Saturday, August 4, 2012

Too darn hot?


Does higher IQ correlate with colder temperatures? Not among people belonging to the same cultural system, such as the Chinese. (source)

Big brains are costly, not only because of their high energy consumption but also because many genes have to interact to create neural tissue. The bigger and more complex the brain, the more it is vulnerable to accidents at the gene level, like random mutations.

Mutations happen more often at warmer temperatures. In Drosophila, an increase of 10ÂșC will double or triple the mutation rate. Tight underwear has probably done more to harm the human genome than fallout from nuclear testing (Sutton, 1975, p. 318).

Drawing on these two points, Greg Cochran is now suggesting that large human brains are a precarious outcome of evolution (here and here). However strong the natural selection may be for a bigger brain, the mutation rate is pushing back in the opposite direction. Beyond a certain size, big brains are possible only where the mutation rate is relatively low—in cooler regions at higher latitudes.

This is a seductive way of explaining why brain size correlates with latitude. And, yes, such a correlation does exist. So thought most 19th-century physical anthropologists, notably Samuel George Morton, but Stephen J. Gould (1978) concluded otherwise after a reanalysis of Morton’s data that became the centerpiece of his book The Mismeasure of Man. A team of physical anthropologists has since located and remeasured Morton’s skulls. Their conclusion? The original measurements had few errors, and the errors were distributed randomly. There was, in fact, a non-significant tendency by Morton to overestimate African skull size (Lewis et al., 2011).

Brain size and latitude also seem to correlate among ancestral hominids from A. Afarensis to H. sapiens (Henneberg & Miguel, 2004). The correlation remains even if time period is controlled. It thus cannot be due to the overall rise in cranial capacity over time and the parallel expansion of ancestral hominids into higher latitudes.

Is this correlation adequately explained by the ‘Too Darn Hot’ theory? The main supporting evidence is the finding that ‘loss of function’ mutations are much more common in sub-Saharan Africans than in other humans (MacArthur & Tyler-Smith, 2010; Tennessen et al., 2012). Natural selection seems to have more trouble weeding them out in the tropics than elsewhere.

But do these mutations need to be weeded out? Are they in fact deleterious? Some authors think so. Most don’t, including the ones of a study that Greg cites:

[…] the implicit assumption that LOF variants (and indeed other changes predicted to be damaging to the protein) are necessarily deleterious to human health is a dangerous one, especially when such an assumption is used to infer disease causality for a novel variant. In fact, the studies reviewed above demonstrate that healthy humans carry many dozens of LOF variants, most of which have little or no effect on health (at least in the heterozygous state). (MacArthur & Tyler-Smith, 2010)

In general, these mutations seem to involve genes of very low selective value, so they could very well hang around indefinitely if natural selection against them is weak enough and if the population is large enough.

Here we come to the usual explanation for Africa’s large number of ‘loss of function’ mutations. There are so many of them because Africans have largely stayed put in the same place with the same population base. In contrast, non-Africans are descended from small founder groups that took only a small portion of this junk variability on their way out of Africa:

The gene-diversity results presented here are consistent with one another and with those of many previous studies in showing higher levels of diversity in African populations than in non-African populations […] A higher level of African diversity supports the hypothesis that modern humans first arose in Africa and then colonized other parts of the world (Stoneking 1993), but genetic diversity is related not just to a population’s “age” but also to demographic events in a population’s history, such as bottlenecks and effective population size. (Jorde et al., 2000)


Alternate theories


Do we have other theories for latitudinal variation in brain size? To date, there seem to be three:

Need to reduce heat loss at higher latitudes


According to Beals, Smith & Dodd (1984), heads have grown larger at higher latitudes as a way to reduce heat loss. An object will lose less heat if it has a high ratio of volume to surface area. Natural selection has thus favored more globular heads at higher latitudes. The increase in brain size is thus incidental.

This explanation was challenged in the comments section of the above paper. Iwatoro Morimoto pointed out that "in recent centuries, brachycranic skulls show a considerable increase in frequency in Eurasian populations, including the Japanese." Since mean temperatures have changed little in recent centuries, there must have been another factor at work.

Another commenter, Erik Trinkaus, similarly pointed out that Neanderthal cranial capacity was no bigger during glacial periods than during interglacials. The same was true for early modern humans. For populations already established at northern latitudes, cranial capacity shows no evidence of rising and falling with mean temperature.

