Brain shrinkage in humans over past ~20 000 years—what did we lose?
The human brain volume has been shrinking over the past 20 000 years or so, after millions years of increase in volume. Not just the brain size, but the brain size relatively to body size as well. We are lacking a tennis-ball sized piece of our earlier brain (and it might even be God-shaped).
Brain is expensive in many ways: energy consumption, birth complications and locomotion impairment for females, lower survival of head impacts i’d guess. The damn thing along with supporting structures is heavy and awkwardly located, etc.
And the big brain can only be advantageous if it improves reproduction substantially, with larger brained individuals being sufficiently more successful at surviving and reproducing than smaller brained individuals, as to negate the above-mentioned cost.
That must have been the case through the evolution up to a couple tens thousands years ago, to produce the big brains that we have. It is clear to see that in past 20 000 years, the environment in which humans live has undergone very significant change due to emergence of societies; the new environment may not be pushing us as hard [in the direction of intelligence], at least on the individual level. [and may have been pushing us too hard for smaller brains, thanks Nornagest for making that point]
We were evolving ability to think, until it got just about to the point of being barely able—with great difficulty and many falls—to think useful thoughts. If we were species that were evolving flight, we’d be the species that could just barely fly, and recently flew over a river, entering new land. In the new land, everything is different. And our wings were shrinking at very rapid rate.
The important question is—Did we lose any functionality since then? Are we dumber? Are we less sane in some way? (The palaeolithic humans did not seem to do any really insane religious stuff)
The notion that our brains just got more efficient and ‘therefore’ could shrink in size appears very shaky to me. This ‘therefore’ comes from fallacy of anthropomorphizing the evolution. Evolution doesn’t work to a goal of optimizing some sub-unit in the organism while preserving specifications, in the way that a team on an engineering project would.
The optimization could as well instead make brain even larger, if said improvement made larger brain pay off more. One would have to show that some improvement in brain efficiency has actually decreased advantage of big brains over small brains, to explain the smaller brains with them being more optimized.
The evolution optimizes the whole organism, not the brain, and there’s very many of other factors that have changed at that specific time that may as well have decreased selection pressure towards intelligence or increased the costs.
In my opinion the sensible default hypothesis should be that we had a decrease in some functionality, and likely are still declining.
My best guess is that it is the capacity to invent solutions on spot and think by ourselves, that we are losing. Before emergence of societies, the technological progress was severely limited by information loss. Any smart individual could massively improve fitness of the relevant genes by (re)inventing some basic, but extremely effective techniques, which he’d teach mostly to genetically related individuals. The technique would easy become lost, creating again an opportunity for intelligence to succeed—reinventing it.
Even very simple invention requires massive search in the vast space of possibilities. Precisely the kind of task that one would expect to benefit from larger raw computational power.
edit:
Some clarification with regards to the need for innovation. In the long run, it is not enough to just do what you’re taught. Teaching is a lossy process. You need to improve upon what was taught to you a little to make the tool as good as your ancestor made—you need minor innovation to merely preserve the tools—a little more innovation and you’ll improve over time, a little less and you’ll lose it over time. The little children have to figure out everything from a few clues; they don’t download some braindump of the wisest elder to be able to speak, they essentially figure out an alien language—a very difficult task.
I’m not an anthropologist, but one plausible explanation I can think of for the brain shrinkage is almost diametrically opposed to this. It’s pretty well established that early agricultural societies placed more nutritional stress on their citizens than the hunter-gatherer lifestyle that preceded them; height and various other nutritional proxies consistently went downhill after the agricultural transition and in most places didn’t make up the difference until the Renaissance or even later. Brains, as you say, are an energy-intensive piece of equipment; and agricultural productivity looks a lot less elastic with regard to intelligence than hunting or foraging. Put that together and you’ve got a pretty strong argument for negative selection pressure w.r.t brain size, at least until industrialization got rid of most nutrient constraints. I wouldn’t even be too surprised if this was responsible for part of the Flynn effect, although there are certainly other factors involved; Flynn’s working too fast for selection pressure alone.
On the other hand, the Neolithic Revolution occurred about 10,000 BP, and the linked articles talk about a timescale twice to three times that long. They’re fairly short on details, unfortunately; I can think of scenarios that’d make that consistent with my theory, but this wouldn’t by itself explain a peak at 30,000 BP.
I believe that in some cases (eyes for cave-dwelling animals? antibiotic resistance in bacteria?) a trait can be turned off rather than lost completely. This means it would be easier to get it back than to evolve it from scratch.
Good point about the higher pressure to conserve the nutrients. Essentially, it’s a matter of relative selection for whatever aspects of intelligence rely on brain size, versus the selection to conserve nutrients.
With regards to being pushed by nutrition… The population can be expected to quickly rise to equilibrium level where the nutrition limits the population. At equilibrium level, the hunters would be bigger and stronger (and perhaps brainier) than farmers, because the farmer that starved this much will survive and the hunter won’t. All while both societies have their population capped by available nutrients.
The transition and preadaptation to agriculture might have taken several thousand years.
Not to mention it happened in several different places, at different times.
Except most discoveries which might confer a decent amount of fitness—enough for fixation to have a chance—are rare. For example, Tasmania had a population of thousands, yet they lacked almost all technology, and couldn’t even make fire (instead relying preserving existing flames); if anywhere someone would be inventing technology to help their kins, Tasmania should have seen such secret wiles. But no.
