We know the brain has been evolving in human populations quite recently," said paleoanthropologist John Hawks at the University of Wisconsin at Madison.
Surprisingly, based on skull measurements, the human brain appears to have been shrinking over the last 5,000 or so years.
"When it comes to recent evolutionary changes, we currently maybe have the least specific details with regard the brain, but we do know from archaeological data that pretty much everywhere we can measure - Europe, China, South Africa, Australia - that brains have shrunk about 150 cubic centimeters, off a mean of about 1,350. That's roughly 10 percent," Hawks said.
"As to why is it shrinking, perhaps in big societies, as opposed to hunter-gatherer lifestyles, we can rely on other people for more things, can specialize our behavior to a greater extent, and maybe not need our brains as much," he added. (source)
It’s usually assumed that humans have steadily increased in intellectual capacity. But what if this trend reversed with the advent of civilization? As societies grow more complex, perhaps the average human has not had to know so much. He or she can ‘delegate’ tasks (not that such delegation is always voluntary). Perhaps civilization has made us dumber, not smarter.
Yes, the ‘great civilizations’ have made major contributions to the arts and sciences, typically through upper-class patronage of creative individuals—who otherwise would have to worry about their next meal. The down side, however, is that this emancipation of creativity requires a much larger number of helots. The latter also specialize in their own way—in doing the grunt work that others consider beneath them.
In the ancient world, intellectual life—the debating, pondering, and creating of new ideas—was confined to a small powerless minority, too few in number to generate the critical mass that makes intellectual ferment possible. There were no conferences, no academic journals, and no scientific associations. For the most part, there were only isolated individuals who felt estranged from the world around them. The more renowned ones had disciples in their entourage. But that was it.
This situation contrasts with that of Western Europe and then North America from the 17th century to the 20th. That intellectual ferment was broad-based. It took place within a large swath of the population that could understand the ideas being generated, and that could argue the pros and cons. It was this democratization of intellectual activity that made the West so exceptional.
I’m increasingly convinced that extreme social stratification—i.e., the creation of a small class of intellectuals and a much larger helot class—is inimical to true scientific progress. The intellectuals are too few in number, and too dependent on the system, to make any real contribution.
16 comments:
I've seen this article doing the rounds. I'm not sure how the trend can be parallel in Australia, presumably amongst Australian Aborigines or else you would wonder why it was even mentioned, and still be taken as evidence that a switch to civilization or agriculture from hunter gathering has any causal role in brain size changes.
There would be a class of manual workers over the helots, even if the jobs were semi-skilled those making a success of their occupation would surely tend to be intelligent. In most periods civilization must have selected against this kind of success bringing commensurate reproductive success I suppose.
The cottage industry semi-skilled family labour teams may have multiplied to increase average IQ in Western society but their occupation hardly required or selected for a creative thinking intellect.
'True scientific progress' requires a critical mass of the 'IQ' intelligent in intellectual ferment yes, but it is contigent on something else. Those who - in addition to being intelligent - can come up with genuinely creative thinking.
The last chapter of John Mannings book is quite interesting about the basis of creativity although nothing is really spelt out.
Albert Einstein and James Watson both had sons who were schizophrenic...
I think starvation selects against big brains because they consume so much energi.
How do you account for the poor academic and psychometric performance of peoples who were recently hunter gatherers who have tried to integrate into modern societies? Looking at the psychometric and brain size data from around the world, two patterns seem to emerge: 1) For hunter-gatherers, and people in general, the farther north one goes, brain size and psychometric g tend to increase, and visuospatial skills seem to increase even more strongly. 2) Populations with a long history of hierarchical, usually literate agricultural civilizations seem to have higher g than populations without such deep histories in this kind of lifestyle and also tend to do better at tests measuring g at a given average brain size than hunter gatherers or peoples with shorter histories of complex agricultural civilizations.
Just a guess, but recent neuroimagining studies are establishing a link not just between g and the amount of gray (neurons) and white (axons) matter in certain brain regions (particularly the prefrontal lobes and parietal lobes – I’ve often wondered about the latter and the trend towards brachycephalization in Eurasia in historical times), but also between g and the quality of the white matter and between g and the efficiency of glucose metabolism in the brain. Perhaps Maltusian food scarcity in large complex societies has selected for more efficient, smaller brains that use less energy and work at least as well as those of our Paleolithic ancestors? That may account for the patterns noted above.