Finally, if the increase in brain size was driven by the need for a more globular head, that goal can be met by filling the extra head space with non-neural tissue, like bone or cartilage. Neural tissue has a high maintenance cost. Why maintain something at great expense if you don’t really need it?

Increase in visual cortex at higher latitudes


Pearce and Dunbar (2011) argue that bigger brains are an adaptation to lower levels of ambient light. Specifically, dimmer light requires larger eyes, which in turn require larger visual cortices in the brain. Using 73 adult crania from populations located at different latitudes, the two authors found that both eyeball size and brain size correlate positively with latitude. The correlation was stronger with eyeball size, an indication that this factor was driving the increase in brain size.

How credible is this explanation? First, visual cortex size was not directly measured. The authors inferred that this brain area was responsible for the increase in total cranial capacity. Of course they couldn’t have done otherwise. They were measuring skulls, not intact brains.

To date, the best map of human variation in brain size is by Beals et al. (1984). If dimness of light is the main determinant, brain size should be highest in northwestern Europe, northern British Columbia, the Alaskan panhandle, and western Greenland. These regions combine high latitudes with generally overcast skies. Yet they are not the regions where humans have the biggest brains. Instead, brains are biggest among humans from the northern fringe of Arctic Asia and from northeastern Arctic Canada. These regions are, if anything, less overcast than average. They often have high levels of ambient light because of reflection from snow and ice.

Increase in cognitive demands at higher latitudes


Finally, brain size may have increased at higher latitudes because of an increase in cognitive tasks, specifically foresight. As ancestral humans spread out of the tropics and into latitudes with a predictable summer/winter cycle, it became much more advantageous to simulate the future consequences of present actions.

This point is discussed by Hoffecker (2002, p. 135). Among early modern humans, tools and weapons were more complex at arctic latitudes than at tropical latitudes. “Technological complexity in colder environments seems to reflect the need for greater foraging efficiency in settings where many resources are available only for limited periods of time.” Arctic humans planned ahead to cope with resource fluctuations and high mobility requirements, such as by developing untended devices (e.g., traps and snares) and means of food storage.

Colder environments imposed even higher cognitive demands when hunting and gathering gave way to agriculture. Food had to be grown not only for present needs but also for the next cold season. As late as the 18th century, farm families often faced starvation in early spring—when their winter provisions had run out and their spring crop had not yet come in.

The yearly cycle and the need to plan ahead thus preadapted early non-tropical humans for later cultural developments, such as invention of writing and bookkeeping, complexification of social relations, creation of towns and cities, systems of military defense, roads and highways, etc. At that point, cognitive demands were no longer driven by the yearly cycle, at least not primarily. They were now being driven by an increasingly complex cultural environment—what we call ‘civilization.’

Conclusion


How does the ‘Too Darn Hot’ theory stack up against these alternate theories? The main contender seems to be the last one, i.e., the increase in cognitive demands at higher latitudes. According to that theory, the yearly cycle has given way to gene-culture co-evolution as the main driving force behind increases in intellectual capacity.

Thus, if people live within the same cultural system and are exposed to similar cognitive demands, they should on average have the same intellectual capacity … regardless of the mean temperature of their particular locality.

Conversely, the ‘Too Darn Hot’ theory would predict the existence of a north-south cline in IQ even among people of a similar cultural background, since people at more tropical latitudes should have a higher incidence of deleterious mutations.

China, for example, covers a wide range of latitudes from the sub-Arctic to the tropics. Although the Chinese have occupied this latitudinal range for some 2,500 years, i.e., about 100 generations, their mean IQ doesn’t seem to vary along a north-south cline (see above map).

Perhaps 100 generations isn’t long enough. But what about the Amerindians? They’ve inhabited a full range of latitudes from the Arctic to the equator for some 12 to 15 thousand years. That’s 480 to 600 generations. Is there a difference in mean IQ between the Naskapi of northern Labrador and the Yanomamo of Amazonia? I’d be surprised.

References


Anon. (2011). IQ geography in China, November 19, The Slitty Eye,
http://theslittyeye.wordpress.com/2011/11/19/iq-geography-in-china/

Beals, K.L., C.L. Smith, and S.M. Dodd (1984). Brain size, cranial morphology, climate, and time machines, Current Anthropology, 25, 301–330.

