Humans are domesticating themselves with smaller brains as a result

Marginal Revolution posted the following excerpt from Jeremy Taylor's book titled Not a Chimp: The Hunt to Find the Genes that Make Us Human.
200911201140 I think we have to start thinking about the idea that humans in the last 30, 40, or 50,000 years have been domesticating ourselves.  If we're following the bonobo or dog pattern, we're moving toward a form of ourselves with more and more juvenile behavior.  And the amazing thing once you start thinking in those terms is that you realize that we're still moving fast.  I think that current evidence is that we're in the middle of an evolutionary event in which tooth size is falling, jaw size is falling, brain size is falling, and it's quite reasonable to imagine that we're continuing to tame ourselves.  The way it's happening is the way it's probably happened since we became permanently settled in villages, 20 or 30,000 years ago, or before.

Jeremy Taylor's brain is not yet too small to notice that our brains are becoming smaller



  1. so it sounds to me like you’re saying that we probably might be getting dumber as a result of something that may or may not have started 20 or 30 thousand years ago. Excellent work.

  2. I don’t know of any evidence of shrinking human brainsizes in this timeframe. I’d love to see a reference. The quote itself seems a bit tentative: “I think that current evidence is..” He ‘thinks’ so?

    There is evidence that humans have evolved materially since the dawn of agriculture. Selective pressure on genes for lactose digestion is the common example.


  3. By the time this matters the robots will already be in charge. Or we’ll have robot brains attached doing the heavy lifting. Either way.

  4. Jared Diamond of Guns, Germs, and Steel made a similar point: he spent many years in Papua New Guinea with the indigenous people, and found them to be a lot more intelligent than the average Westerner, quickly grasping ideas that his university students had hard times with. He speculated that the reason is that in a hunter-gatherer society in the jungle, stupidity gets you killed, while if you live in a large city, having a poor immune system gets you killed. And one of the main points of the book is that it was mainly the triumph of Western immune systems that led to the quick defeat of indigenous peoples by Europeans.

  5. I think he’s giving too much credit to the humans. I prefer the hypothesis that wolves domesticated Killer Apes to act as scouts for the pack. Except for Romulus and Remus striking out on their own it’s been all downhill since then.

  6. Either he’s saying that people with smaller brains, teeth and jaws are more successful breeders, or he doesn’t understand evolution.

    Traits don’t shrink away from disuse.

    1. Either he’s saying that people with smaller brains, teeth and jaws are more successful breeders, or he doesn’t understand evolution.

      In an environment where you do not need a large brain, large teeth, or large jaw, people with smaller brains, teeth, and jaws WILL be more successful.

      It takes a lot of metabolic expense to grow a brain big, and its an ongoing expense to feed a big brain. More bones and teeth (hard tissues) is again, more metabolic expense in the growth phase. Size of any kind is expensive, but especially of that big hungry brain on top of your shoulders.

      Eyes are another area that take up a lot of metabolic energy.

      If the feeding advantage that a big brain gives you is not enough to offset the metabolic cost of a big brain, then the guy with a baseball for a head will thrive on calories that the guy with a soccer ball for a head will merely survive on.

      Better nutrition = better health = more fertile = more attractive to mates and more successful at actually producing offspring once you mate, and your offspring start at a significant physical advantage.

      1. ith a baseball for a head will thrive on calories that the guy with a soccer ball for a head will merely survive on.

        I know you weren’t being literal with the baseball/soccer ball comparison, but there’s not enough head-size variation and calorie scarcity in our population to make that a positively selected trait.

      2. Re: Smaller features conserves energy, which makes you healthier and more likely to mate: Doesn’t this assume a limited food supply? Most Westerner’s don’t need to conserve energy — in fact, we take in more than we need and end up gaining weight. I would argue that our diet has more effect on our nutrition than the size of or features.

        Remember, evolution is based on the concept that the strong survive. Those who survive long enough to have offspring will have their genes carried on. The earlier and more often they mate, the more their genes influence the gene pool.

        I think it’s fair to say that, if you want a mate, you can find one. What men find attractive in women has little to do with their ability to bear children and what women find attractive in men rarely has anything to do with their ability to provide for their family (unless they are attracted to money).