The modern, 20th/21st Century welfare state does seem to create dysgenic selection pressures on a society, but, based on the work of Gregory Clarke, I am doubtful that this would apply to earlier periods where survival of the richest (and presumably the brightest and most patient) seems to have been the rule.
Larger brains present a problem. They are expensive developmentally, during birth, and during life (because of their energetic needs).
Perhaps we are seeing selection for more efficient brains. We know from psychometric research that the more intelligent tend to make more efficient use of energy in their brains.
Anon,
Yes, I agree. As far as I know, the Australian Aborigines have not undergone any social complexifiction over the past 5,000 years. I'm also not sure whether any changes among them would be evolution in situ. It's more or less accepted that there were several waves of migration into Australia.
John Hawks doesn't seem to have published anything on this yet (he's probably still gestating this study), so I'll have to sit on my hands until I can get a better look at his data.
Tod,
Like you, I used to feel that the scientific revolution that began in the 17th century was contingent on some extraneous factor (discovery of the New World, improvements in trade, rise of Protestantism, separation of church and state, etc.). Increasingly, I'm moving away from that position. I suspect that these 'enabling' factors themselves flowed from a common cause, i.e., a steady rise in mean IQ and the advent of a critical mass of people with IQs over 120.
Once you get that critical mass, the synergy takes off: people form academic societies, they read each other's papers, they pool their efforts to resolve common questions, etc. Without a critical mass, you get what the ancient world had: isolated thinkers with small groups of disciples (if they're lucky).
Mans,
I disagree. When starvation strikes, the intelligent are often the ones who survive. They are the ones who will store food in the fall, knowing that there won't be enough in late winter.
Anon,
Some hunter-gatherer peoples score well on modern IQ tests (e.g., the Inuit). I also suspect that some of the geographic variation in IQ results from differing abilities to process written text. I'm not saying that text-processing ability accounts for all human variation, but I think it's a factor.
I'm not sure that Clarke's model would apply to great civilizations like Greece, Rome, and Islam. For one thing, these civilizations were demographically 'open' -- they were continually importing slaves, servants and mercenaries to fill labor shortages. So there wasn't the same demographic replacement of the lower classes by the upper and middle classes (as happened in England).
Another thing is that individual success in the ancient civilizations was due much more to clientelism and patronage. In England, success tended to be economic (through trade or cottage industry), especially from the 1600s onward.
Since we now have such strong cultural transmission of knowledge and etc, it's possible that we are seeing the elimination of some inbuilt knowledge that required brain space in favor of more generalized learning abilities.
Natural selection is largely replaced by artificial selection in the process of domestication. I suspect that a similar process seen in the domestication of animals, which results in a loss of intelligence among domesticated breeds when compared to their wild counterparts, may be at work in humans who live in large societies as opposed to hunter-gatherer groups. Perhaps it's something at work in the forming of pair bonds which results in a type selection with results similar to that found in the process of domestication.
Wheat and other grains are known to screw mineral metabolism and speed up our bodies' rate of consuming fat soluble vitamins (esp D3 & K2) that are absolutely vital for growing of bone structures.
Guess which people spend least wheat/grains AND have the biggest brains?
Asians.
Smaller skulls mean smaller brains, of course.
Neonomide - There is evidence on the 'benefits' of vitamin D supplementation such as brain lesions.
"Oral vitamin K antagonists are currently the most effective form of stroke-prevention therapy in patients with atrial fibrillation"
I'm wondering, could combining 'vitamin' D and vitamin K produce a synergenic effect on the brain.
While clientelism and patronage were important there would still have been some competition for the sinecures; those with 'people skills' and high intelligence would have been selected for to a certain extent. If patronage - centred societies had a lack of impact on the average IQ over the such a very long period of time the explaination might lie not in a total lack of selection for intelligence; the more intelligent may be affected differently by civilization.
Natural selection in proto-industrial Europe advances the hypothesis that there was a baby boom among the most successful - presumably the most intelligent - cottage industry artisans. This was in order to increase the householder's workforce. For these higher IQ men having a bigger family was a means to an end: bigger profits.
It follows that the more intelligent need an incentive to have bigger families. they always needed an incentive that affected them only to have larger families than the less intelligent. Therefore it might be the essential point in the NSIPIE explaination is being lost in attributing the lack of selection for IQ in the patronage era to an actual lack of success enjoyed by high IQ men. To put it another way the cleverer men could have afforded to bring up a lot of children but in practice they never fathered them because the natural inclination of higher IQ men is to have less children than they can afford.
