Dumb Farmers

Apparently the foraging life is more mentally demanding than is the farming life.  Brain size rose during the forager era, but fell during the farming era. During the industry era brain size is rising again, yet another way we are returning to forager ways with increasing wealth.

Combined with social brain theory, that our brains are big to deal with complex social worlds, suggests farmer social worlds are less complex.  Perhaps this is because stronger town social norms better discourage hypocritical norm evasion.

The data:

Over the past 20,000 years, the average volume of the human male brain has decreased from 1,500 cubic centimeters to 1,350 cc, losing a chunk the size of a tennis ball. The female brain has shrunk by about the same proportion. … “This happened in China, Europe, Africa—everywhere we look.” … “I think the best explanation for the decline in our brain size is the idiocracy theory.”

When population numbers were low, as was the case for most of our evolution, the cranium kept getting bigger. But as population went from sparse to dense in a given area, cranial size declined, highlighted by a sudden 3 to 4 percent drop in EQ starting around 15,000 to 10,000 years ago. “We saw that trend in Europe, China, Africa, Malaysia—everywhere we looked.” … Skulls of Europeans dating from the Bronze Age, 4,000 years ago, to medieval times. Over that period the land became even more densely packed, … [and] the brain shrank more quickly than did overall body size, causing EQ values to fall. … in fact, [this] pattern … is even more pronounced. …

What may have caused the trend … is selection against aggression. In essence, we domesticated ourselves, … Some 30 animals have been domesticated … and in the process every one of them has lost brain volume—typically a 10 to 15 percent reduction compared with their wild progenitors. …

“Wild types and domesticates think differently.” … Wolves, with their larger brains, are more prone to flashes of insight, allowing them to solve problems on their own; dogs, with smaller brains, excel at using humans to help them. “Wolves seem to be a little bit more persistent than dogs in solving simple problems like how to open a box or navigate a detour,” Hare says. “Wolves persevere when dogs readily give up.” On the flip side, dogs leave wolves in the dust when it comes to tracking the gaze and gestures of their masters. …

He suspects that [bonobos] are domesticated chimps. … “Bonobos look and behave like juvenile chimps … They are gracile. They never show lethal aggression and do not kill each other. They also have brains that are 20 percent smaller than those of chimps.” Hare thinks bonobos became domesticated by occupying an ecological niche that favored selection for less aggressive tendencies. …

When … Richard Jantz … measured the craniums of Americans of European and African descent from colonial times up to the late 20th century, he found that brain volume was once again moving upward. (more)

Added 7p: Many suggest we explain this via lower farmer nutrition.  But this would much better explain a sudden fall than a steady gradual decline.

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  • eigenman

    How much of the change in brain size could be attributed to nutrition do you think? I bet a lot.

  • http://whyiamnot.wordpess.com Salem

    Brain size =/= intelligence.

    Test your theory: Are modern hunter-gatherers more intelligent than modern peasant farmers?

    • ty thompson

      Yes, they are. They had to keep track of all the predators of the day, defenses, escape and evasion tactics. They had to remember all local fauna, what’s edible, what’s poison, what they are more likely to catch prey near. Remembering countless prey animals, their habits, behaviors, capture techniques, their relation to other predators and prey animals. How to deal with competing clans, their habits, ranges, possibly partial cooperation. Studies have shown that indigenous populations more readily grasp geometry and similar spatially oriented sciences than people from developed countries.
      Along those lines, people with no economic training score better in economics than those with PHDs. Go beyond a certain extent in education and you get too much into the theoretical and you can hand pick anything that sounds good in theory to support your views or biases. Indigenous people deal with reality every day and very little social conditioning. So when you relate to them a theory, they are more likely to call BS on something that isn’t workable or logical. They are more accurate on many topics than the educated from developed countries.

  • http://entitledtoanopinion.wordpress.com TGGP

    Funny, I heard that Australian Aborigines (who retained hunter-gatherer ways for much longer) had smaller brains and thicker skulls (the better to withstand whacks to the head, my dear).

    Richard Wrangham has a theory in “Demonic Males” on what ecological niche resulted in bonobos. If you’ve read his second book, you may not be surprised that it involves food. Incidentally, I believe they also have larger group sizes compared to the common chimpanzee.

    • Broggly

      That sounds just like the old “Pith Helmet” myth, that Europeans had to wear pith helmets when in the tropics because their big brains would overheat in the sun, while small brained natives were protected by their thick skulls.

    • ty thompson

      Australian Aborigines are not as subject to predation as other indigenous cultures nor as diverse an ecosphere.