(This is part of a general argument against individual selection for innovation: innovation is too rare, and diffuses too rapidly to unrelated or barely-related people, to be an advantage for the individual—however excellent it is for the group.)
Minor innovation. Try attaching stones to sticks for example; humbling experience; I’m pretty sure you are going to get pretty strong correlation between even such modern measure as IQ test, and how well the stone stays on the stick.
For Tasmania, the population of thousands is insufficient to preserve genetic diversity and counter the drift, as the article you linked to itself says. The niche that made us intelligent is very unique. Put us into another niche—especially, a well isolated niche with little competition—and we may well de-evolve. Bird species that come to an island that has few predators using their flight, may not need to fly any more—same for intelligent species that figure out a way to get onto an island.
The usual trend with such things is that IQ correlates with speed of learning, with a ceiling effect; the high IQ hits the ceiling faster. It’s not at all clear that for simple tasks like stone on stick that the investment is worth the additional speed—what else are Tasmanian islanders going to be doing?
I think even in far limit higher IQ’s stones will stay better on the sticks. It ain’t easy to attach a stone to a stick well. It isn’t some well controlled industrial process here that you can figure out better. One day you have one stick, other day you have other stick. We rely on modelling of reality inside our heads to make items—seeing in mind’s eye how it would detach if the wrapping is in that particular place, but would stay on if its in another place.
It’s also pretty hard to start fire.
Seriously, I recommend to try without looking up the precise details of techniques. Armed with the knowledge of the fire drill.
Re: tasmanians, once again, it is an island. Birds go flightless on islands just because there’s some empty ground animal niche available. We can go complex-tool-less and fire-starting-less on island, too. For the fire starting skill to matter, you got to NEED the fire for survival. In some nearly tropical island, what is the great harm, exactly, in not being able to start the fire? Here you freeze to death in the first winter; there you just eat raw food which is not that much worse anyway. BIG difference in pressure. (also it is altogether possible that they were able to start fire, and it’s just racist claims that they weren’t)
It doesn’t require 16 years of education and then a PhD to master making spears or fire, especially when there’s not a whole lot else to do; even if there were no ceiling, that still doesn’t justify the extremely high calorie and protein consumption of a top-notch brain.
There’s no point in me looking it up; I was a Boy Scout, I knew how to make and use a fire drill.
It’s not really a tropical paradise either.
Winter night temperatures are still way above freezing, though.
Which is why even the highlands don’t receive snow, is that right...
Something did justify the huge brains, somewhat bigger than we have now, and bigger in relation to bodies too. And it sure wasn’t the PhDs.
Very sophisticated society has taught you how to make and use a fire drill, using a process well developed to make a person able to use a fire drill. Did you make it from 100% natural materials you picked up in the forest? What is the range of humidity at which you can start fire? How well you can improvise if something you want to use isn’t available?
Heh, it goes down to −30 Celsius where I live, so i may tend to call stuff tropical even if its kind of cold. The ~0 Celsius weather is not too bad without fire. Even at −30 many animals live just fine without fire.
edit: plus from what i’ve read i’m not even sure they didn’t have fire, in the first place.
You can’t just go around dispelling advantages of big brains without providing any alternative explanation why big brains evolved.
I never said they didn’t have fire; please read what I wrote.
Of course I can.
And besides, it’s a very simple story: if big brains improve individual reproductive fitness by enabling innovations, then there need to be innovations. Evolution can’t act on genotype which is never expressed in phenotype. In Tasmania, not only are there no innovations, there’s actual loss of existing innovations. If you try to argue that the population base was too small, then that’s even more damning: what kind of innovation-supporting gene can be selected for by Evolution when thousands of aborigines over many generations all fail to produce anything? Even if one aborigine did, how does that make up for thousands of his relatives/ancestors burning huge amounts of calories and protein on the innovation-capacity only one of them benefited from?
Combined with the observations about innovating being a public good (and group selection being rare to non-existent), this is pretty convincing evidence that big brains were not selected for their innovation, but for something else—the Machiavellian brain hypothesis seems like a good one.
What’s this with Tasmanians? Did they become a race of super-humans without innovating there and made it obvious that it is not the inventions that drive the evolution towards greater intelligence? Or what?
They all died out, remember? Here’s your reproductive fitness.
Seriously, you’re disproving the evolution of flight by referring to Dodo.
They had a bit of help with that: http://en.wikipedia.org/wiki/Black_War
Only if you want to appeal to group selection. Otherwise, this demonstrate the point: even with the total group shrinking and ever more reproductive fitness possible, innovations still did not materialize and still did not give any individuals fitness.
What more evidence could one possibly ask for?
Some argument that is not equally applicable to reproductive uselessness of flight, based on Dodo. I don’t see yet anything that you said about intelligence and invention and Tasmanians, which wouldn’t be equally applicable to wings and flight and Dodo.
The flight may fail to materialize for a zillion of reasons that have nothing to do with it’s usefulness, or possibility of achieving flight using wings. Ditto for the innovation.
Flight is not even comparable. Flight is incrementally useful, for gliding or flying occasionally to full life airborne. It is directly useful, and all benefits are internalized—I can’t watch you fly and then somehow instantly gain the ability to fly myself; flight is obviously not a public good, and that alone disqualifies it as a comparison.
The point is that even the birds give up the flight on islands despite as you too understand it being so advantageous and internalized and such.
That makes entirely void by counter example your logic chain that if animal (humans) gave up innovation on island (Tasmania), then the innovation must not be very reproductively advantageous in general.