Cochran, G. (2012). Changes in attitudes, West Hunter, July 18
http://westhunt.wordpress.com/2012/07/18/changes-in-attitudes/

Cochran, G. (2012). Too darn hot? West Hunter, July 14
http://westhunt.wordpress.com/2012/07/14/too-darn-hot/

Gould S.J. (1981). The Mismeasure of Man. New York: W. W. Norton and Company.

Gould , S.J. (1978). Morton’s ranking of races by cranial capacity: unconscious manipulation of data may be a scientific norm, Science, 200, 503–509.

Henneberg, M. and C. de Miguel. (2004). Hominins are a single lineage: brain and body size variability does not reflect postulated taxonomic diversity of hominins, Journal of Comparative Human Biology, 55, 21–37

Hoffecker, J.F. (2002). Desolate Landscapes. Ice-Age Settlement in Eastern Europe. New Brunswick: Rutgers University Press.

Jorde, L.B., W.S. Watkins, M.J. Bamshad, M.E. Dixon, C.E. Ricker, M.T. Seielstad, & M.A. Batzer. (2000). The distribution of human genetic diversity: a comparison of mitochondrial, autosomal, and Y-chromosome data, American Journal of Human Genetics, 66, 979–988.

Lewis, J.E., D. DeGusta, M.R. Meyer, J.M. Monge, A.E. Mann, R.L. Holloway. (2011). The Mismeasure of Science: Stephen Jay Gould versus Samuel George Morton on Skulls and Bias, PLoS Biology, 9(6) e1001071

MacArthur, D.G., & C. Tyler-Smith. (2010). Loss-of-function variants in the genomes of healthy humans, Human Molecular Genetics, 19, R125-R130.

Pearce, E. and R. Dunbar. (2011). Latitudinal variation in light levels drives human visual system size, Biology Letters, doi: 10.1098/rsbl.2011.0570

Sutton, H.E. (1975). An Introduction to Human Genetics, New York: Holt, Rinehart and Winston.

Tennessen, J.A., A.W. Bigham, T.D. O’Connor, W. Fu, E.E Kenny, et al. (2012). Evolution and functional impact of rare coding variation from deep sequencing of human exomes, Science, 337, 64-69.


23 comments:

Anonymous said...

Whas "what we call civilization" such a non-tropical thing in its early days? think of India and the Mayas. And maybe tropicals, living in more dense, near K conditions didn't really have less of a nead for planning as hunter-gatherers and early agriculturalists: the weather is easy to plan for once you know your gonna have a more or less cold period, followed by a more or less warm one, dealing with other people is the real bitch. As for later days, it once was medically very difficult to have cities in the tropics, especially the Old World ones. And maybe higher mutational load could be partially a response to more germs (though certainly having more mutations must certainly help. But don't forget that, unlike those darn lab flies, we have a greater control over our temperature, and Africans might have used less-and less tight-underwear). At any rate, excperience has taught me to go by what could be Dr. Cochrans motto: have faith in germs.

W.LindsayWheeler said...

Or maybe, "IQ" has nothing to do with Material causes. The Book of Sirach has this to say:
""And all men are from the ground, and Adam was created of earth. In much knowledge the Lord hath divided them, and made their ways diverse. Some of them hath he blessed and exalted, and some of them hath he sanctified, and set near himself: but some of them hath he cursed and brought low, and turned out of their places. As the clay is in the potter's hand, to fashion it at his pleasure: so man is in the hand of him that made him, to render to them as liketh him best." (LXX, Ecclesiasticus 36.10-13)

Maybe they were "made that way". By Design. OHG, heresy! I may have to be banned for that. Just maybe science can not find an answer on why differences because it is spiritual in nature! OMG, another heresy in our skeptic-ladled materialist world.

I always like that quote. It explains alot and don't need no fancy papers to tell me otherwise. It matches what my eyes see and sense.

Anonymous said...

"It matches what my eyes see and sense."

It matches what a lot of people's eyes see and sense(?). That's why it was written down in the first place.

Anonymous said...

Finally, if the increase in brain size was driven by the need for a more globular head, that goal can be met by filling the extra head space with non-neural tissue, like bone or cartilage. Neural tissue has a high maintenance cost. Why maintain something at great expense if you don’t really need it?

This is a cogent objection, but in terms of mechanics, I think it is not the case that it is so easily to select for ever heavier and more robust skulls.

