Saturday, 9 July 2011

Brain size and latitude: Why the correlation?


Human variation in cranial capacity. Black, 1,450 cc and over; checkerboard, 1,400-49 cc; crosshatching, 1,350-99 cc; horizontal striping, 1,300-49 cc; diagonal striping, 1,250-99 cc; dots, 1,200-49 cc; white areas, under 1,200 cc (Beals et al., 1984)

So Stephen Jay Gould was wrong, and Samuel George Morton was right. Brain size does vary among human populations. But what does this variation mean? Why does it exist?

This question is briefly addressed by Lewis et al. (2011):

[…] cranial capacity variation in human populations appears to be largely a function of climate, so, for example, the full range of average capacities is seen in Native American groups, as they historically occupied the full range of latitudes

For more information, the reader is referred to an earlier study: Beals, Smith, and Dodd (1984). The latter plotted cranial capacity from 122 human populations. The resulting map is shown above. A few caveats: there is a LOT of interpolation and extrapolation in the above map. There are no data points from Cambodia or southern Vietnam, and hence nothing to justify the very low values assigned to that region. Southern India is assigned a very low cranial capacity on the basis of a small sample that includes Veddas—a relic group of hunter-gatherers from Sri Lanka.

All in all, and keeping these caveats in mind, cranial capacity does seem to correlate with latitude. Why? According to the authors, heads are larger at higher latitudes to reduce heat loss. An object will lose less heat if its ratio of volume to surface area is high. There has thus been natural selection to make heads broader and more globular at higher latitudes. The increase in brain size is incidental.

This explanation was challenged in the comments section following the Beals, Smith, and Dodd (1984) article. A Japanese commenter, 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. Unfortunately, Morimoto provided no references to back up this counter-argument.

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.

A recent analysis has nonetheless found a significant correlation between cranial capacity and latitude among ancestral hominids in general, ranging from A. Afarensis to H. sapiens (Henneberg and Miguel, 2004). The correlation remained even when the authors controlled for each skull’s time period and, thus, was not due to the overall rise in cranial capacity over time and the parallel expansion of ancestral hominids into higher latitudes.

In sum, cranial capacity does correlate with latitude. It is less clear, however, whether this correlation is mediated by mean temperature and the need to reduce heat loss.

Higher cognitive demands at higher latitudes?

Could it be that cognitive demands increased as ancestral humans entered higher latitudes? Not because mean temperatures were lower but because the yearly cycle presented a greater diversity of environments and required much more foresight. Between ‘summer’ and ‘winter,’ the differences are much greater in the temperate and arctic zones than in the tropics.

This point is elaborated upon 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 coped with resource fluctuations and high mobility requirements by planning ahead and by developing untended devices (e.g., traps and snares) and means of food storage.

In addition, these increased cognitive demands fell on both men and women. Paternal and maternal investment were much more equal than in the tropics, where women provided for their families year-round with less male assistance (Kelly, 1995, pp. 268-269; Martin, 1974, pp. 16-18). Indeed, because men were the main food providers beyond the tropical zone, women could care for their families by developing a new range of tasks: food processing (e.g., butchery and carcass transport); shelter building; garment making; leather working; transport of material goods; etc. (Waguespack, 2005). This technological revolution would ultimately lead to what we now call ‘civilization’ (Frost, 2008).

Further thoughts

Curiously, Beals, Smith, and Dodd (1984) cite Gould’s 1978 Science article—the one claiming that Morton had unconsciously fudged his data to make brains look bigger among Europeans than among sub-Saharan Africans. Yet these authors declined to mention the inconsistencies between Gould’s findings and their own. Their reference to Gould is studiously neutral: “Critiques of the use of brain size in typology have been offered by Gould.”

There has not been much comment on the Beals, Smith, and Dodd (1984) article. The most substantive one seems to be a blog post by Robert Lindsay (2010) who calls their map a “train wreck” for claims that cranial capacity correlates with IQ:

White racists like to make a big deal about the supposed correlation between head size and intelligence and race. A nice little chart showing the basically dishonest portrayal they attempt based on cherry-picking data is below.

Methinks that Lindsay takes the fine details on that map a bit too seriously. Many of the details are simply creative extrapolation and infilling; otherwise, the map roughly corresponds with world distribution of mean IQ. Furthermore, no one is claiming that cranial capacity is the only determinant of IQ. There are undoubtedly many others: cortical surface area, myelinization of nerve fibers, relative importance of domain-general thinking, etc.

But he does make a good point about the Amerindian data.

As you can see, in the Americas, there is no good evidence whatsoever for head size and IQ. I am not aware that Amerindian IQ varies in the Americas. The average is apparently 87 across the continent. If anyone can show me that it varies by latitude, please do.

Agreed. No one can, for now. But a hypothesis is not false because no one has bothered to test it.

References

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

Frost, P. (2008). The path to civilization? Evo and Proud, March 10, 2008.
http://evoandproud.blogspot.com/2008/03/path-to-civilization.html

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.

Kelly, R.L. (1955). The Foraging Spectrum. Diversity in Hunter-Gatherer Lifeways. Washington: Smithsonian Institution Press.