Because regardless of whenever something is or isn’t reproductively advantageous on mainland, it can be given up on islands. Islands have empty niches. Bird gets there, bird may fill a niche usually filled by mammal. Human can get there, and fill a niche of a small bear.
If you want to argue that innovation is not selected for sufficiently because it’s a public good or not incrementally useful or something (I disagree), then do so without invoking Tasmanians as support (and I won’t refer to Dodo).
Continue that line of thought. Why were the birds able to give up their wings?
Because no predators.
Is that true for Tasmanians? Was it a socialist paradise, was it somehow homo homini lupus non est? Was there no pressure for innovation among the groups?
I deny the legitimacy of the comparison; it is as dead and useful as a dodo.
The very (alleged) fact that Tasmanians have lost their technology, yet other groups did not, got to be a fairly good indication that Tasmanians were under less pressure to keep it than other groups. The people that came to far north back during ice age, if they lose their technology there, they promptly die. And on a big continent there’s large number of other people that’ll swiftly get rid of ya if you lose technology.
Also, look at predators: bears, wolf packs, tigers, etc. Vs tasmanian devil and tasmanian ‘tiger’ which sounds scary but is the size of a dog and doesn’t hunt in packs. I’d guess on Mauritius the Dodo coexisted with similar ‘predators’ that can’t eat the Dodo.
Ohh, and the rhetorical questions: hello to the black n white world, where I’d have to prove zero selective pressure in Tasmania. Not interested. It suffices that the pressure is lower and costs aren’t. Humans are very unique animals that evolved under immense external pressure. We barely made it. Homo homini lupus est does not cut it for evolving intelligence, or we’d have the original lupus evolving the intelligence. Every predatory species and it’s granma are pressuring themselves, and not progressing nearly as fast as humans did, under external pressure, having been forced off trees.
Really? Wikipedia links to Cotton (1887) which is handwritten but says:
I did see that mentioned while reading Wikipedia, but I dismissed it. It is a third-hand report from decades (someone told someone who told me who tells you) previously about a method which may—like the Easter Island ‘invention’ of writing—simply have been copying foreigners either directly or indirectly and so even at face value doesn’t establish the claim. I don’t think such a dodgy source is enough to overcome all the reports and circumstances (eg. described cumbersome system of firekeeping seems to be less likely if knowledge of making fire had been retained).
Did the Australian Aborigines undergo similar brain shrinkage? If not, they would be good tests of any particular hypothesis of loss.
Australians split with the rest of us about 30 to 40 ky before the “brains peek”.
And you have little data about “racially sensitive” things, like “brain size of the Aborigines”.
It’s just not politically correct.
This is a feature not a bug of the test.
Unfortunately this is true. There is however some anatomical data available in medical sources that might (however indirectly) add some evidence to our various hypotheses.
The Sentinelese might be a better example, as they’ve not been colonized (which introduces things like “rape, slavery-and-sex-with-slaves, forcible lifestyle changes to conform to something more like the conqueror culture’s modes of subsistence and lifestyle”, any of which might be expected to have an influence on the results). However, just try and find an ethical way to do this research—the Sentinelese are rather serious about maintaining their isolation, and their language is unknown, so informed consent is entirely off the table.
No they wouldn’t. Colonization is a recent phenomena. We aren’t talking about brain shrinkage over the last 200 or 300 years. Australian Aboriginals are old; they’ve been on the continent for tens of thousands of years. If there is any difference in brain size post colonization it is trivial to distinguish.
We will crack the genetics of intelligence and personality in just a few decades, after that DNA extracted from ancient DNA can easily be analysed to give us a good idea of cognitive abilities in those time periods.
I’d be willing to take a bet on that, if we can agree on what would constitute a hit or miss, but your time frame is exceedingly vague—“a few decades” sounds more like a personal hunch than a real estimate.
He’s probably thinking of Hsu and the big Beijing genomics project for IQ, which is already running. It’s hard to imagine, as genome sequencing approaches $1000, that whatever genetic basis exists won’t be pinned down within a few decades. We don’t have to understand why they affect IQ as they do, we just need to infer which ones and the direction of the effect.
That study will probably step right into the trap of ‘got a generator of trillion hypotheses; got a million hypotheses with extreme confidence in them’. It seems people deliberately walk into such traps to produce some data to justify the funding.
The combined effect of what ever genes affect intelligence, is likely to be strongly nonlinear (e.g. a improves iq, b improves iq, a and b decrease iq) . That will be the case even for very simple functional measures, like the speed of running, as clear from understanding of how genes can affect speed of running. There is optimal length to a bone, there’s a lot of genes that affect length of a bone, they must sum to ideal bone length for maximum speed. Repeat for many bones and other parameters.
But as there is no understanding how genes may affect IQ, one has a free pass to model effect on IQ with much simpler model than needed for the running speed, and get away with it, even though its complete absurd. People fail at abstract thought, and IQ is abstract. It’s easy to imagine that it won’t be pinned down, as we’d have only a few billions people to sequence, but much much larger number of pairs and triplets of genes.
Um. You are aware that humans from long-isolated groups can breed and that the majority of traits are polygenic (meaning there are lots of contributing alleles that interact with each other in frequencies that may or may not differ between two populations)? The range for many such possible traits in a human is wider than binary for polygenic traits but its edges are defined by a function of the average edges of the parents’ inherited range (and so on), meaning that if you have two groups with very distinct frequencies and you mix ’em, the results will not be representative of the frequencies of either root source group, and in cases of colonization, that means interbreeding throws off the curves.