  • Jess Riedel

    Is there a good summary for how well skull volume predicts intelligence? Obviously, absolute skull size isn’t that great (elephants and whales are dumber than chimps), but is the skull-volume/body-weight ratio much better? I’m under the impression that within a human population, relative brain size correlates very poorly with intelligence (be it EQ, IQ, or some other type). If it’s not a good proxy within one species at one time, why would we believe it works across species and times, given that that different environments will naturally select for different skull shapes, temperature regulation, hormone balances, etc.—even when those environments demand roughly the same intelligence.

    Also, how are they possibly measuring EQ 10k years ago?

    Of course, as long as we consider just skull volume as such, then this is still evidence that humans are becoming more forager like; it just may not be good evidence on its own that they are becoming behaviorally or mentally more forager like.

    • Khoth

      Also, how are they possibly measuring EQ 10k years ago?
      EQ in this context is Encephalization Quotient, a way of expressing brain size.

  • http://www.bayesianinvestor.com Peter McCluskey

    Temple Grandin, in Animals in Translation, says that in humans it was the midbrain and the olfactory bulbs that shrank, but in other animals undergoing domestication the forebrain and corpus callosum shrank (no references provided). She interprets that as a division of labor in which dogs took over some sensory functions previously performed by the human mind (smelling prey?). The timing seems right for this – there’s clear evidence that dogs were domesticated at least 12000 years ago, and some reason to suspect it happened at least 30000 years ago.

  • donK

    Steven Jay Gould’s “The Mismeasure of Man” discussed at length the problem of correlating cranial volume and intelligence. I would expect childhood and adolescent malnutrition as well as disease to correlate with population density in preindustrialized societies. As those constraints are removed the population will better represents its genetic potential. I don’t dispute the the self domestication theory, but contend that the resent increase in cranial volume is more likely due to nutrition and health care than a fundamental genetic shift, especially when better nutrition and disease prevention reverse the downward trend.

    • http://entitledtoanopinion.wordpress.com TGGP

      Haven’t read Gould’s book, but I heard he relied on Franz Boas regarding skulls. If you don’t mind reading racist blogs, some coverage of the anthropologist R. L. Jantz’ revisiting of Boas’ work on skulls here.

  • JAMayes

    As others note, brain volume and intelligence aren’t necessarily the same. But even if they were, your conclusion about life being more “mentally demanding” for foragers wouldn’t follow. Particularly given how short, relatively speaking, the farmer period was, I’m very skeptical that any observable differences were the result of natural selection breeding out “excess” intelligence rather than the result of changes in nutrition, excercise amounts, exposure to diseases or something else that arose along with farmer culture.

  • Abelard Lindsey

    Two explanations immediately jump out at you:

    The first is better nutrition. It is well-known to anthropologists that hunter-gathers had far superior diets than subsistence farmers. They lived nearly as long as modern people (mid 60’s) and kept most of their teeth through-out life. Agriculture was a giant step down for most humans.

    The second explanation is simply that brains, like muscle, atrophy when not used often. It is becoming well-known that people who come from a community of believers of doctrinal religion (e.g. Islam) have mean IQ substantial below the mean of those from industrial secular societies (West, East Asia). Usually this differential is ascribed to inbreeding (cousin marriage is common in Islamic societies). But it may also be attributable to the fact that Islam is, by far, the most proscriptive of all of the world’s major religions. They have fatwas for literally every possibly human activity down to something as insignificant as how to brush your teeth. The more proscriptive a religion is, the less you have to use your brains for thinking.

    • http://entitledtoanopinion.wordpress.com TGGP

      I find the religion theory pretty doubtful. Are there any long-standing borders of Islam a la East vs West Germany or North vs South Korea than can serve as a “natural experiment”?

      • Abelard Lindsey

        Possible. However, people in both societies suffered from sub-optimal nutrition compared to their Western (or Southern) counterparts. So, parsing out which is due to sub-optimal nutrition as opposed to simply not using ones’ mind is difficult in these two cases.

    • Konvkistador

      Have you heard of Orthodox Judaism?

      • Abelard Lindsey

        Yeah, the ultra orthodox are just as psychotic as the fundamentalist Muslims. Any form of religious fundamentalism is psychotic.

      • http://entitledtoanopinion.wordpress.com TGGP

        They may be “psychotic”, but they are not known for low IQs. Robert Aumann is orthodox, and Eliezer Yudkowsky at least was raised that way. He looks like he has a pretty big noggin to me.

      • Abelard Lindsey

        TGGP,

        I don’t care what you think about my attitude towards religion. To be honest, I have friends or at least know people of probably every religion on the planet (Buddhist, Hindu, Sikh, Muslim, most flavors of Christianity). I get along well with these people as they do with me. For these people, religion is a part of their self and cultural identity. It is a personal belief system for them. I respect these people and their worldviews.