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

Lindsay, R. (2010). The Head Size/IQ/Race Trainwreck, March 11
http://robertlindsay.wordpress.com/2010/03/11/the-head-sizeraceiq-trainwreck/

Martin, M.K. (1974). The Foraging Adaptation — Uniformity or Diversity? Addison‑Wesley Module in Anthropology 56.

Waguespack, N.M. (2005). The organization of male and female labor in foraging societies: Implications for early Paleoindian archaeology. American Anthropologist, 107, 666-676.

52 comments:

Beyond Anon said...

I wonder whether or not delayed maturation is in play here ... that is individuals in higher latitudes defer maturation a short while in order to invest more resources in growing certain parts of their bodies, like their brains.

Larger brains are costly in multiple areas:

1. During birth
2. During development
3. During life, because they require more energy.

From an evolutionary perspective such a thing could not happen if there is no benefit, and the suggestion that it was for energy conservation has to be the most ludicrous I have ever heard. Humans specialize in behavioral adaptations, including covering up. Energy loss can more easily be mitigated with coverings than developing larger heads or heads of a certain size. Also, those who hit upon that strategy are more likely to survive and put downward pressure on brain size.

Anonymous said...

" in the Americas, there is no good evidence whatsoever for head size and IQ."

Well, according to Lynn Arctic Peoples have a mean IQ of 91. The non-Arctic Amerindian mean is a few points lower lower.

Tod said...

Cromagnons were powerfully built and they had bigger brains than people around today. I very much doubt they were cleverer than modern people.

What about Lapps ? For their body size they have big brains (see 'Race' by John Baker)


It is difficult to believe that Inuit are not any more intelligent than equatorial Amerindians given the challenges posed by their environment. Those challenges would not select for verbal IQ though and The lives of the brain: human evolution and the organ of mind By John Scott Allen quotes a study which says that the IQ brain size correlation is much stronger for verbal IQ. Inuit do quite well some aspects of IQ.



Level I and Level II Intelligence in Inuit and White Children from Similar Environments

gcochran said...

Brain volume has apparently decreased over the past few tens of thousands of years, most rapidly during the last ten thousand years or so. It's a lot warmer than it was...

Tod said...

"most rapidly during the last ten thousand years"

Is that true everywhere or just in Europe ?

The skeletal changes could have been the result of sexual selection skewing European physiques toward the feminine. I believe Europeans are not just smaller but also less robust than the Cromagnons. Furthermore why did Europeans develop such fine facial features in the steppe tundra era. Magdelenian girl( 13000 to 15000 years ago) has the first known case of impacted wisdom teeth. Impacted teeth are a result of smaller face and jaws. It's difficult to see any advantage of that trait except where there was sexual selection of women

Tod said...

"most rapidly during the last ten thousand years"

Is that true everywhere or just in Europe ?

The skeletal changes could have been the result of sexual selection skewing European physiques toward the feminine. I believe Europeans are not just smaller but also less robust than the Cromagnons. Furthermore why did Europeans develop such fine facial features in the steppe tundra era. Magdelenian girl( 13000 to 15000 years ago) has the first known case of impacted wisdom teeth. Impacted teeth are a result of smaller face and jaws. It's difficult to see any advantage of that trait except where there was sexual selection of women

Stephen said...

The surface area heat loss hypothesis would give a larger advantage to thicker skulls than bigger brains.

Beyond Anon said...

Stephen said:


The surface area heat loss hypothesis would give a larger advantage to thicker skulls than bigger brains.


Give than man a prize.

Most likely also better head covering and perhaps thicker necks and/or more air-spaces in their skulls ...

gcochran said:


Brain volume has apparently decreased over the past few tens of thousands of years, most rapidly during the last ten thousand years or so. It's a lot warmer than it was...


Perhaps that is because of the relaxed selection meaning that humans do not need such large brains to survive.

It's very easy to die in the Antarctic. Forget one thing and you die. As it warms up there are less ways to die ...

However, it might also be that we have seen the spread of genes for more energy efficient brains (and there is evidence that those whose brains are more energy efficient are smarter) which would also relax the selection for brain size.

Anonymous said...

A Japanese commenter, 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. Unfortunately, Morimoto provided no references to back up this counter-argument.

I believe John Hawks explains this via the trend to the human wide loss of cranial capacity over the last 10,000 years, and the fact that this loss has tended to disproportiately been in the rear of the crania, which is presumably both for reasons of efficiency (more spherical volumes are biologically cheaper to produce from a volume:surface area ratio) and because the rear of the skull may house functions which tend to have relatively less utility in the Holocene environment.

Anonymous said...

What about Lapps ? For their body size they have big brains (see 'Race' by John Baker)

I believe in primates, raw brain size is more predictive of intelligence than encephalisation. Encephalisation is really only important in very small creatures AFAIK. Even cats and dogs show the relationship whereby the less encephalised creature (the dog) has higher apparent intelligence.