You’ve just promted me to respond despite my awoval otherwise. To respond to your question of course I’m aware. I am talking about the huge amounts of genetic information that can be recovered from admixed individuals and even fossils.
Pure speculation, based on the misfiring heuristic that since stone age Europeans where not building cathedrals and where not writing up religious texts they might not have been that religious.
Differences between the average brain sizes of currently existing populations are comparable.
You don’t need to build a cathedral. Mass ritual murder grave suffices.
What is your point exactly? Brain volume correlates with IQ.
Well sure but the absence of mass ritual murder graves from Medieval Europe is a poor indicator of lack of religious craziness. As it is for Stone Age Europe.
Modern humans populations don’t seem that different in their potential for religious craziness. This suggest other possible factors must be at play here. Even differences in intelligence are apparently small enough to be something we don’t agree about despite differences of brain volume between some populations being in the realm of 100+ cc. But presuming there are in fact differences in intelligence and these can be measured sufficiently with IQ as a proxy, it needs to be pointed out that Inuit’s have I think the largest brains of any ethnic group, yet don’t have the highest IQs (though their IQs are higher than the Native American average).
It does. I think it is a 0.4 correlation. However sometimes statistical differences make such comparisons misleading, since obviously female brains are on average smaller than male brains, yet the general consus seems to be that there are no differences in mean IQ and no differences in general average levels of cognitive ability.
I don’t like the data from comparison between genders or between races. We have very strong biases on such topics. Not so long ago one would say that obviously the blacks and the women are much dumber. Very strong real world consequences too, strong inclination for beliefs in beliefs.
With regards to modern human potential for religious craziness, once again there’s very strong inclination to believe its not related to race, unless proven so beyond all doubt. It’d be more illuminating to do study on just the white males or just the white females, then there’s less potential for bias, and less noise too.
It is however pretty accurate data. One dosen’t get a rationalist pass for simply “disliking” it. MRI scans basically match weight of brains after autopsy match measurements of volume in skulls. Reports of bias systematically corrupting even such simple measurements have been greatly exaggerated.
My point with invoking the possibility of such differences was that we are faced with the dilemma of either being right and no systematic difference in ability stems from this systematic and comparably large difference in brain size or the resulting systematic difference in ability has been tiny enough to be either tricky to detect or small enough for us to paper over it and pretend it is not there.
Whatever the interpretation this should be pretty directly related Bayesian evidence to the likley effects of recent shrinkage.
The issue is not the brain volume difference data but the IQ testing and all the issues that go along with it. It is such a loaded topic if you start comparing IQs between races.
And I can see how totally rational scientist could opt to mess some with the data or adjust the tests to not find any difference. Hell, I myself personally have declined to answer the race question on some programming contest (which was by the way utterly dominated by whites and asians; yet i don’t want anyone using this data as a prior whenever someone black tries to apply for a job. I asked why they needed race questions, they said that the data is important for their sponsors, for hiring decisions basically, so here you go. They just correlate everything, then they see, ok whites have better median performance, then when evaluating black candidate they use lower ability as a prior).
Furthermore, different races usually go along with different cultural backgrounds, and the cultural backgrounds influence the IQ test results.
The gender issues are even worse.
Anyhow, your claim basically is that we agree on the brain volume differences between races, which is true, and that we don’t equally agree on intelligence. In my opinion that could as well be an artefact due to difficulty of measuring the intelligence. Brain volume is a physical fact, and it isn’t something we can disagree on as long as science works at all. The relative weights the different skills should have on the IQ test, and the degree of advantage given by the test to those raised in particular cultural background (matching the skills to those perceived important by test writer), those are matter of opinion.
Measuring the brain volume difference between races gives indisputable evidence whenever there is, or isn’t, a difference. Measuring the IQ test results, however, is very disputable.
I don’t recall specifically claiming that there are differences in intelligence here. I do however consider it a plausible hypothesis but one that dosen’t trouble me either way since in about three or four decades when the genetics of personality and intelligence are cracked we will have our final answer. I didn’t wish to open a debate on this in this thread, otherwise I would have opened with more than a one line summary of some craniometric data. The reason I mentioned it at all is that I don’t think one shouldn’t discard relevant information needlessly.
If in one’s estimation there probably aren’t any differences in intelligence update on your model of shrinkage accordingly to this data. If in your estimation there probably are difference in intelligence you should also update your model of shrinkage accordingly.
There really shouldn’t be much of a dilemma here. Of course one’s beliefs about shrinkage naturally will propagate in the other direction. But if you start walling off information that could potentially cause one to update in one way or the other on modern variance of ability, one will eventually need to wall off a lot of science.
I’m a little confused. Are you disagreeing that shrinkage took place, or are you disagreeing that brain volume relates to the ability?
From earlier post:
There’s a perfectly good explanation for having well agreed data that the brain volume varies between populations, yet not having well agreed data that intelligence or other functionality varies between populations: it is straightforwardly true that the variation in intelligence is both dramatically easier to paper over AND we’d be more inclined to paper it over, than craniometry. Ten percent difference between brain volumes can’t be papered over. Ten percent difference in any intelligent function easily can.
Basically, the data we have on intelligence (or tendency towards religious craziness) across ethnic groups is utter and complete garbage. That is not same thing as having evidence for zero variation.
edit: that is to say:
I do not believe that if there was 10% variation of some function across races or genders, such a difference would be reliably agreed upon.