        I have no problem with those who believe in religion as a personal worldview or philosophy.

        I have absolutely no patience or tolerance for those who make a political ideology out of it. Religion has no place in politics, period. Those who try to inject religion into political discourse utterly disgust me.

        This is all I am going to say about religion.

      • http://entitledtoanopinion.wordpress.com TGGP

        Nothing I have said questioned or commented on your attitude toward religion broadly, just the connection between it (or its proscriptiveness) and brain size. That was the initial subject of Robin’s post and your comment

      • Abelard Lindsey

        Religious belief is a form of mental illness, plain and simple. Plenty of intelligent people are mentally ill.

  • http://akinokure.blogspot.com agnostic

    Lots of others have already said it, but I’ll reiterate to emphasize and add another example. If shrinking brains means lower intelligence, that’s due to poorer nutrition and greater infectious disease burden.

    It has nothing to do with densely packed areas per se, only those that were agricultural rather than industrial. Industrial people leave very close together, but they have much better nutrition, as of recently they have antibiotics, and they have a central state to check violence.

    This also shows that domestication of aggression has nothing to do with it, since that would imply an industrial-era return toward hunter-gatherer levels of violence. In reality, homicide rates have fallen by two orders of magnitude from circa 1600 to 2000.

    The other pattern that looks just like brain size is height. Hunter-gatherers were tall, farmers were stubby, and with industrialization they recovered their heights during the 20th C. To capture both height and brain size, we only need to point to changes in the diet and infectious disease burden. Social complexity, domestication of aggression, etc., doesn’t capture the similar changes in height.

  • http://akinokure.blogspot.com agnostic

    Homicide rates in Western Europe, that is.

  • Matt

    Except this happened to foragers and farmers alike. There’s no pattern of social complexity increase or agricultural effort correlating with brain size reduction. Bushmen and Australian Abos have lost as much, or more, as Chinese, and have lower total sizes.

    That’s not a “farming is dumbening” picture. The only counterveiling confound would be if farming populations were expanding into foraging populations and gradually supplanting or replacing them. But since this happens where we can be confident this isn’t an issue (unless Aborigines and Bushmen and New World HGs all have substantial, total, gene flow from agricultural pops), this is probably wrong.

    http://www.youtube.com/watch?v=8i238fyDjVg – Video talking about the trends.
    http://blogs.discovermagazine.com/gnxp/2010/12/slouching-toward-idiocracy/ – Razib Khan’s take.

    • http://hanson.gmu.edu Robin Hanson

      Foragers and farmers over the last few thousand years have high levels of interbreeding. We are one species, not two, and evolve together.

      • Matt

        We are one species and of course foragers have exchanged genetically with farmers, however we would be one species regardless of whether these hunter gatherers had had genetic exchanges with farming communities or not.

        In any case I believe the weight of evidence suggests that the cranial reduction in foragers is largely endogenous and not the result of gene flow from farmers. Certainly, the cranial size reduction trend in foragers predates the “last few thousand years”.

  • http://www.gwern.net/ gwern

    Offhand, I think there are any number of biases that might give this result while not reflecting any real changes.

    For example, perhaps there is a selection bias. Large skull correlates with good health & nutrition, I think. Perhaps foraging life involves large variations (feast or famine) such that the weaker (and smaller-skulled) die disproportionately. When we measure adult skulls, we find they average out to be large, while the farmer skulls have a lot of surviving small adult skulls dragging down their average.

    If aggression were the whole story, an increase in European skull sizes would be surprising, given the claims by the likes of Pinker that violence has declined dramatically over the past few centuries/millennia.

  • Dave

    Does urbanization turn us into big brained forgers? Observations of brain size seem to support this.What does not correlate is body size. From forensic anthropologists I hear that the human body is rapidly becoming more gracile,to the extent they have trouble telling a man from a woman,if only fragments of the skeleton are found. So urbanized people are turning into wimps,not foragers. So if they are smarter but with sissy bodies,might not your theory be called “The Revenge of the Nerds?”

    Or alternatively,there are regular farmers,and there lazy farmers. I know some regular farmers. According to these regular small brained farmers there are some even stupider farmers who do things like letting trees grow over their fields.They are too lazy to cut them back. The lazy farmers,also known as rednecks, mostly rely on welfare and their kids don’t do well in school.They do very well in reproduction.

    So,I would challenge the idea that modern “forager” behavior connotes smartness. Perhaps I don’t understand the terminology. Or perhaps there should be an additional category that combines the features of both categories. This category is the one that really thrives today. Call them “Spongers” The category would have the following features:

    TYPE *C* Spongers eat a lot of French fries,and get little exercise. They tend to stay in the same place except when released from jail when they move often to a new communities. They work few hours. They talk openly about sex, are sexually promiscuous. They have a lot of kids, whom they are reluctant to discipline or constrain. They spend little time with their kids. Type C- folks care a lot for material possessions, but have little. They deal with conflict with violence or threats of violence. When they work they hold tedious and less healthy jobs. They are often unfaithful to their spouse. They have little in common with farmers but considerably more resemblance to foragers.