The braincase forms by intramembrous ossification, in response to the expanding brain and driven by it - http://en.wikipedia.org/wiki/Intramembranous_ossification

Craniosynostosis and other malformations / variations in the shape of the brain case are instructive here.

e.g. http://en.wikipedia.org/wiki/Craniosynostosis#Primary_microcephaly - Primary microcephaly shows a clinical image of craniosynostosis, but due to a different cause. The primary failure is the absence of growth of the brain, rendering the sutures of the cranial vault useless.[8] As a consequence, the sutures close, presenting a pansynostosis like image Note that the sutures close in response to decreased brain growth.

Similarly note how in craniosynostosis, when one of the sutures closes prematurely, brain growth simply expands in the direction of the other sutures (whether this actually has any issues in terms of development separate from the syndromes which cause craniosynostosis is contentious).

Based on this, I think it's quite viable to suggest that an expansion of the brain combined with downregulation of its activity (thus entailing less wear and tear maintainance and energy usage), as an alternative to increases in bone or cranial blood or cerebrospinal fluid (the latter two off which have horrible consequences for intracranial pressure. And bone (and the rest) don't exactly have a zero maintainance cost either. Not necessarily true, but viable.

Is there a difference in mean IQ between the Naskapi of northern Labrador and the Yanomamo of Amazonia? I’d be surprised.

There is a brain size difference between them though, no?

Sean said...

Brains shrank in the Magdalenian, but this was when there was a need for storing huge amounts of spatial information for navigation during hunting trips across the steppe tundra. Maybe brain organisation became more efficient.

Africans do not seem to be affected in 'Level I,' mentation

I wonder about repeated consanguineous marriage taking out the most deleterious mutations, consanguineous marriage was common in China. And it is still widely practiced across Sub Saharan Africa. Africans' problems in higher intellectual functions is maybe because they were not selected for that, so mutations in that area weren't removed.

What about the effect that polygyny has on the age of fathers? Older men have more mutations.

Combining the effect of many generations of polygyny and consanguineous marriage would mean what for the prevalence of mutations?

Where is the deleterious effect on attributes that were the key to attracting or appropriating women?; (fighting and dancing). I suppose the mutations in the attributes that were the focus of selection could have had the mutations burnt out. Hence whites can't jump.

Beyond Anon said...

My question would be:

Can the hypothesis of higher levels of LoF mutations closer to the tropics simultaneously explain both the higher physicality, on average, of sub-Saharan Africans (as evidenced by their dominance in sports of a certain type) and their lower IQ, on average?

Anonymous said...

I was trolling on wikipedia on Russian Cosmism and came upon this...

http://en.wikipedia.org/wiki/Alexander_Chizhevsky#Sunspots_and_mass_excitability

Anonymous said...

"However strong the natural selection may be for a bigger brain"

I wonder about this. In a modern high-tech world it may seem obvious but for most of human history - given the calorie cost of large brains - i'd have thought the opposite was more likely i.e. selection for the smallest brain you could survive with.

If you think about it although IQ is supposed to predict better performance at any cognitive task *how much* better would a 130 IQ shepherd be compared to an 85 IQ shepherd and would the benefit outweigh the extra cost?

I don't think it would whereas the difference between an 85 IQ engineer and a 130 IQ engineer must be practically infinite?

It seems to me evolution would be more inclined to select for stupidity wherever it was possible to be stupid and survive - especially in a social animal where as long as your IQ distribution meant you'd always have a chief and a witch doctor with a brain they could carry the rest of the group.

So to my mind evolution would only select for bigger brains when it was vital - hence why i agree with the latitude / seasonal theory but i don't see that as inconsistent with the genetic load idea. If you imagine it as two competing forces the tropical forces might have been
- small cheap brain is better
- don't need extra brains
- too hot anyway

whereas at higher latitudes
- small cheap brain is better
- need extra brains
- luckily not too hot

.
"In general, these mutations seem to involve genes of very low selective value"

This ties into the above. What might have low selective value in a valley full of shepherds might be of high selective value in a modern environment.

.
"Although the Chinese have occupied this latitudinal range for some 2,500 years, i.e., about 100 generations, their mean IQ doesn’t seem to vary along a north-south cline (see above map)."

One of the noticeable things about that map is the island of high IQ around Beijing. I expect most people would agree that's probably to do with centuries of high IQ migration to the capital than anything to do with the physical environment.

