intelligence, but a medieval serf might have somewhat negative returns. The serf doesn't get to plan improvements to his land, or decide different ways to plant, or get to run off and become a merchant or architect; in fact any impulse to do so might get him in a lot of trouble or dead. As a result, intelligence above a certain level is probably actively selected against as someone who finds a life of farming excruciatingly boring is likely to get himself killed. A certain lack of imagination and willingness to just accept a bad situation is probably good for living long enough to reproduce.
I think you are mistaken about the medieval serf. He does decide how to run his farm, and you may be underestimating how much intelligence is involved in doing so. At least after the 14th c. running off to do something else was an option — "City air makes free."
Fair point, I was over generalizing a good bit. I think it is true that he doesn't get to plan improvements to his land, because it is not his land to improve and so is limited to what the landowner will do or allow. I am also fairly certain he couldn't plan to say raise pigs suddenly if he was supposed to be growing flax and wheat. Depending on where one was and the legal framework of the time, however, there are probably big swings in autonomy and the returns to decision making and thought, you are correct.
While I agree that a level of intelligence is needed for farming it is worth keeping in mind that for much of the time it is pretty dull. After the planting there is not a lot to do other than keep birds and animals from nibbling the crop and weeding, which is why kids and wives were usually left to it while the men went off to raid and fight during the summer months. Harvesting is long, dull work. Planting is long, dull work. Some people might find it pleasant, but like the people who find cost accounting pleasant they are no doubt a small minority. Further, when most of your crop goes to someone else there isn't much incentive to apply your brain hard to the problem of getting more grown, either. I suspect there is a reason that for centuries the pattern was the smart children left the small farm for the city. It just wasn't the sort of environment that a very smart person could find interesting for very long, and the percentage of people who find that sort of thing interesting or pleasant is a small percentage of the population compared to the percentage of the population who did it for a living.
Related to this, and the laws in a time and place aspect, I recall reading that 18th c. Russian peasants (near slaves in places) were considered to be remarkably dull by western (British and French) soldiers that encountered them in the Crimean War, as compared to British and French peasants. No doubt there is a lot of jingoism there, but it tracks with the notion that harsh regimes with near zero social mobility tend to breed people selected for putting up with bad stuff and a certain lack of imagination for expecting better.
"Further, when most of your crop goes to someone else"
I think you have a somewhat distorted picture of the medieval system. Checking online for feudal dues, I find "in most cases, it was up to 30% of the harvest." Typically the peasant owned his own land but owed feudal dues on it, rent set by custom not free bargaining, might also owe some labor on the lord's land.
Again, differences in time, place and custom, as well as the distinction between serfs and peasants, are going to be relevant.
I do note that many serfs had the obligation to work 1/3 or 1/2 the days on their manor's fields instead of their own. If that is in addition to the up to 30% rate on gross production, that is a very steep tax rate. Also don't forget the church gets its cut (10%) along with anything else. But I can go with "much of your crop" instead of "most".
What tax rate do you think is sufficient to push people away from working harder to invest in more output vs engaging in more leisure?
And what do you believe the expected (or observed) rate of return on investment in improved farming practices to be to the average medieval serf?
How much does an extra point of IQ change that?
Those seem to be the key questions.
Serfs also only kind of owned their land, again with variances for time and place, with the landlord being the owner and the serfs having rights to live and work the land. How much any of that would track with our modern concepts of ownership is vague(there are arguments about whether US citizens own land vs the US government owning the land and we merely own the rights to use it for somethings), but it wasn't clearly fully owned by the serf.
Getting all this back to the point of its effects on IQ in an evolutionary sense, we would need to ask what a substantially higher IQ would do to benefit a serf. (Remembering that for quite a while that was a very large proportion of the population.) Using high IQ to figure out farming is non-trivial; the green revolution took forever because agriculture is complicated above a certain level, has very long cycle times on feed back(especially in colder climates), and if you are close to starvation screwing up experiments is really expensive. So people tend to apply a lot of shared knowledge and inherited wisdom (which doesn't require much IQ for the individual, just the existence of some smart people). If you are high IQ you can't stand on the shoulders of giants by doing research because it isn't available, you can only stand on the same shoulders as everyone else. You can do your own experiments and pay lots of attention, and that probably helps a bit, but it has long cycle times (one harvest per year) and many outside variables you can't control. If you increase crop yield by a crazy high 10% you get to keep 7%, and hopefully none of those outside factors diminish the output such that you hardly notice that you had a big increase. (E.g. your novel irrigation helps a lot, but plant disease and hungry birds are worse this year and your crop only improves by a tiny bit, making it hard to tell whether it worked.)