Up until about 1600 dim men fathered lots and many died, but enough survived to more or less equal the reprductive fitness of the bright so the average IQ did not go up.
While clientelism and patronage were important there would have been some competition for the sinecures; those with 'people skills' and high intelligence would have been selected for to a certain extent. If patronage - centred societies had a lack of impact on the average IQ over the such a very long period of time the explaination might lie not in a total lack of selection for intelligence; the more intelligent may be affected differently by civilization.
Natural selection in proto-industrial Europe advances the hypothesis that there was a baby boom among the most successful - presumably the most intelligent - cottage industry artisans. This was in order to increase the householder's workforce. For these higher IQ men having a bigger family was a means to an end: bigger profits.
It follows that the more intelligent need an incentive to have bigger families. they always needed an incentive that affected them only to have larger families than the less intelligent. Therefore it might be the essential point in the NSIPIE explaination is being lost in attributing the lack of selection for IQ in the patronage era to an actual lack of success enjoyed by high IQ men. To put it another way they could have afforded to bring up a lot of children but they never fathered them because the natural incination of higher IQ men is to have less children than they can afford.
Up until about 1600 dim men fathered lots and many died, but enough survived to more or less equal the reprductive fitness of the bright so the average IQ did not go up.
Domestication reduces brain size in animals, and humans show many signs of being self-domesticated.
I suspect the reduction in brain size goes back at least to the development of agriculture, which AIR was pretty much coterminous with the first urbanisations.
Tod said...
"Neonomide - There is evidence on the 'benefits' of vitamin D supplementation such as brain lesions."
- Obviously the study you are referring is somewhat redundant, not least because the minuscule dose of Vit D that was used and the crappy methods:
"Payne et al was a small, questionnaire-based study that did not measure vitamin D in the blood. People with brain lesions are more likely to be in an institution. Institutionalized people are given more calcium and vitamin D. The amount of vitamin D they reported would barely have made a blip on the vitamin D blood tests I do in my laboratory, so I regard the relationship as implausible because it was not enough to make a difference."
- Reinhold Vieth, Vit D researcher:
http://www.theglobeandmail.com/news/opinions/article794167.ece
I bet that if there was a culprit, it was excess calcium. People get too much calcium anyhow nowadays and too little magnesum, as these work in synergy. Putting it bluntly, Vitamin D supplementation itself does not do anything for calcium absoption unless blood 25(OH)D levels rise too. This is not always the case, especially eith older people. And the 10 µg dose rises 25(OH)D very little. So they used a homeopathic dose really and the study was nothing to write home about.
Tod said...
"Oral vitamin K antagonists are currently the most effective form of stroke-prevention therapy in patients with atrial fibrillation"
- -
"I'm wondering, could combining 'vitamin' D and vitamin K produce a synergenic effect on the brain."
- An excellent question. We know that D3 and K2 have remarkable synergy with themselves and with Vit A as well. I honestly think that a "normal" metabolic milieu should start from paleolithically plausible availability of all these three and some minerals too, like magnesium and iodine. Basically all of those are lacking in most modern diets, bar Vit A. We know that Vit A causes several problems- probably many of them because of deficiency of Vit D.
I would add that Vit K antagonist varfarin (Coumadin) seems to cause atherosclerosis in rats and kidney patients. Even more interestingly, K2 supplementation can _reverse_ varfarin induced severe atheroschlerosis in a couple of months.
I think calcium metabolism is severely screwed in many modern people and that deficiencies and bad ratios of fat-soluble vitamins (and certain minerals) are very important players in the process.
- -
Coming back to the topic, I think that the safest bet so far is to think that since cranial capacity started to shrink like 11% since the upper Paleolithic, each and any optional (and speculative) theory must take the neolithic Agricultural revolution into account.
http://www.nature.com/nature/journal/v387/n6629/abs/387173a0.html
I simply think that the evolutionary rationale for smaller brains does not exist without the food aspect taken seriously.
I must say that I'm quite intrigued Vit D aspect on intelligence. Indigenous peoples near the equator seem to perform lower on IQ tests, yet mothers who eat a lot of fish have more intelligent children - often without correlation with Omega 3.
Vitamin D is a potent neurosteroid that makes elderly people more proficient in several cognitive performance tests - which again plays against to the idea that Vit D would decrease brain functioning.
Confusing, eh?
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