Slouching toward idiocracy?

By Razib Khan | December 27, 2010 1:32 am

The September issue of Discover Magazine had an interesting piece, If Modern Humans Are So Smart, Why Are Our Brains Shrinking? It’s now online, though to read the full article you’ll have to have a print subscription, or, pay 99 cents to get a digital copy of that issue. John Hawks is described as “a bearish man with rounded features and a jovial disposition.”

The background to this phenomenon is rather simple. For several millions years up to ~200,000 years ago there was a study increase in hominin cranial capacities. I say hominin because it seems that this increase was evident in all branches of the human lineage. Neandertals were increasing in cranial capacity, just as African humans were. Then there was a leveling off and stabilization. Finally, over the past 15,000 years or so there has been a decline, from a median of 1,500 cubic centimeters (cc) to 1,350 cc.

You can read the article for an elaboration on the various hypotheses. But roughly, some think we’re getting less intelligent, while others believe that the brain is reorganizing its structure and development. Remember that the brain uses about ~20% of our caloric intake. It’s a metabolically expensive organ.

I would like to add that even if the median human intelligence is decreasing, the current generation has the largest absolute number of very bright people alive at any given time. This is a natural function of the large human population. If the stability of civilization rests not on the median human, but the coordination and mobilization of large numbers of cognitively gifted humans, then perhaps we should not worry too much in the short to medium term. Even with stabilizing world populations we’ll have a generation or two of large numbers of brights before differential fitness of the smart and dull really start eroding the numbers of the former.

CATEGORIZED UNDER: Evolution, Human Evolution

Comments (36)

  1. Denis Vluegt

    Is it possible that women who bore large-cranium babies died often in childbirth and natural selection favored women who produced babies with smaller heads?

  2. J

    What is the correlation between cranial capacity and IQ in modern humans? I have read it is not very significant, which seems hard to believe, given the numbers of neurons in each cc.

  3. Jim Johnson

    Since I first heard of this, I’ve been wondering if what we’re losing is not “brain volume”, but “brain cushion”. I’m sure the paleontologists who study these cranial cavities know how to tell which parts shrank and so forth, but it certainly seems significant that the decrease in cranial capacity happened at the same time our species began harvesting less mega-fauna (and assumedly dealt with less head trauma as a consequence).

  4. Longma

    Are these cranial capacities measures adjusted for body size? I’m sure you are well aware that humans have also been moving toward a more gracile (albeit taller) form. I would like to see a side by side comparison overtime, to see if the decreases correlate. More to the point, is the decrease in brain capacity having to do with the decrease in size of certain areas of the brain that deal with motor control and senses, something we might not need in a modern world, but needed as a hunter-gather?

  5. The most interesting bit of this is how much it actually does conflict with the standard Idiocracy-type narrative. People who claim we are getting dumber generally try to argue that it is something that has started at most in the last few centuries (often just the last fifty years). That it might be something that’s been happening for 50,000 years? That doesn’t fit that narrative, most likely because that narrative is to a large extent a standard narrative about nostalgia, general decline, almost part of a fall from grace. People like that story in the general form, hence it shows up in a lot of religions. It especially shows up in Abrahamic religious, so people are steeped in that theme even if it normally focuses on moral decline rather than intellectual decline (although in Orthodox Judaism there is a notion of the “decline of the generations” which applies this much more widely to not just a moral decline but also a decline in intelligence and in general knowledge levels.) That sort of decline for 50,000 years though doesn’t fit that sort of story well since they can’t just blame it in video games or TV or the like.

  6. Matt

    There’s a video presentation by Professor Hawks here relating to this -

    The charts he references in this show no change in bone length in his Southern African San population, though I don’t know if that is universal. I remember reading that at least relative limb proportions are more complicated in other parts of the world, due to climatic adaption. That also seems that it doesn’t tell you what Fat Free Body Mass would be like, and that’s what’s important. – This paper has estimates of stature and body mass for Paleolithic, Mesolithic and Neolithic to Bronze Age Europeans. Doesn’t look like a strong change in BMI, although absolute body mass and height look like they changed more, but with no real strong trend.