If you take IQ test of same person twice—or take two different tests—there’s much, much less agreement than if you do craniometry using MRI or between different MRI machines or between different methods of doing craniometry. That is to say, our intelligence-sensor got dramatically larger error than our brain-volume sensor, and the data from intelligence sensor would be judged inconclusive for same degree of difference for which the MRI data would be judged nearly indisputable.
In light of this, lack of agreement on this topic constitutes very poor evidence in favour of zero variation of intelligence or it’s various aspects (such as rejecting crazy nonsense). You only stick with zero variation if zero variation is a simplest hypothesis—but independence of intelligence from volume is not a simple hypothesis, but instead a very very surprising one, with potential to overturn much of our understanding of evolution as the larger heads have significant costs.
However, I entirely agree that if we were better able to measure intelligence, and were better able to agree upon the intelligence and its variation across races, then lack of evidence for variation of intelligence and the like across races in presence of variation of brain volume would constitute significant evidence in favour of independence of intelligence and other related functions from brain volume.
Your hypothesis isn’t worth much until you find a way to test it. Simply reasoning it out doesn’t cut it.
Well, I’d say the notion that it did affect innovation definitely needs testing. The notion that we got dumber in some ways, though, should be simply a default hypothesis.
Would a good way to test it be cracking the genetics of intelligence and then compare modern human DNA with recovered ancient DNA?
Why should it be a default hypothesis?
The hypothesis that decrease in brain size corresponded to some partial loss of function is simplest. The only simpler prior is that brain size is entirely unrelated to functionality.
This is pretty much ruled out by fact that brain size (and ratio of brain size to body size) increased through the evolution up to very recently, implying that larger brains must have had an advantage.
With regards to notion that the decrease in size was compensated for by increase in efficiency of the brain, that’s just some backwards reasoning starting from “we couldn’t possibly have got dumber” and arriving at “we must’ve gotten smarter by increasing efficiency”.
If you try to reason this forwards—why exactly would increase in brain efficiency lead to shrinkage of the brain? It could as well lead to growth, if the more efficient brain pays off better for the extra size. Why would the increase in brain efficiency lead to intelligence-preserving shrinkage, while the change of lifestyle and improvements to the survival due to accumulated knowledge—increase in efficiency of survival if you wish - would not lead to shrinkage as well?
Here is another, just as plausible hypothesis: given that intelligence is determined largely by the amount of grey matter of the neocortex, which is a relatively small part of a mammalian brain, the absolute increase in the grey matter volume would allow for much larger absolute reduction in the brain size without reducing intelligence.
There is nothing inherently “default” about either hypothesis, both require experimental testing just the same. If you privilege one of them, you are committing a cognitive fallacy.
If all you know about two mammals is that they have different brain sizes, then it seems plausible to guess that the one with the larger brain (especially if the brain is larger by mass and as a ratio to body size) has greater overall functionality. This doesn’t seem like a particularly privileged hypothesis, just the baseline observation.
Look at the title: ”...what did we lose?”. It assumes that we lost something, seems like clearly privileging this hypothesis.
Keep in mind that white matter is the wiring that is connecting the gray matter. The glia are the cells that support the neurons. And so on. It doesn’t really make most sense to just assume that you can enlarge gray matter, and shrink any of that, without making it work even worse than with more uniform shrinkage.
See, that’s precisely why hypotheses are not equally plausible. The hypotheses are:
a: recent shrinkage was accompanied with some loss of function of the shrinking organ
and
b: recent shrinkage would have been accompanied with some loss of function of the shrinking organ, BUT there was a hypothetical low hanging fruit that was picked at same time [proceed with making extra hypothetical assumptions about what the low hanging fruit might be].
The latter hypothesis is strictly more complex than former. Probably complex enough that we wouldn’t even have been talking about the latter hypothesis had we not arrived at it via backward reasoning, starting from the notion that we didn’t get dumber.
I don’t think you have looked at the brains, and at evolution, and have said—ohh, it makes the most sense that shrinkage of the [whatever you think is shrinking] and growth of the gray matter, is the way how the intelligence and efficiency would have been increased. I think you picked a notion that we didn’t get dumber, and then thought of the ways how you think things could have went so that we didn’t get dumber.
I just reason forwards. I have the shrinkage, I have the relation between size and function, I have the evolution trying to shrink the brain without loss of function for millions years before that timespan, yet the size increased. I reason forwards to loss of function in the recent shrinkage, likely loss of intelligence (which doesn’t bother me as I don’t believe evolution uniformly leads to things we call better).
I think humans aren’t that special in this regard. There are plenty of other examples of domesticated species having smaller brains (Canis lupus familiaris for starters). And yes humans are animals and it would be pretty hard to argue that we aren’t in fact domesticated. :)
If I had to guess I would say that our sense of smell and the part of the brain dedicated to making sense of that data may have decreased significantly precisely because of our domestication of dogs.
Going off some of the writing of anthropologist Peter Frost. I think a good case can be made that in this case:
This seems like a good candidate for brain shrinkage for various reasons. For starters it seems population densities where much higher 20 000 years ago than 200 000 years ago.
Larger population > More brains to store specialized information
Larger population > Economies of scale > Value of specialization rises
Then there is the whole matter of the invention of writing and the formation of hereditary classes preforming different functions.
What kind of information one may store back then, which would result in reproductive advantage? If you are storing more detailed map, you need better path-finding to take advantage of more detailed map; if you store more details of your life, you need to do more statistics to find useful correlations; etc. Extra information needs extra processing.