Plus the higher IQ person has to avoid the common higher IQ mistake of "This is totally going to work, I am going all in!... whoops" and killing themselves. Thinking you are smarter than everyone else and therefore aren't wrong is a common trap for people who are actually smarter than everyone else.
Throwing in another "in addition" category, if wealth isn't the only source of reproductive success, there are other avenues that IQ might not be selected for after a certain level. If people care about status, not just "the wealthiest serf" sort of status matters, but also "the biggest and strongest" or "the best at shooting a bow" or whatever. Not all of that is going to be highly correlated with intellect, and much of it might be negatively correlated. If I have to choose between between potentially increasing crop output through hard mental work or screwing around with my friends at playing whatever local game is high status, for instance, a smarter person might focus on crop output and be a little richer, while a dumber person might say "eh, good enough is good enough" and focus instead on being the best footballer. It is not clear ex ante that one will be more reproductively successful.
The comments are fun. But don't forget that high intelligence is also frequently distractable. And high intelligence doesn't win all 'contests' that might lead to reproductive success.
I personally know a very ugly and not very smart woman who has 6 children. She's a sweet person, but . . .
The 6 children have at least 3 different fathers and in all likelihood all would test at or just below 100 IQ. As long as such women can find men willing to mate with them Evolution is not at all 'selecting' for intelligence. And as my sainted grandmother used to say, "Men are dogs, and some of them would (mate with) a knothole in a wooden fence."
Evolution rewards whatever makes/allows you end up with grandchildren, preferably many grandchildren.
Also, in mt experience (I have no data at all), many high IQ males don't seem especially interested in sex at all. The highest IQ women I know at least seem to seek high IQ, successful (in one field or another) males, but may not have children.
We are in a very rich society in which even a not very successful woman can afford to bring lots of children to adulthood, also a society with reliable contraception to let people sacrifice the genes' objective to their own. Neither was true for most of our species history. So your observations, while they may be true, are not very informative for explaining the results of human evolution.
Sure, but prior to us becoming rich we also were still basically small groups for millennia where having living children was a group goal, so the societal pressure was in line with maximizing the number of offspring from all women, roughly speaking. Another set of hands, even at age 4 to 5 was a benefit.
Also, it's likely, I think, that IQ in general was held down due to lack of quality nutrition, and disease, variables which persisted well into the 20th century in the US. Even a really good hunter married to a really good gather might still not have necessarily always been able to provide good nutrition.
High IQ is not always as important as other qualities, so the evolutionary pressure is probably not as great as one might imagine as on the single variables. Nature's motto seems to be, "If it works, it works, and anthing that produces offspring must be working."
For if everyone were a genius, there would be no genius; it is a relative concept, like any other concept. Take the term "human"; there must be non-humans for such a term to have any use or meaning. So to speak, difference is the a priori of any concept; if there is a concept, it is already decided.
I would also add: fluoride, glyphosate, aspartame, glutamates, BPA/BPS, Atrazine, chlorine, lead, GMOs, ethyl alcohol, whole language, and common core!
Being intelligent enough to understand and develop theoretical physics helps you not one bit to take down that woolly mamoth. For most of human history we needed street smarts and practical abilities. It's only in modern times that abstract thinking has been of such great value relative to physical abilities. Who needs to be able to conceive of and construct water works when you live in an area of ample fresh water resources. Who needs to develop systems of agriculture or even cities when you live in a land of abundance for everyone all year round.
There may be particular forms of intelligence that were not valuable for reproductive success until recently, might not be at present. But street smarts are evidence of intelligence. Being smarter makes you better at practical abilities. Keeping alive and fed in a primitive society requires intelligence, as does persuading one or more women to bear your children, if you are a man, or finding and keeping a high quality mate, avoiding seduce and abandon tactics if you are a woman.
Gheghis Kahn was obviously "intelligent". But the particular kind of smarts he had isn't useful to building a first world Mongolian state.
Similarly Jews are very intelligent, but that advantage had a much lower advantage until very recently.