  7. miko

    There has been some recent coverage of the apparently surprising-to-some finding that “group intelligence” (a somewhat new concept which I think is so far poorly defined) is not correlated with mean, median, or maximum IQ of individuals in the group, but rather with structural features of the group and its dynamics. I’m not conversant with the details except that this is for small groups and specific kinds of tasks, but if you’ve ever seen a bunch of physicists trying to switch out a liquid nitrogen tank, well….

    The mapping between individual intelligence and the “cognitive abilities” of groups on various scales (family, tribe, society, civilization) is probably is not simple or linear. Particularly at larger scales, group achievement may depend on structural dynamics, how work and information are organized, etc, far more than average ability. The shipping department (no offense!) works orders of magnitude more efficiently and “smarter” than any academic department I’ve ever seen. Every company in the world knows it is useless to just hire smart people, you need an organization that exploits a range of talents from diverse types of people. I know if you pick people to work in a collaborative research lab based on grades and standardized test scores, you’re doomed.

    Anyway, point being… maybe once you have “smart” organizations, smart individuals become less advantaged relative to others. To be “parsimonious,” however, I would say skulls have functions beyond enclosing brains, my instinct is to be dismissive of any conclusions about trends in cognitive evolution based solely on hat size. Even if IQ does vary weakly with skull size within a particular hominid group at a particular time does not support the idea that it correlates across related species.

  8. Mark


    I think you can make a good argument that the advent of contraception accelerated any pre-existing decline in intelligence.

    I’m not too comforted by the fact that there are millions more smart pekoe then ever before. Smart people don’t exist in a bubble. A lot of their otherwise productive efforts are gong to be going toward alleviating the living conditions of many more millions of their less intelligent cousins.

  9. occamseraser

    This is actually old news.

    Nature 387, 173 – 176 (08 May 1997); doi:10.1038/387173a0

    Body mass and encephalization in Pleistocene Homo

    Christopher B. Ruff*, Erik Trinkaus† & Trenton W. Holliday‡

    Both brain size and body size have decreased over the last 35ky according to this study. “Relative” brain size, not so much.

  10. bioIgnoramus

    “hominin” is a pleasing word that has rather sneaked up on me. Can we agree to call chimps and gorillas “hominouts”?

  11. JMW

    Studies have also shown that the cranial capacity of modern domesticated cats is smaller than that of domesticated cats during the classical Egyptian period. Similarly, domesticated cattle have smaller cranial capacities than their wild cousins.

    So one possible factor contributing to the decline is that the human race has domesticated itself. We no longer need to use our wits to survive in the wild; hence we need less cranial capacity for processing information related to hunting/being hunted. As you remarked, the brain is a metabolically expensive organ, so it would make sense to reduce its drain on the energy budget as much as is possible.

    This is a factor that would have appeared only in the last 10,000 years or so, and is obviously not the only factor in the decline that started 50,000 years ago. It could also be that the domestication of dogs contributed to the original decline, as dogs took over many tasks that humans had to do themselves (hunting, scouting, herding). That says a lot about the effect of supervisory work on your brain…

  12. dave chamberlin

    So in the Idiocracy clip above what does the retarded president say to the world’s smartest man? “I thought your head would be larger.” It is funny because it is so rediculous.

    Did anything else happen right around 50,000 years ago? Wasn’t that right about the time of the “the great leap forward” when evidence of truly modern intellence started showing up in the archeological record. I never much liked the title the great leap forward, more like a conceptual threshold passed on a six million year walk in my opinion but still damn noteworthy. I’m not going to speculate as to why brain size stopped growing and even reversed when we started showing signs of using our brains in a modern creative way because I don’t know, but I very much doubt it is a coincidence.

    A second seperate subject covered above is our intellectual future. I remember years ago reading “The Bell Shaped Curve” and if I am not mistaken the book said women with graduate degrees are averaging 1.5 children while women who dropped out of high school are average 3.1. Even assuming that there is only a small correlation between education and inherited intellence and this two to one ratio gets greatly decreased the picture gets ugly in just a handful of generations. I’d put in a clip of Devo singing “are we not men, we are devo” if I was Razib at this point. But even if the average intellegence starts declining after the Flynn effect has reached it’s maximum there is another big change in our mating behavior that needs to be noted. The long term effect on the bell shaped curve on human intellence will be changed by college entrance exams and equality towards women. It wasn’t until after World War Two that smart women and smart men were accepted into the best universities because of their perfomance on college entrance exams. Before this time you got into Harvard because your Daddy did. So who are the very brightest men and women of today picking for mates? Their peers in the acedemic and professional world. So even if those without will who can’t swallow a pill inherit the earth rather than the meek, we should still keep our population percentage of nerds and it may even increase. The way genetics is moving forward these days, kind of a Moore’s Law in the fast lane, it isn’t far fetched science fiction to begin speculating that we will get that three pound thingamajigger between our ears figgered out so the idiots have the choice of mind glasses at birth for their kiddies, but what the hell do I know.