        I’m inclined to agree with Idiocracy: the determining factor of procreation (and therefore evolution) is intelligence, though I would add poverty as another main factor. Those with lower intelligence and those living in poverty are likely to reproduce earlier and more often.

        The only other thing that affects our survivability in a meaningful way is our health. Those who are overweight, drink, smoke, or otherwise are less healthy won’t live as long. That said, they still live plenty long enough to procreate, so once again evolution shouldn’t be affected.

  7. Actually, getting smarter and more adaptable through evolution has been a function of keeping juvenile features well into adulthood. It’s called neoteny. Youth is a time of change and adaptation. Then at some point, most animals leave the juvenile period, play the hand they are dealt and find out if they get to reproduce or not. Humans are different because we stay adaptable throughout life. We keep learning and playing. We pass on our genes in part by helping our grandchildren. Becoming more juvenile as a species has been, and will continue to be, our salvation.

  8. This of course requires there to be enough variability in the population that smaller brained, jawed, and toothed individuals are produced to compete with their mellon-headed cousins (And win).

    But humans seem to have the physical variability thing down to an art – another trait we share with domesticated species.

  9. Way off track. Recall watching a fascinating bit on some science show-apologies for not having specific references, anyways, in the show, a woman talks about how our brains are getting bigger-she shows skulls from the 12 to 1300’s, and remarks that simple measurement indicates an increase of 13 percent, in forehead size. This is where the frontal lobes are, of course, which are where higher order brain function occurs. Plus, he’s mistaking an acculterated phenomenom. Humans in urban areas don’t have to think quick on their feet-however, personal experience has demonstrated that smarts, intelligence, and such, can be awakened, or accelerated, fairly quickly. A note on skull measurements: the physical measurements are there, the evidence is in, the science ongoing. Add to that, a fairly rapid current change in hemisphere connectivity and other internal changes, leads one to suspect that we are entering a state of change that isn’t externally obvious. all leading to smarter humans.

  10. In junior high my sister’s grade all measured the circumferences of their heads in science class. I’m not sure why they did this, but I do remember that the kids in the advanced class had smaller heads, on average, than the rest of the student population. Probably not statistically significant, but kinda funny.

    As for whether our brains are shrinking, I’ve never heard this assertion before and would like to see references.

    Also, I’d like to point out that brain size as a lone measurement is meaningless. If you think otherwise, I urge you to visit your local zoo and cultivate an inferiority complex near the elephant pen.

  11. When is it okay to say there’s a connection between physiological features (like brain size) and intelligence? When it is not okay? Comment #6 from Joe was allowed, claiming that Jared Diamond claimed indigenous people of Papua New Guinea are “a lot more intelligent than the average Westerner.” Would it be okay to say the average Westerner is a lot more intelligent than indigenous people of Papua New Guinea? Not true or false, but allowed to be published at boingboing at all?

    Either there is or isn’t a connection between physiological features and intelligence, no matter the uncomfortable implications of that fact (or falsehood).

  12. I’m relatively certain that I heard somewhere that brain-size and intelligence are not really related. It’s actually the compactness of the brain that marks genius. (Though I have no idea which causes which). So all in all, if living longer and in comfort means smaller teeth, jaws and brains, I’m totally fine with that.

  13. Meh. This has been discussed in academic circles for decades. The problem is that nobody bothers to read what people used to write, especially if its in the “soft” sciences or philosophical.

    In particular this is the point why nurture vs nature is an ill defined debate: nurture is part of our nature. Claude Levi-Strauss who just died wrote this. I’ve read the statement that humans domesticated themselves in sociological and antrophological texts far back (though google doesn’t lead me quickly to a definite origin).

    This is like exclaiming excitedly that apparently you can now send mail without using paper! Just through finely adjusted electric currents! It’s called e-mail!

    Yet somehow these old, well studied philosophical ideas can always be passed of as surprising amazing insights by some new author. This is failing basic science literacy! The degree to which the humanities progress in finding ways to think about and critizise our way of understanding the world is unknown among otherwise well read, intelligent people is frightening.

    1. And it is still being discussed, just there.

      A lot of people who might be interested were small children decades ago when YOU apparently got wind of it.

      Are you against the refinement of theories or something?

      Can you manage to sit through a remake of a movie you saw the original of? Can you enjoy it? Can you let me?

      1. “A lot of people who might be interested were small children decades ago when YOU apparently got wind of it.”