In fact it doesn't even have an evolutionary advantage at present! It has one to an extent in Israel, but in the west smart Jews have very low fertility.
Per Gregory Clark, NW European intelligence probably rose in the century before the Industrial Revolution because the existence of relatively market economies and relatively low levels of violence allowed intelligent Yeomen farmers and entrepreneurs to out reproduce others. Absent this incentive structure such a feedback loop doesn't develop.
"Gheghis Kahn was obviously "intelligent". But the particular kind of smarts he had isn't useful to building a first world Mongolian state."
I don't know if it is useful for that. But it was useful for him to father a very large number of children, which is what is relevant to the evolution of intelligence.
"Similarly Jews are very intelligent, but that advantage had a much lower advantage until very recently."
One explanation of Ashkenazi IQ is that religious scholars were high status, hence desirable sons in law for wealthy members of the Jewish community with daughters.
"which is what is relevant to the evolution of intelligence"
A certain kind of "intelligence". They aren't all the same. Africans are very intelligent at certain musical or dance improv, but can't build a nuclear reactor. The North Koreans can despite being hell on earth.
"religious scholars were high status"
I think this helped a lot. As a Catholic I think the celibate priesthood is a liability. Protestantism corrected this.
However, the jewish advantage goes beyond religious leaders. I think the fact that they are allowed to be "middle men" helped a lot with the evolution of Jewish IQ.
Spoken like a man who has never shot a coilgun at an elephant.
The premise of this post is wrong because humans are not in an evolutionary equilibrium (and haven't been for millions of years). Hominid brain size has been increasing exponentially for at least three million years. (https://www.researchgate.net/figure/A-crude-plot-of-average-hominid-brain-sizes-over-time-Although-after-an-initial_fig2_265057343)
So evolution is making humans as smart as possible and some of us are just farther along that evolutionary path than others.
I am reading _The Goodness Paradox_ by Richard Wrangham and he comments that brain size has been increasing but then says ' Around 30,000 years ago brains started to become smaller. In Europe modern brains are some 10 to 30 percent smaller than those living 20,000 years earlier'. (Chapter 3, Human Domestication, page 63). His sources are this paper by Maciej Henneberg https://pubmed.ncbi.nlm.nih.gov/9750968/ and Robert Bednarik https://pubmed.ncbi.nlm.nih.gov/25440983/
Another factor that might be relevant is neuronal density and maybe suggests that evolutionary efficiency gains might be had via greater density in a smaller brain.
"The best fit between brain traits and degrees of intelligence among mammals is reached by a combination of the number of cortical neurons, neuron packing density, interneuronal distance and axonal conduction velocity—factors that determine general information processing capacity (IPC), as reflected by general intelligence. The highest IPC is found in humans, followed by the great apes, Old World and New World monkeys. The IPC of cetaceans and elephants is much lower because of a thin cortex, low neuron packing density and low axonal conduction velocity. By contrast, corvid and psittacid birds have very small and densely packed pallial neurons and relatively many neurons, which, despite very small brain volumes, might explain their high intelligence. "
Dicke U, Roth G. Neuronal factors determining high intelligence. Philos Trans R Soc Lond B Biol Sci. 2016 Jan 5;371(1685):20150180. doi: 10.1098/rstb.2015.0180. PMID: 26598734; PMCID: PMC4685590.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4685590/
Oh, cool paper that I also have never heard of.
Thank you!
Great. Glad you enjoyed. Of course that is only one of many possible explanations. If you are interested in such things, apparently humans have also evolved a distinctive role for dopamine in our brains that may explain intelligence as well. https://pubmed.ncbi.nlm.nih.gov/10585240/ You may remember the topic of dopamine being tossed about here earlier this summer. Interestingly, to me at least, dopamine also has been studied in wee bitty bee brains able to produce their utopic eusocial societies, paragons of patterns of sustainable specialization and trade. Might smaller brains be consistent with a theory that humans are evolving in a eusocial direction? https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7746283/
I'm generally very suspicious of pop science books. Especially on this subject. I'd have to know more about it.
That looks more linear than exponential to me, just eyeballing it.
But even before looking at the link I didn't expect to see any kind of S-curve or plateau. Wouldn't it be an implausible coincidence if the amount of intelligence humans need to invent agriculture and civilization required millions of years of evolution, but then we hit an intelligence maximum or equilibrium within a dozen millennia of that?
