Gene Expression

Encephalization, why?

Between 3 million & 200,000 years ago the average cranial capacity of this planet’s dominant hominids increased along a upward trendline, in starts and stops. Bipedal apes went from having nearly chimp sized crania to one similar to modern human beings (Neandertals had larger brains that H. sapiens sapiens). Symbolic culture as we know it though seems to really explode (a.k.a. “The Great Leap Forward”) between 50,000 and 30,000 years ago. There have been many books on these issues. The Mating Mind, The Prehistory of the Mind and The Dawn of Human Culture hit many of the controversies from a popular angle. Nevertheless, what do you think happened??? Was it climate change (I’m skeptical)? Was it some sort of cultural ratchet? Was it God?

Update: Brown guacho has a long post with graphs and pictures. Highly recommended.


  1. #1 skblllzzzz
    May 17, 2006

    In the old days (1990-ish?) I had on my Amiga computer a program that allowed one to drag a pointer along a time line which caused a skull to evolve or regress. Very informative. Does anyone know of something similar for OSX?

  2. #2 IndianCowboy
    May 17, 2006

    Personally I’m somewhere between the ‘language’ and ‘ah screw it we’ll never freaking know’ categories. Which seems to be the consensus with most of the bioanthropologists and students I’ve talked to about this. The recent genetic studies do reveal that we likely had the capacity for language more than 100,000 years ago, but that’s not the same thing as actually using it.

    From the skeletal anatomy, and probably the genetic evidence too, I just don’t think we can point to a new trait. Climate change is dicey too because IIRC, most of our symbolic finds have not been in the ‘pretty’ places

  3. #3 IndianCowboy
    May 17, 2006
  4. #4 Ahcuah
    May 17, 2006

    My suspicion is sexual selection, based on the development of a trait allowing the recognition of intelligence along with the realization that intelligence improves one’s chances of raising children to adulthood. If those with intelligence preferentially mate with others in whom they recognize intelligence, then they will be able to outbreed those who don’t have the intelligence. And by intelligence I mean things like the logic required to do the problem-solving that keeps one alive.

    From there it snowballed, and we get things like art and music and mathematics as proxies for demonstrating our fitness when it comes to intelligence. Our intelligence is a peacock’s tail.

  5. #5 mythusmage
    May 17, 2006

    Creativity really got its start around 56,000 bp when 10 year old Thrug claimed Dad’s flint knapping tools had been messed with by maniacally giggling baboons; when the actual culprits where mildly amused macaques.

  6. #6 Christopher Gwyn
    May 17, 2006

    There were probably several reasons that things happened as they did. One of them, in my view, was a ‘software problem’. Language was something that we had to create, and as language developed we had to accumulate enough information to pass onto each other that we crossed that vague line between ‘animals with habits and tricks’ to ‘people with cultural tools’. We don’t easily realize the role of language and culture in being able to think because we have such finely developed ‘cultural tools’ to pass on to children or strangers who move to town. But it took awhile to learn…

  7. #7 Dan Dare
    May 17, 2006

    Didn’t you see the movie; “2001 – A Space Odyssey”….?

  8. #8 carey allen
    May 17, 2006

    Certainly there were several factors. Sexual selection can lead to some very rapid changes. Consider our deep-seated love of music and story-telling – they are literally bred into us through thousands of generations of sexual selection. Tool-making, etc, get a lot of attention, because we can hold the artifacts. Sexual selection that took place around the evening fire left no artifacts, and so is easily overlooked. Sexual selection for a pleasing vocalization could very quickly result in a much more precise vocalization, which in turn facilitates the development of language. These threads are not separate – they run together.

  9. #9 razib
    May 17, 2006

    carey, remember that sexual selection often implies sexual dimorphism unless you are talking runaway, and runaway is usually so fast it is like like a snap.

  10. #10 rjb
    May 17, 2006

    An interesting thing to consider is that similar rapid evolutionary changes in brain region volumes occur in insects. An article in PNAS by Farris and Roberts shows that generalist feeding ecologies are correlated with increased size of insect mushroom bodies (a sensory integration region of the brain) across taxa. Within a taxon, there can be quite dramatic differences in brain volumes, suggesting that this is an evolutionarily labile trait. So the rapid evolution of large brains is not unique to the hominid lineage.

    Farris SM and Roberts NS. 2006. Coevolution of generalist feeding ecologies and gyrencephalic mushroom bodies in insects. Proc. Natl. Acad. Sci. USA 102; 17394-17399.

  11. #11 IndianCowboy
    May 17, 2006

    Carey, just one problem with that that I can think of. I only had one class in cultural anth but I can’t think of a single H/G tribe where rites of passage, and mate-choosing ceremonies deal directly or indirectly with intelligence.

    The only culture I can think of where that’s even remotely true is in my grandmother’s head as she tries to line me up arranged marriage prospects.

  12. #12 Boknekht
    May 17, 2006

    Is it unlikely that human intelligence evolved through sexual selection?

    If it was natural selection then things like clever war strategies & food finding allowed the more intelligent to survive at higher frequencies throughout prehistory, progressively increasing encephalization?