Given that China has been a unitary state for a long time then if the southerners were downwardly mobile over time due to genetic load then they would have been replaced at the top level by northern imports in a process similar to Greg Clark's views on the English middling class.

Similarly one of the big distinctions in China north vs south is the coast. The trade centres are all along the southern coast with an effect similar to America's two coasts i'd imagine.

If the above is true then the place to look for undistorted north-south IQ distinctions in China would be among the rural and non-elite part of the populations in the land-locked provinces to the west so the northwest compared to the southwest rather than north-south.

.
There's also another possible factor which is that cultures may develop ways of better shedding genetic load e.g. by creating a competitive exam system with winners and losers - assuming the losers have higher average genetic load and winning and losing has reproductive consequences - and once that has been developed they can hit and retain their peak regardless of the latitude.

This could be why the Chinese seem to be immune to nutritional and Flynn type improvements. They hit their peak - in terms of reducing genetic load to a minimum - already.

.
The Native American example seems more viable as a test case to me.

Peter Fros_ said...

Anon,

In ancient times, there were few civilizations in the tropics. Mesoamericans (Aztecs, Toltecs, Mayas, etc.) and the Incas are the main exceptions, and those civilizations were founded by Amerindians who had lived in the Arctic only a few thousand years earlier.

The same seems to hold true for the subtropical civilizations of South Asia and the Middle East. The language families that now dominate not only Europe but also North Africa, the Middle East, and South Asia seem to originate in northern Eurasia. It may be that northern Eurasians were "preadapted" for the niches that opened up with the development of civilization. They were thus able to displace earlier peoples who were nonetheless better adapted climatically.

Lindsay Wheeler,

It was commonly believed in biblical times that God could curse not only individuals but also entire communities and their descendants. This belief is also common among traditional Inuit. If an individual acts in a wrong way, his/her offspring will be viewed with suspicion, i.e., as being likely to act in the same wrong way.

Anon,

But if the aim is to have a more globular head, couldn't this be done by having thicker layers of tissue outside the skull? We see this in other mammals.

There is less variation in brain size among Amerindians. Mesoamericans have brains as big as those we see in Canadian Amerindians.

Sean,

Didn't the decrease in brain size happen with the transition from hunting/gathering to agriculture?

Sean said...

Weren't Cromagons in Europe bigger brained than the later hunter gatherers? You've said skeletal changes occurred in hunter gatherers of the Magdalenian. I assumed these less robust bodies meant smaller brains, (though not relative to body size perhaps?) I think the reduction in robustness was feminization due to sexual selection, and that's what reduced the body and brain size of the hunter gatherers in the Magdalenian. The overall trend in hominid evolution is for a reduction in robustness. Females are less robust.

Anonymous said...

Wasn't significant expansion into southern China by the Han Chinese relatively recent?

William McNeil in Plagues and Peoples talks about how the Han suffered lots of plagues and diseases due to the warmer climate as they expanded southward and how as a result significant population was only possible relatively recently.

Anonymous said...

There is less variation in brain size among Amerindians. Mesoamericans have brains as big as those we see in Canadian Amerindians.

http://oregonstate.edu/instruct/anth/smith/TimeMach1984.pdf

True, there is less variation compared to the entire Old World, with its minima in Southern Indians / Southeast Asia and maxima in the arctic, but there is still a gradiant of around 100 cm3, around the same as between Whites and Blacks.

Ben10 said...

From an engineering point of view, the purpose of a design must comply with a multitude of factors. For example, the details of a car manufacturing can greatly vary from a cheap Kia to a Ferrari, with variations in the power extracted from the engine, which must be transmitted to the gears, then from the gears to the tires and finally from the tires to the road in the form of momentum. But the crucial factor is the carburant, because a given amount of carburant can only deliver the exact same amount of momentum weither it is a Kia or a Ferrari.
I would be surprised if it were any different for the human brain. I found a reference pointing to the human brain around 20 watts of power, that's 1/5 of the total energy available whithin a body running at 100 watts, or about 2400 kcal of food/day.
I guess the peak demand for brain power must greatly vary between a farmer/vegetarian lifestyle and a hunter/predator lifestyle.
It would make sense if hunters/predators had higher peak demand for energy that could be met with an increased brain size and an increase range in brain power consumption.
http://hypertextbook.com/facts/2001/JacquelineLing.shtml

Maybe Neanderthals were smart when hunting and stupid the rest of the day, while modern sapiens found a way to stay smart most of the time.