Look at it again. The horizontal scale is logarithmic.
Well, not logarithmic, or fitting that "0" on the axis would have been quite a stretch, but it's certainly very nonlinear. Thank you for pointing that out.
I heard someone in a podcast, I think it was Greg Cochrane, say that many of the things intelligence is good for are public goods (inventions, discoveries, etc.). So, the evolutionary pressure to select for intelligence is not that strong.
"Reproductive Cost"
There is also the literal problem of a woman having to squeeze a bigger skull out of her vagina, which is a constraint.
"Social Theory"
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.
Being a lone smart person has evolutionary drawbacks as well. Think Archimedes being slain by the Roman soldier because he couldn't read the social situation.
So, archimedes had low social intelligence. And, humans can keep growing after birth, so women don't necessarily have to give birth to babies with bigger brains.
If “just grow after birth” was all that was needed we wouldn’t already have these giant brains at birth that are difficult to squeeze out and babies that take forever to grow the rest of their body into those heads compared to most species.
https://socialsci.libretexts.org/Courses/Rio_Hondo/CD_106%3A_Child_Growth_and_Development_(Andrade)/04%3A_Physical_Development_in_Infancy_and_Toddlerhood/4.02%3A_Proportions_of_the_Body
Women( and men) were probably larger due to better nutrition. The world has been heading toward worse and worse malnutrition for the last few centuries due to censorship and other kinds of slow war tactics. Governments don't just attack each other. They also attack their own people. Nowadays, I see media outlets on earth constantly attacking raw milk and saturated fat. Government schools don't talk about the role played by micronutrients such as minerals and vitamins. Most people think macronutrients and ignore micronutrients. Ignorance of micronutrients is apparent among body builders who care more about nutrition than most people. Women who lived on traditional diet including raw milk had wider hips suitable for giving birth to babies. Nowadays, women have narrow hips unsuitable for giving birth, and doctors recommend C section even when women can handle natural birth. Narrow hips result from calcium deficiency caused by lack of calcium, phosphorus, vitamin A, vitamin D, or vitamin K2. Raw milk provides all of them adequately. Pasteurized milk is deficient in vitamins.
Women couldn't have evolved to give birth to smaller babies within a few hundred years. Humanity hasn't had enough time to adapt to this worldwide (malnutrition) propaganda campaigns aimed at reducing population on earth. The same calcium deficiency is also the primary reason for dental cavities.
When you are deficient in those nutrients, your teeth will lose protection from bacteria and foods in your mouth. Fluoride doesn't really protect your teeth, and drinking fluoride through tap water is like drinking sunscreen. You are supposed to coat your skin with sunscreen, not drink it. You can medically coat your teeth with fluoride at a dentist clinic, but that won't protect you from dental cativites. Nutrition and hygiene protect your teeth from dental cavities. Without nutrients, your teeth lose calcium over time. On the other hand, fluoride is a known neurotoxin used to kill mice. More fluoride in tap water results in lower IQ among people.
Humans need more time to adapt to depopulation pressure that manifests in various ways including malnutrition propagandas and fluoridated tap water.
World governments have been obsessed with reducing human population on earth for quite a while. They also push various wars we don't need.
I'm angry with immorality of the ruling class, but it will take a long time time to rectify this if it's even possible to stop them.
Another potential biological cost is size of the cranium at childbirth.
There is also potentially a social cost. Increased "intelligence" (i.e. analytical reasoning ability) presumably had sharply reduced payoffs in the distant ancestral past, because there were fewer ways to put it to productive use. But the drawbacks of an analytical mindset would have been as sharp as ever.
I don't think that intelligence is limited to analytical reasoning ability.
What about the restriction on head size in order that the female can give birth? I understood that was the restriction.
Fair point. That's another biological cost.
Long ago I had an idea for a story I never wrote, involving a species of marsupial aliens. One of the scientific facts they knew was that only marsupials could be intelligent, because of the problem you mention. They observe Earth, are puzzled as to where the intelligent species responsible for skyscrapers and radio broadcasts and such are hiding.
Yes. I have amused myself with the same idea for years.
Humans can grow after birth. So, women don't have to give birth to babies with bigger brains.
But, a bigger head should be accompanied by a bigger body. A bigger body requires more nutrition. More nutritional requirement is bad for survival.