    How many neurons per generation(on average) have been added within the past 1million years of hominid evolution, for an increase in encephalization from ape-size to our current size? I thought i saw this somewhere before.

  13. #13 Agnostic
    May 17, 2006

    Cranial volume may be larger in Erectus, but do we know that that means brain volume is larger? The 2-D sheets of our cortex are packed very densely inside our skull, like a napkin wadded up to fit in your paper cup. Depending on how densely you pack them, you could wad up 10 napkins into smaller cup and 8 into a larger cup. Cup size is deceiving when you look cross-species. Human brains we can examine & see all the resultant wrinkles, but is there similarly robust data on Erectus cortices? I googled & found nothing, but it was a casual search.

    As for why greater encephalization trend? Dunno, but as a linguist, I should promote my tribe and say “language.” If not the modern version we know & love, then a more primitive version, perhaps where there were only pidgins (the languages that two different linguistic groups use when they first meet — super-simplified).

  14. #14 Agnostic
    May 17, 2006

    And btw, whenever I hear suggestions that braininess evolved due to its sexiness, I can’t help but think it’s retrograde wish-fulfillment on the part of nerds & loner artists. To the extent that braininess leads to higher status in males, then braininess would correlate w/ sexiness in males — but I think cunning interpersonal skills, Machiavellian intelligence, and outright physical dominance were better predictors of who would be Top Dog 500 kya.

    Since both a male’s intelligence & status rank aren’t terribly difficult for females to figure out, they should evolve to home in on whichever is more important for his & her kids’ fitness, should the two cues send mixed signals. I don’t know how females 500 kya ago would’ve responded, but would the average female now choose a guy who had 0 SD intelligence but +1 SD status, or vice versa? Keep dreaming nerds & artists!

  15. #15 razib
    May 17, 2006

    re: sexual selection again, please note that human sexual dimorphism is rather minimal re: size, and we don’t have big canines (as males) like other apes. we could be dimorphic in other ways…like males being very artistic or something. that’s geoff. miller’s idea…but i’m not convinced because of agnostic’s reason. i an intrigued by the ‘generalist’ idea, as i don’t think there will be ‘one trait to rule them all’ the more and more i look into this.

  16. #16 Boknekht
    May 17, 2006

    re.Machiavellian intelligence & physical dominance,

    i wonder what kind of society we lived in 500 kya? We were erectines(word form?) back then, i guess.
    But how did these erectines organize themselves socially? I wouldn’t think that they lived in nuclear families. Were they as machiavellian in behavior as are Chimps or any other beast of nature? female primates are display machiavellian character. I can’t make any educated or informed guesses here, but these are highly interesting questions to me.

    “Keep dreaming nerds & artists!”

    Hey!!!, Agnostic!!!
    I’m not a nerd or an artist, nor am i what could be called a geek(i actually hate reading & books; i just like the data they contain), but i do worse with women than they do. I’m a very good-looking guy, to myself & my fam at least, but i just can’t deal socially with women, & the introversion doesn’t help(but i still like being introverted:). I don’t even have any male friends/buds. Plus I’m low SES, have a small head, & have a lower than room temperature IQ, judging by the academic programs schools kept me in. My mom says i stopped growing for a while when she was pregs with me, & that the docs were concerned. That might have affected my brain & done me in intellectually. But, maybe not.
    I’m the product of a mom who’s extra-extra dumb, & a father who’s extra-extra smart(142 IQ). So i might have regressed far+the pre-natal issue. Who knows:)

  17. #17 Ahcuah
    May 17, 2006

    When we’re talking intelligence here, we’re not talking nerds. We’re talking about distinguishing chimp mental acuity. We’re talking about the ability to create a roof that doesn’t leak from twine and bamboo. We’re talking about the ability to weave fabrics from twine created from scratch. We’re talking about the ability to figure out the knots to weave a hammock.

    And if prospective mates recognize that ability, that makes the mates more valuable, in that those sorts of things really help getting a child to adulthood. And if the ability to hold a tune, then create a tune, then to create a complex tune becomes a proxy for demonstrating that intelligence, then the sexual selection can really take off.

    Regarding tribal rites of passage, it’s not the intelligence that is being looked at, but the proxies for intelligence. Even in the 18th century, women would do all sorts of needlework and tapestries that demonstrated their “intelligence”, i.e., ability to care for and raise children. In fact, even participation in a ritual, showing the ability to memorize specific rites and sequences acts as a proxy for the intelligence needed to raise human babies.

  18. #18 Agnostic
    May 17, 2006

    We’re talking about distinguishing chimp mental acuity.

    Ah, but we were talking about what accounted for the spike in encephalization millions of years after the split from chimp ancestors; say the inflection point was 500 kya. By then being able to weave was unremarkable, so “braininess” has to mean “brainy for a hominid 500 kya.” OK, so that’s not being able to do higher math, but still something impressive.

    And as Razib keeps saying, where’s the dimorphism that you find with height or aggression? Greater variance, sure, but for IQ, musical ability, etc., it’s not as if the male median towers above the female median.