  13. I highly suspect that JMW is right. Modern human’s are Homo erectus that have undergone domestications syndrome. We’re the border collie to our wolf ancestors.

  14. This is actually old news.

    if you read the article you see people with paleontlologists with doctorates discussing this seriously and not dismissing it. if you can do so with a cite to a 1997 paper, that’s fine. perhaps the paleontologists are full of it. or perhaps it’s a little glib to just cite an old paper to dismiss? unless that is you have specialized knowledge in the area?

    What is the correlation between cranial capacity and IQ in modern humans? I have read it is not very significant, which seems hard to believe, given the numbers of neurons in each cc.

    30 seconds of google books would have yielded a correlation between brain size and IQ of 0.3. prolly be lower for cranial capacity. that’s a rather small r-squared actually, huh?

    many of the points made in the comments here are addressed in the article. since discover puts some bread on the table for me it’d be churlish for me to just repeat everything which was gained through genuine reporting. sorry 🙂 is $1 so much if yer curious?

    So even if those without will who can’t swallow a pill inherit the earth rather than the meek, we should still keep our population percentage of nerds and it may even increase.

    yeah, i was hoping assortative mating would be our salvation. unfortunately i don’t quite see that it has a large enough impact last i checked.

  15. It especially shows up in Abrahamic religious, so people are steeped in that theme even if it normally focuses on moral decline rather than intellectual decline

    not that this matters, but from what i know this is wrong joshua. most world traditions are explicitly declinist. confucius looked back to the golden age of the sage kings. his project was one of restoration. and we famously live in the kali yuga. the greeks believed that we had declined from ages of gold, to silver, to bronze, to iron. in fact, many scholars have argued that abrahamic religions are more progressive, and implicitly less declinist, because they have a projection of future religious utopia with the messianic age.

  16. related: natalie portman is pregnant.

  17. Rafe

    JWM and Dave Both hit on key concepts here.

    Its not just cats, cattle and humans, in fact the relative brain size of almost all domesticates is smaller then their wild ancestors . This just part of a suite of changes that characterize domesticates. Including reduced size, a more pronounced forehead, a shorter foreface, overall increased morphological diversity, a wider range of coat colors, long hair, curly hair, naked skin, and reduced dentition. Most of these characteristics are seen in modern humans relatives to our ancestors. Compared to erectines and neanderthal and even early AMH modern humans are less skeletally robust, have shorter forefaces and larger foreheads and smaller teeth in more crowded jaws. Compared to chimps we are characterized by being having naked skin, long hair of an astonishing variety of color and form and increased morphological diversity even within genetically homogeneous populations.

    The belyaev Domestic fox experiments, provides a very intriguing clue as to why this might be. Belyaev was able to induce all of the morphological changes typical of domestic animals in foxes by breeding for a single characteristic, Tameness. Tameness can be conceived of as openness to novel social situations and strangers. This is characteristic of all juvenile animals but rare in adult wild animals. Selection for this trait seems to effect developmental genes which have major effects in morphology resulting in these typical patterns of morphological change.

    Domestic animals are generally less intelligent then their wild ancestors but they appear to have domain specific capacities for social learning and thinking that their wild ancestors don’t

    I suspect that the development of just such capacities as been one of the primary selective patterns behind the development of modern humans. We may have lost some individual brain power but without the evolution of those social capacities I doubt we would have ever been able to harness that brain power to build civilization. I also think it’s quite likely that the selective environment of civilization has selected for a horde new adaptions on traits like IQ and time preference which would have not been as advantageous for our paleolithic ancestors.