        I was not born when those books were written, I just don’t make the assumption that we are the first generation who came up with interesting ideas. In fact they have been refined tremendously already and my complaint is exactly that rather than refining them further our ignorance of philosophy, etc, means we’re just going in loops.

        I’m by no means an expert on this stuff, but I know enough to be aware of my ignorance and the complexities involved.

  14. I don’t understand, and I don’t have time to figure it out. I have ten litters of screaming retarded children to slop, and half of them are already pregnant with my grandkids.

  15. 17’s remark reminds me that indeed, about the basics of neurology-brain size compared to intelligence, for instance, we effectively know very, very little. Slime mold, without any neurons at all, has demonstrated the ability to tell time, and predict. Crows and elephants have demonstrated self-awareness. What we have are some working models-indicators, and educated guesses, for the most part. These would be frontal lobe activity, neo cortex activity, number of convultions, and, to a dashingly small degree, brain size. For all we know, the mighty blue whale might be about as bright as an ant. there’s also such things as the speed of brain processing. I have a brother who’s very intelligent, and was considered a bit mentally handicapped in school. Turns out, when they ran some tests on him, his retention, memory, problem solving ability, learning ability, were all on par with a good IQ-just the processing was slower.

  16. there’s no evidence for a decrease in the ratio of average brain size to average body size, which would seem to be what’s more an indicator. sure, human brain size has decreased 10% since the ice age 30k years ago, but so has body size.

  17. If the feeding advantage that a big brain gives you is not enough to offset the metabolic cost of a big brain, then the guy with a baseball for a head will thrive on calories that the guy with a soccer ball for a head will merely survive on.

    Ima bookmark this for the next time someone howls me down for being un-PC when I point out that all things being equal, stupid people do, in fact, breed more.

  18. Has nobody noticed that he’s got his dates wrong? Human beings were mostly nomadic, non-sedentary, and non-agrarian until the Neolithic Revolution. Don’t you love it when a television producer writes a biologically-based book full of bad behavioral anthropology, and fails to read anything recent from the world of archaeology? So much fail, so little time.

  19. I suspect that evolutions is working on human consciousness in a much more detailed level that simply scaling a brain up or down. For instance I’ve read that the gene for ADHD appears to be being selected *for* since around the time we started living in cities.

    Extreme ear of strangers would possibly be beneficial in a tribe, but lethal to a city dweller. I’d expect that to be selected against.

    And so on.

  20. Dang, too bad for my family of macrocephalics.

    This is an old theory, we’re also loosing our wisdom teeth, our males are more feminized, there is less sexual dimorphism. However, we also know that it’s energetically costly for very much sexual dimorphism in our progeny and there is far less differences between the sexes in developing countries and far more extreme differences in first world countries so there are some balancing selection occurring too.

    The most blatant and obvious aspect of infantalizing selection is the Kung! people, who both have little sexual dimorphism in the sexes both in societal roles and in physique, however they also retain large brain cases in comparison to their body size.

    I guess, for me, I have a hard time with this argument. Yes our brain size is less then H. neanderthalis and H. heidelbergensis, but we also have better specialization and theoretically more brain plasticity (based on tools) then either.

    Besides, macrocephaly is associated with high functioning autism and technology driven industries (i.e. Silicon Valley’s high incidence in progeny). Are the big heads sort of ruling the world anyway?

    – Ethel

  21. Perhaps the past 100 years of increasing urbanization has had an effect – but that widely practiced Human Endeavor of War surely had a distinctly opposite effect.

    I.e.: War as Good for the Species – if not the Individual

    1. War as Good for the Species – if not the Individual

      I’ve seen this argument before, but it strikes me as suspect on several points. If the argument is that warfare is a positive selective force for our species, what exactly is being selected for? The whole point of organized military is that training will make all soldiers more or less equivalent units. This means that death in battle is essentially a random event in that population, which means that all specific genes in that pool will be selected for randomly. All war does is reduce the total pool of genes that have passed the filter of being sound enough physical specimens to become soldiers in the first place.

      If you mean the reproductive enhancement granted to soldiers in cultures that glorify war, that is a slightly different question. Considering the environment that we now live in, are the characteristics most common in soldiers but absent or rare in the rest of the population actually “beneficial to the species”?

      It would make an interesting thesis for someone….

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