Today, memorizing declarative ready-to-use facts—prepared by other people—can be very useful—yet they still require a lot of processing so that real world events would bring them to attention. Perhaps less when you have ready-to-use facts and methods to solve the problems prepared for you by another person, who identifies what knowledge you may use. That person however has to be able to match the real world problem to the solution he was taught.
Up voted for taking evolution seriously when it tells us that it simply wants to maximize fitness and dosen’t care about what we like.
I think you are right on our biases regarding this.
Hypothesis I just made up:
Drops in violence and changes in the kind of violence (yay arrows!) in the past 20 000 years have reduced the need for cognitive back ups as well as robust skulls since brain trauma is less common. Our ancestors may have had bigger brains but not have been much or any smarter because they literally got hit on the head more often.
The survivable brain trauma is a product of our adults play-fighting like kittens. Real violence using stones and sticks got larger variance of damage and fewer of the cases would fall into brain-damaged-survivor range.
Picture seriously huge people, built like athletes, fighting not with gloves on their hands but stones in their hands (and stones on sticks). There won’t be many knock-outs where the knocked out party ever gets up again.
Why didn’t Neanderthals evolve it then? Larger brain volume, but musculature sufficient to make a fist a deadly weapon. They could stave in each other’s skulls with a punch.
Evolution doesn’t work that way. The fact an option is available doesn’t mean they will evolve for it unless there is such strong selection pressure to do so it outweighs other factors.
The average size has been going down but the variation has also increased a lot (probably because humans can use culture to stratify by cognitive/physical phenotype). Lord Byron’s skull was 2200g (which is downright unwieldy) and he was neurologically atypical. His daughter was more stable (the second X chromosome can offset deleterious stuff in the patrilineal one), but also wrote the first computer program in 1842. There is probably a correlation:
Family History of Psychiatric Disorders Shapes Intellectual Interests (Jan 2012)
Evolution, brain size, and the national IQ of peoples around 3000 years B.C (2010)
The neuroscience of human intelligence differences (2010)
This could also partly explain the Fermi paradox. May be difficult not to de-evolve too early, for a technological civilization to bloom.
Well, Homo Floresiensis went through a similar phase, and the cultural toolkits we see among them are no less-sophisticated for it (and no more—it’s hard to say how directly-relevant brain size is to intelligence, and it’s much harder to discern the impact of intelligence in potential form on paleolithic or pre-sapiens lifestyle.
I have to say I agree with Gregory Cochran’s scepticism of this. Homo Floresiensis had basically Chimp-sized brains. One would need stronger than usual evidence that they did in fact use them, before we can take that as a given. Has it for example been ruled out that the tools found where brought to the cave by say other humans hunting and eating them?
Floresiensis had a total brain volume in the chimp/australopithecus range, yes, but the dorsomedial prefrontal cortex (associated with higher cognition in humans) is about the same size as it is in anatomically-modern homo sapiens. Their habitation sites show all the usual hominin features: fire, bones with cut marks, stone tools of comparable sophistication to contemporary h. sapiens with four times the brain volume—and the prey species associated with the sites, stegodontids, would necessitate cooperative hunts.
The optimist’s explanation is that we’re shedding hardwired macros.
What happened 20,000 years ago to make a large chunk of macros useless?
Our environment and lifestyle started changing, rendering some instincts obsolete. Also possibly we got better at conscious reasoning, so our instincts became less necessary or counterproductive.
A few years ago a friend dropped a soda can, and it developed a small hole, causing soda to hiss out and the can to start writhing around in the grass, propelled by the escaping stream. The two of us leaped back in terror, my heart started pounding, and I had trouble speaking for a moment. It took a bit for me to figure out why we had that reaction...it was much more than being startled. I’m pretty sure we have a hardwired macro that says “hissing cylindrical thing writhing around in the grass” ⇒ “leap away from it, stare at it, get scared” but never bothers to dump the symbol “snake” into our conscious thought-stream. Presumably we used to have a lot more instincts like that, but as the ratio of real hyena encounters to false positives decreased, the hyena macros became liabilities, or not worth the brain mass.
Or we’re getting dumber. I could definitely believe that.
Hmm, our cats are packed with instincts like this. The housecat’s brain is 30 grams source I dunno how much weight we can lose by shedding instincts but instincts don’t take up a lot of brain.
BTW, one thing that really surprises me about cats is how smart they are for the brain size. Our (my and my gf’s cats) a: are loaded with various instincts and reflexes, b: can understand stuff on first try. I have a small spray bottle that I tried to use as minor negative reinforcement to get dog and cats to stop doing annoying stuff. Dog seems negatively reinforced all right.
Cat sees the bottle pointing in his direction first time, looks with curiosity, then keeps on trying to get into food on stove, i spray him, he sort of lazily runs off. From that time on, he sees bottle turning his way, he just knows what the bottle does, he runs away. He understands how this works. Dog isn’t like that, she’s behaving more like getting conditioned over time.
specific brain features don’t necessarily map to well defined categories of abilities.
No, but size correlates fairly strongly with intelligence, in both primates and humans: http://en.wikipedia.org/wiki/Neuroscience_and_intelligence#Brain_size
So the question becomes, why does this size decrease not decrease general intelligence, or if it left general intelligence alone, what capabilities did it affect? (Maybe visual working memory, given chimpanzees’ superior capabilities in that regard.)