  18. you’re definitely in the ‘bluebird’ group of commenters for that rafe 😉

  19. RT

    A similar thought to Longmas that the decrease in cranial capacity may have something to do with the decrease in size of certain areas of the brain that deal with motor control and senses as opposed to cognitive ability (g) occured to me. It would be interesting to know how different regions of the brain expanded or contracted over time. When reading about Jung and Haier’s P-FIT (Parietal-Frontal Integration Theory) based on their neuro-imaing studies linking the parietal and frontal lobes as the regions of the brain most strongly connected with g, two things I had read previosly immediately jumped into my mind:

    1) Thumbing through old anthropology books like Coon I’ve read that over historical time frames Europeans (and I believe also East Asian populations) have become increasingly brachycephalic (broad headed) and even allegedly long-headed “nordic” populations like the Dutch, Danes and North Germans have a mean cephalic index of 80 or more, making them low brachycephals. In contrast, most ancient Europeans were dolichocephals. To me this brachycephalization sounded like it could have been caused by an expansion of the parietal region, perhaps combined with a contraction of the visual processing sections in the back of the head.

    2) In “The 10,000 Year Explosion” Cochran and Harpending note that over historical timeframes the cranial vaults of the English population have become higher and more vertical, despite no significant immigration since the Dark Ages. This sounds like an expansion of the frontal region of the brain and is also in accord with an increasing average cranial vault height over time noted by early 20th C. anthropoligists like Coon.

    Perhaps modern man, at least in some regions of the world, has seen an expansion of the frontal and parietal regions associated with g, and a decrease in the areas that deal with processing sesory information located mainly in the back of the head?

  20. miko

    “frontal and parietal regions associated with g”

    “the areas that deal with processing sensory information located mainly in the back of the head”

    Those are two new exciting findings in Neuro-Science. Anatomic correlations with IQ are dynamic with age–a bit troubling for suggesting an anatomical location for g. Chemosensation is certainly the oldest sense and the most important in most mammals–check out where you olfactory bulb is. In one simplified sense, one might consider the thalamus the central sensory processing area, it’s basal but not in the back. Cortical sensory maps are all over the place, mainly middle-ish.

    If the domestication model extends to humans, one would think skull morphological change is not due to selection for brain shape but an incidental byproduct of altered neural crest development due to selection on endocrine systems.

  21. occamseraser

    @rk: I didn’t dismiss it at all. It’s just not news, as you would discover if you had the time/took the time to read it. It’s a classic, very important paper that your readers might find of interest and relevance. Hence the citation. The implication is that the reduction in brain size is a correlated response to reduction in body size, although as Russ Lande and others have noted, the intraspecific genetic correlation between these 2 variables is not terribly high.

    BTW, I’ve been a practicing, publishing biological anthropologist since I received my Ph.D. in the mid 70s. Sometimes you get defensive for no good reason. Like this time.

  22. It’s just not news, as you would discover if you had the time/took the time to read i

    it says it’s not news in the discover article. and of course i knew about the general result even before the article. i’ve blogged about it before. e.g.:

    i said it was interesting. not novel. i’m not defensive, i just hate commenters who pop off without even bothering to read what i link to. even the free part of the discover article makes it clear that this is a well known phenomenon among paleontologists, if not the general scientific public. if you paid $1 you’d see that the anthropologists know about the issue about correlation with body size (that’s biology 101), but they don’t think that the data is so clear that that can explain the whole phenomenon. since you have a ph.d. in biological anthropology, and have been a scientist longer than i’ve been alive, have the data sets since 1997 not changed the picture at all?

  23. here’s the fucking quote btw:

    “Since the Bronze Age, the brain shrank a lot more than you would expect based on the decrease in body size,” Hawks reports. “For a brain as small as that found in the average European male today, the body would have to shrink to the size of a pygmy” to maintain proportional scaling.

    Hawks chose to focus on Europe in the relatively recent past, he explains, because there are exceptionally large number of complete remains from that era. That allowed him to reconstruct a detailed picture of what was happening during our downsizing. The process, he discovered, occurred in fits and starts. There were times when the brain stayed the same and the body shrank, mostly notably, he says, from the Roman era until medieval times. But more frequently, the brain got smaller while the body remained the same. Indeed, Hawks says, that is the overarching trend for the thousands of years he studied.

    granted, john only got his phd in 1999.