Anonymous said...

"especially in a social animal where as long as your IQ distribution meant you'd always have a chief and a witch doctor with a brain they could carry the rest of the group."

There's a military analogy to this in the context of a standard infantry platoon where the NCOs basically shout the grunts into adaptive behavior.

I was going to say it was a good example of the brighter ones in a group carrying the less-bright but that reminded me of something else. Some stupid people are stupid and some are average but very lazy i.e.they don't think unless they absolutely have to. That made me wonder about brains, energy costs and country people talking slow.

Probably nothing.

Peter Fros_ said...

Anon, Ben,

Good point. Big brains are metabolically costly. Whenever extra brain tissue becomes unnecessary, we see a decrease in brain size. This was the case when Europeans went from hunting and gathering to farming. They no longer had to store huge amounts of spatiotemporal information in memory (locations and trajectories of game animals, hunting routes, landmarks, etc.)

Sean,

That article seems to be misquoting John Hawks' study. He found that brain size has decreased over the past 10,000 years (not over the past 30,000).

"The scope of this decrease is remarkable: for example, within the past 10,000 years the average endocranial volume in European females reduced from a mean of 1502 ml to a recent value of 1241 ml [7]. This decrease of approximately 240 ml in 10,000 years is nearly 36 times the rate of increase during the previous 800,000 years."

http://johnhawks.net/taxonomy/term/850

Anon,

Chinese penetration of southern China seems to date to the second millennium BC (Shang dynasty). By the first millennium BC much of the south had been settled by the "Southern Han". So that's a time depth of 3,000 years or 120 to 150 generations.

Anon,

The lowest values for Amerindian brain size come from the Choctaw of the American southeast and some tribes from northern Columbia. In both cases, there is strong African and European admixture (often exceeding the degree of Amerindian ancestry).

Anon,

This is "smart fraction" theory, i.e., the success of a society depends not so much on overall mean intelligence as on the mean intelligence of the smartest tenth.

But it all depends on the kind of society. This theory could apply to a society based on slavery or serfdom, where the bulk of the population performs simple repetitive tasks. But even "simple" tasks aren't as simple as people think. A janitor, for instance, has to perform a wide range of repairs that are often novel and unexpected. He or she will also have to read and understand the directions for various cleansers and devices.

Anonymous said...

Chinese penetration of southern China seems to date to the second millennium BC (Shang dynasty). By the first millennium BC much of the south had been settled by the "Southern Han". So that's a time depth of 3,000 years or 120 to 150 generations.

The Southern Han was in the 10th century AD.

McNeil argues that large scale Chinese development of the South didn't occur until after the end of the Han Dynasty and that it was slow going due to disease:

http://books.google.com/books?id=f2DpAdw8l_oC&lpg=PP1&ots=3GWoX-Y9e0&dq=plagues%20and%20peoples&pg=PA101#v=onepage&q&f=false

"[M]assive development of the South did not occur until after the end of the Han Dynasty. In other words, almost a thousand years elapsed from the time when the taming of the Yellow River flood plain got seriously under way before comparable development took place in the valley of the Yangtze River.

At first glance this relatively slow pace of Chinese settlement in more southerly parts of what is today China may seem surprising. Political-military obstacles were relatively unimportant. Agricultural conditions favored settlement, since milder climates meant longer growing seasons, and more abundant rainfall removed the risk of drought that often endangered crops on unirrigated land in the North...

"Despite these obvious and real advantages, an invisible and unrecorded but, one must still believe, very potent obstacle stood in the way of the swift and successful development of rice paddies and urban life in lands to the south of the historic cradle of Chinese civilization: for in moving southward and into better farming regions, Chinese pioneers were also climbing a rather steep disease gradient!"

Sean said...

"Whenever extra brain tissue becomes unnecessary, we see a decrease in brain size. This was the case when Europeans went from hunting and gathering to farming. They no longer had to store huge amounts of spatiotemporal information in memory (locations and trajectories of game animals, hunting routes, landmarks, etc.)"