Related reading: http://www.gwern.net/Drug%20heuristics#modafinil
Anthropologist John Hawks (quoted in the Discover article) in this video (at the 9:23 mark) shows data on the shrinking human brain over 16000 years. On his display it looks to me like the scatter extrema for today are over twice as large as the decline in the linear regression line. The number of data points from 16000 years ago is not large.
Why? The first thing I checked has one anthropologist speculating cannibalism might have occurred during the paleolithic for religious reasons, and on the whole doesn’t look very encouraging.
The real argument against cannibalism seems to be easy transmission of infection, not held back by species boundary. If this risk is comparatively sufficiently low, I’d say not eating your fellow humans who died anyway when the food is scarce is a failure mode (famine seems to be convincing enough, and probably occurred often in the prehistoric past).
Excarnation of bodies seems to have been common in some paleolithic populations; it’s unknown whether cannibalism was involved (ritual flensing or excarnation of dead bodies has precedents in other human cultures that don’t habitually practice cannibalism) but it certainly could have been. Mortuary cannibalism is one of the more widespread exceptions—many cultures have or once had mostly-symbolic forms of it (some forms don’t closely resemble modern flesh-eating—Yanomamo consumption of ground bones and ashes as a funerary gesture, for example), and it may also have emerged as a means of predator regulation—don’t leave around bodies that could attract something big and nasty.
A further quote from the same paragraph, emphasis mine:
Just for kicks, I might also assume the (contrarian?) position that cannibalism is by no means unconditionally “really insane,” which seems to be what you’re holding it out as an example of. Sure, it has its (ups and) downs, but I’m not on board for really insane. Killing someone à la Mayan human sacrifice seems to me crazier and more harmful than eating someone’s body as a burial rite at a time when food may well be scarce.
That said, I agree with your thrust; namely, that we have no good reason to believe the paleolithic folks were anyhow significantly smarter or more moral than us.
Depending of what one’s opinion of violence is there may be god reason to think they where significantly worse. Guess what is the most common cause of death among males in hunter gather societies?
Violent death at the hands of another man.
Also there is the general reason to think we are more moral according to our standards than they where, because they where probably trying to live up to a different set of standards than we are.
Actually, causes and rates of mortality for hunter-gatherers vary widely. What you say is true for, say, the Hiwi of Venezuala but not for the !Kung. For some groups, social mortality (cannibalism, war, etc) is high. For others disease is the primary cause of death. Malnutrition is rare, but accidental/occupational deaths are a primary cause for some groups.
According to the data presented by Steven Pinker In all such groups murder rates are vastly higher than in modern developed countries. Though you are right it is not always the number one cause of death.
Stephen Pinker’s selected examples weren’t actually foragers. See here: http://www.psychologytoday.com/blog/sex-dawn/201103/steven-pinkers-stinker-the-origins-war
“Low-tech” and “forager” aren’t the same thing. The Yanomamo aren’t hunter-gatherers. It’s not splitting hairs—this distinction makes a huge difference.
That’s interesting, this reduces my opinion of Pinker’s argument quite a bit. But do we have good data on any group that supposedly has lower murder rates than modern developed countries?
Here’s 25. http://www.peacefulsocieties.org/index.html
Speculating is the key word.
In a harsh environment where humans barely survive, ritual cannibalism would stay just long enough until someone’s protein mis-folded and the stupid practice got the well deserved handicap. You need some sort of tropical paradise isolated from competition to sustain Kuru-afflicted population for any time.
There are plenty of highly-competitive, agricultural civilizations in the tropics.
From the article:
A strong claim if true.
I found this book on google scholar and the parts of it I read supported this claim more than refuted it but were not so definitive and absolute.
Toward the end of the article, they give their theory—that aggressive tendencies were bread out when population density increased. The scenario they describe, is of people getting together to kill off the big hulking brute in their midst.
We became a domesticated species, and like other domesticated species, domestication came with a decrease in brain size.
They note that brain size has been increasing for the last 200 years, but attribute that to increasing nutrition.
I don’t see how the theory that aggressive tendencies were bred out would undermine in any way the hypothesis that intelligence has decreased along with brain size. If we simply bred to be more juvenile as a quick fix for the aggression, that would cause a drop in intelligence. Also I don’t see the data on correlation between brain volume and aggression.
As mentioned the environment plays a large part. My main point is, a more robust phenotype may have been selected for in harsher climates—thicker bones, larger skulls, larger brains. An example are Neanderthals—they became cold adapted, and therefore had a ‘robust’ phenotype. Robust hominins often have thickset skeletons and large heads—and therefore somewhat larger brains as a consequence.
The actual average size of the Neanderthal brain—was not significantly greater than modern humans. Also the Neanderthals had a different shaped skull—and a different version of a hominin brain. While the brain itself does not fossilize—endocasts can be taken from the interior of the skull.
This has been done by the Max Planck Institute—and the endocasts do not match our brain.
Additional research by the Max Planck Institute supports the thesis that the Neanderthal FOXP2 has undergone the same two amino acid changes as us—therefore may have some manner of complex speech??? Humans are not directly descended from the Neanderthal: they are a eurasian production—whereas we are african.
The common ancestor is taken to be Homo heildelbergensis—which was a large brained Hominin—in both African and Eurasian versions.
In all 3 cases—Heidelbergensis—Neanderthal—Homo sapiens—the Genomes will be very close.
Unfortuately none of the present Homo Heidelbergensis fossils are in good enough to be tested. The same goes for Homo erectus.