  24. Miley Cyrax

    Holy shit!

    …Natalie Portman is pregnant?

    But on cranial capacities throughout time, this trend should be helped along nicely by those in the lower socioeconomic classes pumping out babies left and right, many of which on the government dole… while higher class couples put off having kids only to have trouble conceiving later on in the woman’s reproductive lifespan.

  25. T. Kosmatka

    RT: “the cranial vaults of the English population have become higher and more vertical, despite no significant immigration since the Dark Ages. This sounds like an expansion of the frontal region of the brain and is also in accord with an increasing average cranial vault height over time”

    –I suspect any increase in vertical foreheads has more to do with decreasing facial robusticity than increasing brain tissue.

    Neanderthals are a great example of this. They have sloped forehead because their faces are massive, not because they have small forebrains.

  26. Razib, good point. I’m completely wrong about that being more the case with the Abrahamic religions.

  27. josh, props for admitting error.

  28. biologist

    It’s a real puzzle actually.

    Overall brain size correlates about 0.4 with IQ among contemporary adults of the same sex, and increasing brain size is associated with apparently increasing behavioral complexity in human ancestors (and other lineages).

    That leaves wiggle room for economizing mutations to account for some of the shrinkage, and certainly men and women achieve similar outcomes in terms of g with different sized brains.

    But it’s hard to get around the possibility that we’ve lost some cognitive capabilities since the peak.

  29. Andrew Lancaster

    1. Someone mentioned this is old.

    In my humble opinion one of the problems with many discussions of this subject is however the media and general public’s misunderstanding of the “selection” metaphor, meaning that devolution is thought of by some people as the opposite of selection, which is kind of weird if you think of what selection really means in biology. It is therefore very much worth reading “proper” biologically correct discussions of the subject.

    2. Social intelligence.

    We shouldn’t be too happy with any idea that some type of social intelligence is a good thing to be getting instead of the old fashioned type of intelligence which gets in the way of division of labour. Consider how much ants and bees have. They certainly seem to demonstrate that hive minds do not require a hell of a lot of brain power amongst individuals.

  30. occamseraser

    I look forward to examining JH’s data base and analyses in a peer-reviewed journal article, especially how the knotty problem of reconstructing body mass for dead people was solved. Check out this ref to see how other scientists approached this challenging problem for a mid-Pleistocene Asian fossil in PNAS of Feb, 2006:

    “Body size, body proportions, and encephalization in a Middle Pleistocene archaic human from northern China.”
    1. Karen R. Rosenberg
    2. Lü Zuné
    3. Christopher B. Ruff

    Glad to see we agree that, fundamentally, this story is indeed “old news”. I never implied that the phenomenon was fully explained by genetic correlations between body size and brain size. New data and new spin are always welcome, even if they appear in a pop sci forum.

  31. Pat Shuff

    …there is a greater “packing density” of the neurons in the female brain.

    The male brains were about 12.5 percent heavier than female brains. Hence the greater neuronal packing density in the female brain nearly balances the larger size of the male brain. The g Factor; Jensen pg. 149


    Always knew she was denser. Perhaps these sorts of changes are involved.
    Fwiw, I find claiming Neanderthal heritage does injustice to Neanderthals!

  32. BrianDH

    Most of the comments I wanted to make have already been expressed by others; the others are as of yet quite undeveloped and likely wouldn’t add much to the discussion.

    That said, for the edification of anyone interested, the following is IMHO a very good review of some of the neuroscience topics at hand here:

    I am especially interested in the potential for developments in this area wrt functional connectivity (as inferred via DTI and resting-state fMRI), especially given that the lab at which I am an assistant is currently performing heavy research wrt the so-called “default network” (there is some controversy that moniker — my PI, for instance, despises it).

    Note that there is a non-paywalled copy of the paper on the website of one of the authors; however, I know not if he has permission to distribute it, so I will leave it to the interested to seek it out themselves.

  33. Doesn’t this also roughly coincide with a period of significant retreat of ice as the interglacial (Holocene) took hold? Maybe we really are (or were) living in a uniquely halcyon climate, if such has any influence on the size of the brain required to survive.

  34. Chibble Dibble

    This is really terrible news for 19th century craniometrists!


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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at


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