European Cromagnon females 30,000 years ago had 1550 cc so they still seem have declined 50cc by 10,000 years ago. Hawks says that brains, especially of European females, shrank in the last 10,000 years. However 30,000 years ago Cromagnon males had an average cranial capacity of 1650 cc, therefore Cromagnon males' brains shrank quite a bit between 30,000 and 10,000 years ago. I think there must have been selection for more brainpower by making the brain more efficient not 'Selection for smaller brains '. Cromagnons responded to selection for brain power by simply increasing the size of the brain until it got to a limit. After a ceiling was reached the selection for more brainpower could not increase size so it increased efficiency instead. Once brains became maximally efficient (in historical time) brain size began to increase again. Faster, Smaller, Better: Does Physics Put an Upper Limit on Brain Efficiency?



John Hawks may be interested in this. Unique Neandertal Arm Morphology Due to Scraping, Not Spearing

Sean said...

The biggest heads in Europe are found in the south west of Ireland

I think a ceiling was reached among hunter gatherers and increase in brainpower was achieved by a new and far superior organization of the neurons, possibly by making them more closely packed (easier to form connections?) Hence the reduction in size of the brain was a result of the brainpower increasing.


30,000 years ago European Cromagnon females had 1550 cc so European hunter gatherer brains shrank 50cc over the next 20,000 years in Europe. Hawks says that brains, especially of European females, shrank in the last 10,000 years. However 30000 years ago Cromagnon males had an average cranial capacity of 1650 cc, therefore (it seems to me) Cromagnon male brains shrank quite a bit between 30,000 and 10,000 years ago. I think brain shrinkage among European hunter gatherers must have been a side effect of more brainpower through improving brain organisation. I am dubious about 'Selection for smaller brains'.

Cromagnons responded to selection for brain power by simply increasing the size of the brain until it got to a limit. Once brains became maximally efficient, in historical time, 1000 years ago say, brain size began to increase again. Faster, Smaller, Better: Does Physics Put an Upper Limit on Brain Efficiency? Eventually a the limit on efficiency was reached and brains began to get bigger again with civilization.


John Hawks may be interested in this. Unique Neandertal Arm Morphology Due to Scraping, Not Spearing

Anonymous said...

Peter Frost

"This is "smart fraction" theory, i.e., the success of a society depends not so much on overall mean intelligence as on the mean intelligence of the smartest tenth."

Not in my case for the reasons you gave after. It only works in certain circumstances i.e. where there is a group engaged in a relatively simple group task and the small number of brighter ones can physically oversee the large number of dimmer ones.

In a modern society where as you say even in the case of the janitor, people have to use their own initiative for society to function then the smart fraction idea breaks down imo. The more advanced the society the higher the average needs to be.

Another military analogy would be to imagine how an army would be from countries with differing average IQs. In a very low IQ country only the senior officers can be trusted to act on their own initiative. One bump higher and initiative can go down to junior officers. Another bump and it's down to senior NCOs. A 100+ average country can rely on the initiative of individuals all the way down to squad leader with 1 or 2 spares in each squad. I'd say the latter case produces an almost infinitely more effective organization.

However in a simpler agricultural society where most people are peasants and *if* evolution selects for the minimum average IQ needed to survive then the ability of the smart fraction to partially compensate for a lower average IQ might shade the average a few points lower.

The main point though is whether evolution mildly selects against intelligence or not.

Anonymous said...

Randomly browsing and came upon a map of population density in China as part of this article

http://blogs.discovermagazine.com/gnxp/2008/02/why-brown-people-are-midgets/

It's hard to tell exactly but the density distribution seems to map quite well onto the IQ distribution.

Anonymous said...

Here's a clearer map of population density in China by province.

http://upload.wikimedia.org/wikipedia/commons/thumb/5/5a/China_Pop_Density.svg/300px-China_Pop_Density.svg.png

A pretty good fit apart from the NW province - especially the odd hole in the SE on both maps made by Jiangxi and Fujian.

Difference Maker said...

I was initially surprised at the high IQ of Gansu province in the northwest, but that is easily explained by the fact that the personnel of Jiuquan space launch center have to live somewhere.

Chinese poems of the age preceding the southern Han speak of "rivers of plague", and the short lives of officials posted there, so such matters have not quite gone unrecorded.

Anonymous said...

Gangsu was China’s “Siberia”. Mao has sent at least about a million “rightist intellectuals” (almost entirely from the right side of the bell curve) to numerous hard labour camps in Gangsu. Some of them died young, some eventually survived and returned, some survived-married-and stayed.