Elephant has a bigger brain and a bigger body, but it is stupider than humans.
Related to "Reproductive cost" but not mentioned: there is an opportunity cost of seeking to mate with smarter partners. The harder it is to find and vet a genius partner (which, in particular, could have a large cost for those lower on the ladder), the more sense it makes to make the choice quicker and have more (non-zero) children with worse partners in the meantime.
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. But that kind of intelligence isn't a primary survival trait; people who have it aren't necessarily good at quick thinking in an emergency, for example. A society needs a healthy supply of people with street smarts (or bush smarts) to support a small number of intellectually smart people who can do specialized mental tasks.
Most people can do abstract thinking, but they just don't want to do it.
I don't want to play chess, but I can learn to play chess well.
Being able to learn algebra, or even calculus, if you have to, is not the same thing as being a mathematician. For that matter, I have my undergraduate degree in mathematics from a fairly rigorous school, but I'm not a mathematician.
In most cases, if you haven't been damaged with bad foods or bad chemicals or bad air, you can become a mathematician as long as you actually want to become one.
Some people are too stupid to become a mathematician or become rich because their brains were chemically or genetically damaged by something. People don't just become stupid for no reason.
Everything has a cause. In the past, people used to believe lung cancer had no cause, but they now know smoking is a major cause of lung cancer. Air pollution is a major cause of lung cancer.
If you drink too much fluoride in tap water, your IQ can go too low to become a mathematician. Drink clean water. Fluoride is a potent neurotoxin used to kill mice.
However, I don't recommend becoming a mathematician especially if you want to become rich. I want to be rich.
Obvious point that you don't seem to address.
You don't need to be among the smartest human beings. You need to be among the smartest people in your village/tribe.
Relative differences in intelligence are magnified when you bring together in a single society/community humans whose ancestors were separated for thousands of years.
If being the smartest person in your village results in producing more children, intelligence in your village is being selected for and will increase.
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.
Nerds & academics are social misfits.
As for why, the answer probably lies within biology, psychology, neurology.
The genes/neurons/etc. that collectively that make someone more intelligent usually also make them socially disabled & the genes/neurons/etc. that collectively make someone more cool/socially skilled, on average, don't correlate to intelligence.
(I avoid the term "wiring" because I don't know anyone who was born with wires in his head.)
If you want the data to back it up, ask Emily Kierkegaard.
I said nothing about academic intelligence. Or nerds.
Fair point. I just was using examples of people with high measurable intelligence with low social awareness.
The more interesting question is why is there a general negative correlation between intelligence and intuitive social awareness.
That's a common belief. Do you know of statistical evidence?
https://www.sciencedirect.com/science/article/abs/pii/S1090513805000619
Table 3, model 8
I assume you are taking frequency of sex as a proxy for social awareness. But I find:
"This analysis suggests that intelligence has little effect on frequency of sex, and this does not differ for men and women."
In model 8 they are, I think, controlling for income. So I read the result as "Rich men who get no words correct have more sex than rich men who get words correct." Am I correct?
A recent article that just popped up for me, along the “race car” line:
https://www.sciencealert.com/the-larger-brains-of-humans-come-with-a-tragic-cost-study-finds
Biology is messy, and members of a species rarely all hit the same target on a metric, unless the quality is under immense selective pressure (e.g., fertility, ability to learn human language, lactose tolerance in infancy). Expecting everyone to come out the same height or IQ is a non-starter of a premise.
I don't buy #2, or at least I would buy it's inverse "why are we all not morons" as in retarded people tend to reproduce less but not the opposite. 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.
And I think that holds historically as well and I'd even go as far to say smart man gets his head bashed with a rock trying to negotiate while dumb man rapes and pillages his village at the behest of his average intelligent war chief. The reproductive advantage is simply not to overly ponder the future, take and breed who you want now, die young but your children will inherit the earth and maybe some of them might even be smarter on average since you raped the nunnery and nobility too. Smart guys are killed in war, the average low IQ winner or even lower IQ civilian who couldn't even make it into a press gang repopulates the losers lands.
You are generalizing from a society so rich that even poor people can afford to rear ten kids to adulthood. That is not the environment our species evolved in.
I would add a few options that overlap some with yours:
Good enough is good enough: the returns for intelligence are diminishing, and often being pretty smart and having access to allies who are very smart is just as good as being very smart yourself. Selection effects for individual intelligence are thus not terribly strong, so wider variety is workable.