  19. #19 SkookumPlanet
    May 17, 2006

    I’m a bit confused. Is the question about encephalization, roughly post-Australopithecines to modern Homo, or the “Big Bang of Culture”, or both?

    I’m struck by the coinciding start of our cyclical ice ages 2 – 2.5-mya and the emergence, in east Africa, from the under-4-feet-tall, chimp-brained but bipedal, australopithecines, Homo Erectus, which is our body plan topped with an intermediate brain size inside a chimp-like head . To call this a connection to “climate change”, etc. mischaracterizes it. Regionally, it would likely manifest as incredible ecological volatility created by the multiple abrupt climatalogical changes inherent in getting into and out of the more stable ice ages and interglacials — changes on the scale of decades, not centuries.

    Is it also possible the emergence of Modern Homo Sapiens is tied to one of these transitions? As a concrete example, a tribe of archaic Homo Sapiens could have seen their regional wooded environment change to semi-arid brush in the span of a generation. This would have favored the ability to rapidly shift the means by which such tribes’ environment was exploited. Different animals, different plants, different seasons.

    Pursuing links here I came across a specific study in PNAS looking at this question in birds, which found evidence of the connection. But much more interesting was a commentary on the study and it’s importance, which summarizes recent research…

    Various measures of brain size (e.g., encephalization quotient, brain-body residuals, neocortex ratio) are positively correlated with feeding innovation, learning, and tool use in birds and primates; behavioral repertoire size in mammals; social complexity in birds, primates, carnivores, and some insectivores; dietary complexity in primates; and unpredictability of the environment in hominids.

    …Furthermore, these findings are consistent with a general “behavioral flexibility” hypothesis that says that large brains confer an advantage when responding to variable, unpredictable, and novel ecological demands through enhanced behavioral flexibility, learning, and innovation.

    …The authors demonstrate that powerful tests of hypotheses can be performed by using archived data that is quantifiable and ecologically relevant.

    …In both birds and primates these areas of the brain are the “on-line” executive processing regions allowing for opportunistic solutions to new problems. It makes sense, then, that an environment doling out uncertainty would encourage the enhancement of the very part of the brain that copes with uncertainty.

    … and it closes with …

    Their approach offers us the potential to compare a wide range of different animal groups. So far, only birds and primates have been dealt with in this manner with any degree of depth. But there are other taxa, cetaceans, carnivores, perhaps even invertebrates, that are intriguing and critical comparison groups for gaining a handle on whether there are truly “universal” patterns of causation across brain, behavior, and ecology on Earth.

    So, with the appearance of genus Homo we have the two ingredients, encephalization and hyper-novelization of environments.

    As for the “Big Bang”, I read The Prehistory of the Mind last fall. I like Mithen’s idea that the development of full language capability may have given us the ability to intermingle cognitive domains, and thus culturally explode. Intuition tells me if the similar timing of language acquisition and culture blow-out holds true, it’s likely to be a non-trivial connection.

    And as for brains being selected for as sexy? Think about the products of brains, not brains. As a fertile female contemplating ultra-dependent infants, which do you go for? A local provider with the regular roadkill, or the guy from the neighbor tribe with something new, a bone-bead necklace with a sabertooth saber strung in the middle? The big bang of 50,000 BCE included the dawn of adornment. Soon [geologically] we’ve got lipstick, bikinis and do rags.

    Hey, some of us still think brains are one of the hottest items in our inventory.

    The commentary is definitely worth a look and is dead on this topic.

  20. #20 IndianCowboy
    May 17, 2006

    Razib, size dimorphism is still pretty big. It doesn’t look that way when you do cross-cultural studies, but within a given H/G tribe or any relatively homogenous group there’s decent separation; especially in those cultures where physical prowess is a part of daily life for both male and female. Strength dimorphism is even greater than size dimorphism.

    This is one area where you definitely don’t want to be looking at a bunch of Americans and generalize from there. At 210lbs of mostly muscle I’m a big guy, but I certainly doubt that I’ll have any more reproductive success than a guy who’s only sayyy 165lbs. IN fact some of my friends from high school about that weight have already had more children than I ever plan to. Same holds true for other traits. Does anyone really thinkg there’s a correlation between reproductive success and intelligence?

    Remember that apes have less canine dimorphism than body dimorphism as well, and less than one would expect using a general anthropoid trendline.

  21. #21 IndianCowboy
    May 17, 2006

    what’s wrong with do rags? I have a couple.

  22. #22 razib
    May 17, 2006

    Razib, size dimorphism is still pretty big

    just to be clear, i mean sexual dimorphism (in reference to sexual selection). my understanding is that it is not that big (15% or so?).

    Does anyone really thinkg there’s a correlation between reproductive success and intelligence?

    the past is not the present. remember that in the victorian era the high SES females were baby factories while low SES barely replaced.

  23. #23 SkookumPlanet
    May 18, 2006

    I didn’t mean anything pejorative about lipstick, bikinis, or do rags.

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