Only at birth. They grew bigger later in life.
http://newswatch.nationalgeographic.com/2008/09/09/neanderthal/?q=/2008/09/neanderthal.html
That sounds probably-correct.
Perhaps look into self domestication and the recent findings about bonobo self domestication.
Suppose that there were mutations which improved brain efficiency, but had other unfortunate side effects—these would be adaptive above a certain brain size threshold. We shouldn’t of course presume that this was the case, but it’s not implausible either.
As human population densities increased and complex societies formed, selection pressure for social skills increased, and social skills became more relevant than intelligence. Larger brains usually have fewer long-range connections but more local connections, and long-range connections enable the rapid processing required for socialising. People with autism tend to have larger brains than those without and females tend to have smaller brains than males, so an inverse correlation between brain size and social skills would not surprise me.
Hmm. If it’s been going on for 20,000 years, then we have groups of humans living in something like ancestral conditions who’ve been isolated that long. The Sentinelese come to mind (~30,000 years of isolation from the rest of humanity). I can’t offhand think of any ethical way to check this, though. Some isolated peoples in New Guinea might also qualify, but a surprising number of them are farmers and have been for a long time. Regardless, if you checked the average brain volume of people from this group (who haven’t been effected by agriculture, and may not have the technology to make fire, although it’s also conceivable that such a thing could be lost and then regained later) you’d possibly have some idea of whether or not lifestyle changes in the last 10,000 years were a primary factor.
Such groups are also in the most marginal territories, that we haven’t pushed them out of, like the !Kung. Any observed shrinkage might be environmental (eg. nutritional) compared to the old skulls we are looking at, from richer and more normal temperate areas.
I’d bet against that. Civilizations seem to like gods.
Too bad about the timing; if it were within the last 4000 years, then one could argue it’s evidence for bicameralism.
This isn’t that much actually differences in brain sizes between existing ethnic groups are comparable.
Could you clarify for me what this means, exactly? I mean the bit in parentheses in particular; I’ve heard the phrase “god-shaped hole” before but I’m not sure what relevance it has to the topic at hand. Are you postulating a claim that if we were smarter by the brain volume of a tennis ball, we would be more aware of God?
If the shrinking brain volume has been confirmed, what about, say, the amount of folding in the cerebral cortex? Wikipedia says that that area of the brain seems to be responsible for a lot of the stuff we associate with intelligence.
Re: the bit about paleolithic humans not doing insane religious stuff: I think the really kooky stuff stems from oversized communities more than the intelligence difference between us and our ancestors. Yes, the brain architecture is what makes any of it possible in the first place, but I see no real reason to think that our paleolithic friends would have done any better in our modern, decidedly non-ancestral environment.
He was claiming the opposite: if we were more intelligent, then we would not have use for a God hypothesis.
Not even that… the God hypothesis aside, religions are full of things that make absolutely zero sense.
Regardless of whenever there is or isn’t God (or Gods), it is pretty insane to e.g. kill a blood relative for good luck. That kind of thing. Not even the God hypothesis. The extreme gullibility. If you are being bombarded by extremely insane propaganda all your life, you will be affected no matter how smart you are. But you don’t need to be so much affected as to preserve this insanity over the generations or evolve this insanity to even greater levels. If each next generation is even a little bit less religious, the religion just decays.
Is this result (brains are shrinking) really well-established? My first impulse is to defy the data...
It is.
You defy the data when you got some theory that is of higher confidence. The “we haven’t gotten dumber” is not a proper theory, it’s just hanging in the air without having been first arrived at from some data.
Please look around you. Does it look like we have got dumber in the last 20,000 years? I’d say this is tons of data. It may be hard to estimate in Bayesian terms, but certainly not less than +100 db of evidence against the alternative.
What I see when I look around is largely the product of millenia of cumulative invention and discovery.
So we got dumber, but more inventive, more creative, and more communicative?
It’s conceivable that most people need less mental resources because a lot of thinking has been outsourced to the infrastructure.
It’s certainly takes less neurological resources to walk on smooth pavement than rough ground.
Could less interpersonal violence mean less need for some mental capacities?
It’s certainly lessened the need to, for example, be able to see a punch coming and avoid it…
I wonder how much driving cars affects the brain? There does seem to be evidence that the brain’s structure changes depending on the demands that are placed on it, and driving a car is a rather unusual cognitive task compared to what people would have been doing in the Paleolithic...
Not just seeing a punch coming in the literal sense, but making strategic choices about odds and allies.
The problem for me with this and other proposed hypotheses is that similar or better ones would equally well explain the reverse effect. So I am still confused after hearing them.
Thus my original question: is the data really well established? Is it confirmed replicated findings of lots of dug out skulls all over the world, or?
It’s very hard to tell. Clearly having infrastructure isn’t direct evidence of present intelligence; the rate of innovation’s probably related, but it’s also affected by communications, culture, and scale effects, and then we’ve got the Flynn effect confounding things recently. This gets even harder when we talk about culture 20,000 years ago; that’s before writing or large-scale societies, so ideas would propagate much more slowly and would be more prone to dying out under suboptimal conditions.
If we had a good idea of what might be driving the changes in brain size, we could look at present-day or at least recent cultures subject to similar forces and see what the deltas there are—although that opens up the usual cross-cultural psychometric can of worms. But we don’t have anything I’d consider compelling, and we certainly don’t have any Paleolithic tribesmen handy that we can sit down with Raven’s progressive matrices, so that leaves us with various proxies for intelligence—of which braincase size is one, at around .4 significance if I remember right.