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.
Very smart people often find mental pursuits more interesting than physical: People who put mating and other status games at a lower priority relative to curiosity and mental pursuits are going to do less well.
So all together, if smart enough to get by is the common feature, the norm that society conforms to, very smart people are going to be selected against somewhat if they do not conform or successfully compete in the status and mating games of their group due to conflicting interests. Being less intelligent is not necessarily selected against if there are smart people you can ally with to take advantage of their cleverness through advice or trade, etc. Excess intelligence that alienates from others in the group tends to be a big problem, especially in the face of low returns on intelligence compared to today.
I would also throw in that intelligence seems to have very sharply diminishing returns when social rank is relatively fixed. A hunter gatherer tribe member might not have strong returns to intelligence, but a medieval serf might have somewhat negative returns. The serf doesn't get to plan improvements to his land, or decide different ways to plant, or get to run off and become a merchant or architect; in fact any impulse to do so might get him in a lot of trouble or dead. As a result, intelligence above a certain level is probably actively selected against as someone who finds a life of farming excruciatingly boring is likely to get himself killed. A certain lack of imagination and willingness to just accept a bad situation is probably good for living long enough to reproduce.
I think you are mistaken about the medieval serf. He does decide how to run his farm, and you may be underestimating how much intelligence is involved in doing so. At least after the 14th c. running off to do something else was an option — "City air makes free."
Fair point, I was over generalizing a good bit. I think it is true that he doesn't get to plan improvements to his land, because it is not his land to improve and so is limited to what the landowner will do or allow. I am also fairly certain he couldn't plan to say raise pigs suddenly if he was supposed to be growing flax and wheat. Depending on where one was and the legal framework of the time, however, there are probably big swings in autonomy and the returns to decision making and thought, you are correct.
While I agree that a level of intelligence is needed for farming it is worth keeping in mind that for much of the time it is pretty dull. After the planting there is not a lot to do other than keep birds and animals from nibbling the crop and weeding, which is why kids and wives were usually left to it while the men went off to raid and fight during the summer months. Harvesting is long, dull work. Planting is long, dull work. Some people might find it pleasant, but like the people who find cost accounting pleasant they are no doubt a small minority. Further, when most of your crop goes to someone else there isn't much incentive to apply your brain hard to the problem of getting more grown, either. I suspect there is a reason that for centuries the pattern was the smart children left the small farm for the city. It just wasn't the sort of environment that a very smart person could find interesting for very long, and the percentage of people who find that sort of thing interesting or pleasant is a small percentage of the population compared to the percentage of the population who did it for a living.
Related to this, and the laws in a time and place aspect, I recall reading that 18th c. Russian peasants (near slaves in places) were considered to be remarkably dull by western (British and French) soldiers that encountered them in the Crimean War, as compared to British and French peasants. No doubt there is a lot of jingoism there, but it tracks with the notion that harsh regimes with near zero social mobility tend to breed people selected for putting up with bad stuff and a certain lack of imagination for expecting better.
"Further, when most of your crop goes to someone else"
I think you have a somewhat distorted picture of the medieval system. Checking online for feudal dues, I find "in most cases, it was up to 30% of the harvest." Typically the peasant owned his own land but owed feudal dues on it, rent set by custom not free bargaining, might also owe some labor on the lord's land.
Again, differences in time, place and custom, as well as the distinction between serfs and peasants, are going to be relevant.
I do note that many serfs had the obligation to work 1/3 or 1/2 the days on their manor's fields instead of their own. If that is in addition to the up to 30% rate on gross production, that is a very steep tax rate. Also don't forget the church gets its cut (10%) along with anything else. But I can go with "much of your crop" instead of "most".
What tax rate do you think is sufficient to push people away from working harder to invest in more output vs engaging in more leisure?
And what do you believe the expected (or observed) rate of return on investment in improved farming practices to be to the average medieval serf?
How much does an extra point of IQ change that?
Those seem to be the key questions.
Serfs also only kind of owned their land, again with variances for time and place, with the landlord being the owner and the serfs having rights to live and work the land. How much any of that would track with our modern concepts of ownership is vague(there are arguments about whether US citizens own land vs the US government owning the land and we merely own the rights to use it for somethings), but it wasn't clearly fully owned by the serf.