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  • Amanda

    How specialized was the division of labor in a forager vs a farmer society? I would imagine foragers would have to be adept at more varied tasks, and possibly have to handle short-term problem solving more than a member of a farmer society. In the farmer society, I would imagine that specialization of labor caused the individual to be responsible for less tasks, the “whole brain package” became less attractive from an evolutionary standpoint, so brains that were smaller, but possibly more specialized were the result.

    However, that explanation does nothing to explain the last paragraph, where its stated that brain volume has begun moving upwards.

  • vaniver

    I would be far more interested in skull (and thus brain) *shape* than size. If we’re losing parietal volume to get frontal volume, we’re getting smarter by our metrics.

    (There are other reasons to suggest skull size and intelligence wouldn’t move in the same direction, but I assume you’re familiar with those.)

    • Matt

      If you watch the video I posted, you will indeed see that change is driven by a disproportionate reduction in length, although secondary sources (http://dienekes.blogspot.com/2006/08/trends-in-cranial-capacity-and-shape.html) not in that video indicate that this may have happened in Eurasia only (in Africa, volumes decrease without brachycephalization – possibly climate matters here).

      The change in brain shape from archaic humans to modern humans was driven by parietal expansion, so if there was infact a loss in parietal volume relative to frontal volume (rather than relative occipital loss, for example), I would not be so confident in whether we would be getting smarter by our metrics.

      “In humans, the frontal lobes contribute heavily to social behavior and the planning of future actions”

      “Technological, abstract and computational thinking seems to arise in the parietal lobe”

  • http://daedalus2u.blogspot.com/ daedalus2u

    A very large driving force for brain shrinkage may be cephalopelvic disproportion. Without medical c-section, a few percent of women die in child birth because their baby’s brain is too large.

    Optimization of brain function, so that a smaller brain can do the same as a larger brain would be a fabulously successful adaptation.

    Of course if thinking is of no value (or negative value), then a small brain would be better.

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  • Miguel Madeira

    It is general knowledge that predators have bigger brains than herbivores, because huntig moving animals requires more cognitive effort that “hunting” fixated grass; than, it is logical that foragers should have bigger brains than farmers.

    “Combined with social brain theory, that our brains are big to deal with complex “ocial worlds, suggests farmer social worlds are less complex. Perhaps this is because stronger town social norms better discourage hypocritical norm evasion.”

    Or the social brain theory is simply wrong?

  • http://www.isteve.blogspot.com Steve Sailer

    Where’s the evidence that forager bands who survived into the 20th Century are terribly intelligent? We have lots of ethnographic data on, say, Australian Aborigines or Bushmen. Most of it is depressing about their ability to adjust to the modern world. In particular, abstract thinking is uncommon among foragers.

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  • http://daedalus2u.blogspot.com/ daedalus2u

    There is a gigantic driving force for smaller brains, the 1% or so maternal death that occurs in childbirth per pregnancy in the absence of medical C-section due to cephalopelvic disproportion.

    I think what is being selected for is greater specialization in brain function, programmed in utero. A tribe needs experts in many different fields, not everyone with equal abilities in all fields. I think that maternal cephalopelvic disproportion has driven greater specialization of the human brain and that specialization has to occur in utero, when the major structures of the brain are being formed.

    If this is correct, it explains why no one can find any “genes for intelligence”. There aren’t any. What is important for a successful tribe with successful genes is that it have multiple experts. The tribe with an expert tool maker, an expert rope weaver, an expert wood carver, an expert tracker, an expert wild-animal domesticator, where those experts can pool their expertise and teach the other non-experts how to make and use each of their expert-level products will do much better than a tribe where all its members have the same level of expertise and has no experts.

    The “successful” genes that make the tribe “successful” and so are shared by the members of the tribe are the genes that create diversity in abilities. That diversity can’t be genetic because it would then require genetic diversity to achieve phenotype diversity and a tribe consists mostly of related individuals. The successful genes must be those that create cognitive diversity without genetic diversity. They must get their “diversity” from somewhere, they must get it from coupling to the environment in utero at the level of noise via stochastic resonance and not from genetics.

    This hypothesis explains the inability to find genes for intelligence, explains the Flynn effect, it explains why animal models are inappropriate (they didn’t have hundreds of millennia of evolution driving diversity in cognitive abilities in limited brain sizes).