Getting all this back to the point of its effects on IQ in an evolutionary sense, we would need to ask what a substantially higher IQ would do to benefit a serf. (Remembering that for quite a while that was a very large proportion of the population.) Using high IQ to figure out farming is non-trivial; the green revolution took forever because agriculture is complicated above a certain level, has very long cycle times on feed back(especially in colder climates), and if you are close to starvation screwing up experiments is really expensive. So people tend to apply a lot of shared knowledge and inherited wisdom (which doesn't require much IQ for the individual, just the existence of some smart people). If you are high IQ you can't stand on the shoulders of giants by doing research because it isn't available, you can only stand on the same shoulders as everyone else. You can do your own experiments and pay lots of attention, and that probably helps a bit, but it has long cycle times (one harvest per year) and many outside variables you can't control. If you increase crop yield by a crazy high 10% you get to keep 7%, and hopefully none of those outside factors diminish the output such that you hardly notice that you had a big increase. (E.g. your novel irrigation helps a lot, but plant disease and hungry birds are worse this year and your crop only improves by a tiny bit, making it hard to tell whether it worked.)
Plus the higher IQ person has to avoid the common higher IQ mistake of "This is totally going to work, I am going all in!... whoops" and killing themselves. Thinking you are smarter than everyone else and therefore aren't wrong is a common trap for people who are actually smarter than everyone else.
Throwing in another "in addition" category, if wealth isn't the only source of reproductive success, there are other avenues that IQ might not be selected for after a certain level. If people care about status, not just "the wealthiest serf" sort of status matters, but also "the biggest and strongest" or "the best at shooting a bow" or whatever. Not all of that is going to be highly correlated with intellect, and much of it might be negatively correlated. If I have to choose between between potentially increasing crop output through hard mental work or screwing around with my friends at playing whatever local game is high status, for instance, a smarter person might focus on crop output and be a little richer, while a dumber person might say "eh, good enough is good enough" and focus instead on being the best footballer. It is not clear ex ante that one will be more reproductively successful.
Lots of evidence about the brain size and intelligence correlation and the causal effect of the former on the latter. https://www.emilkirkegaard.com/p/brain-size-and-intelligence-2022
The comments are fun. But don't forget that high intelligence is also frequently distractable. And high intelligence doesn't win all 'contests' that might lead to reproductive success.
I personally know a very ugly and not very smart woman who has 6 children. She's a sweet person, but . . .
The 6 children have at least 3 different fathers and in all likelihood all would test at or just below 100 IQ. As long as such women can find men willing to mate with them Evolution is not at all 'selecting' for intelligence. And as my sainted grandmother used to say, "Men are dogs, and some of them would (mate with) a knothole in a wooden fence."
Evolution rewards whatever makes/allows you end up with grandchildren, preferably many grandchildren.
Also, in mt experience (I have no data at all), many high IQ males don't seem especially interested in sex at all. The highest IQ women I know at least seem to seek high IQ, successful (in one field or another) males, but may not have children.
We are in a very rich society in which even a not very successful woman can afford to bring lots of children to adulthood, also a society with reliable contraception to let people sacrifice the genes' objective to their own. Neither was true for most of our species history. So your observations, while they may be true, are not very informative for explaining the results of human evolution.
Sure, but prior to us becoming rich we also were still basically small groups for millennia where having living children was a group goal, so the societal pressure was in line with maximizing the number of offspring from all women, roughly speaking. Another set of hands, even at age 4 to 5 was a benefit.
Also, it's likely, I think, that IQ in general was held down due to lack of quality nutrition, and disease, variables which persisted well into the 20th century in the US. Even a really good hunter married to a really good gather might still not have necessarily always been able to provide good nutrition.
High IQ is not always as important as other qualities, so the evolutionary pressure is probably not as great as one might imagine as on the single variables. Nature's motto seems to be, "If it works, it works, and anthing that produces offspring must be working."
For if everyone were a genius, there would be no genius; it is a relative concept, like any other concept. Take the term "human"; there must be non-humans for such a term to have any use or meaning. So to speak, difference is the a priori of any concept; if there is a concept, it is already decided.
I would also add: fluoride, glyphosate, aspartame, glutamates, BPA/BPS, Atrazine, chlorine, lead, GMOs, ethyl alcohol, whole language, and common core!