And it's not like there's anything in the human lineage that particularly contradicts the conception that raw brain size is more important, provided you are able to look at large Neanderthal brain sizes in respect of the facts that they may not have been able communicate near as well as we can (placing limits on their ability to use this to develop intelligence) and were likely lacking both in brain efficiency boosting mutations which both the larger populations in contemporary Africa and the post-Neanderthal agricultural world were able to produce.

UncleTomRuckusInGoodWhiteWorld said...

This constant meme that it is not difficult to live in SubSahara Africa, I find somewhat ridiculous. The continent is just too large, even south of the Sahara to make such broad general statements.

Most Africans were not hunter-gathers but small plot farmers, foragers, and hunters (there are also herders) throughout the continent.

I've actually been to two countries in the SubSahara and nowhere did I see low hanging fruit ready to pick and engorge one's self on.

There are rainy seasons that flood all vegetation, and make animals migration, but often people don't migrate with them, they wait it out. There is extreme heat, often humid, and a lot of insects, making any meat go badly much faster than in a temperate climate.

People do have ways of storing food in the ground for example. They often construct special huts, that are half built into the ground to keep grains. There are also shelters, in place like Ethiopia, where animals live in the bottom, and humans one floor above (chickens, etc), and larger animals are herded.

You definitely need planning. If you drop the typical European off in Ethiopia, Kenya, Congo, etc, in the middle of nowhere, they will be dead in a few days, due to lack of drinkable water, dangerous animals, and lack of food. The heat in some of these places alone in the dry season is enough to to dehydrate any person far faster than any temperate zone.

There might be a correlation with brain size, but as Frost mentioned, it is one of many, and it is not particularly large. What is the exact number? .3 or .4? there are obviously studies that show people who have half their brain missing who have normal IQs.

http://pmsol3.wordpress.com/2006/08/24/size-matters-but-how-much/?preview=true&preview_id=119&preview_nonce=d5040e23a0

Insightful said...

I agree with UncleTomRuckusInGoodWhiteWorld. I've been to Europe and although it is no walk in the park I think it has a pleasant climate overall, perhaps one of the most pleasant climates in the world. Europe does not have winters of Minnesota or upstate New York with sub-zero temperatures and LOTS of snow. There is abundant rainfall as well. I actually think sub-saharan Africa is harsher. Even Australia and China have more extreme climate than Europe.

droper said...

@UncleTomRuckusInGoodWhiteWorld and Insightful:

I don't think anyone is arguing that living in Europe is harsh /now/, they're talking about the long time spent in the ice ages.

Anonymous said...

Insightful said:

I agree with UncleTomRuckusInGoodWhiteWorld. I've been to Europe and although it is no walk in the park I think it has a pleasant climate overall, perhaps one of the most pleasant climates in the world. Europe does not have winters of Minnesota or upstate New York with sub-zero temperatures and LOTS of snow. There is abundant rainfall as well. I actually think sub-saharan Africa is harsher. Even Australia and China have more extreme climate than Europe.


So, what is it, in your opinion, that prevented sub-Saharan Africans and Aboriginal Australians from creating the sort of civilizations that the Chinese and the Europeans developed and from creating complex technical advances?

Was it simply white racism?

Note also that the claims are not about current conditions in northern Europe and northern Asia, but rather about the effect that the last glacial had on those groups of humans that lived in the various refugia near the shields.

Tod said...

Re G.Cochran's comment

If the Cro-Magnons' big brains (15-20% larger) were the side effect of an advanced stage of cold adaptation why were the CroMagnons so tall and long legged ? That's in contravention of Allen's rule ?

G.Cochran seems to be arguing (à la Stephen Jay Gould /Richard Lewontin) that the huge brain of Cro-Magnon man was a spandrel.
Surely bigger brains are too metabolically expensive for that.

Insightful said...

@anonymous

The first step towards civilization is the move from hunter-gatherer to agriculture, with the domestication and farming of wild crops and animals. Agricultural production leads to food surpluses, which supports sedentary societies, specialization of craft, rapid population growth, and specialization of labor. Large societies tend to develop ruling classes and supporting bureaucracies, which may lead in turn to the organization of nation states and empires.

Although agriculture arose in several parts of the world, Eurasia gained an early advantage due to the greater availability of suitable plant and animal species for domestication. In particular, Eurasia had the best collection of plants and animals suitable for domestication – barley, two varieties of wheat and three protein-rich pulses for food; flax for textiles; goats, sheep and cattle provided meat, leather, glue (by boiling the hooves and bones) and, in the case of sheep, wool. By the way, wheat and barley, which are high in fiber and nutrients, can be sown en masse with just a toss of the hand. They generated food surpluses which supported greater population growth. Such growth led to larger workforces and more inventors, artisans, etc. Grains can also be stored for longer periods of time unlike tropical crops such as bananas.

As early Middle Eastern civilizations began to trade, they found additional useful animals in adjacent territories, most notably horses and donkeys for use in transport. Eurasia as a whole domesticated 13 species of large animals (over 100 lb / 44 kg); South America just one (counting the llama and alpaca as breeds within the same species); the rest of the world none at all. Sub-Saharan Africans had mostly wild mammals, whereas Eurasians chanced to have the most docile large animals on the planet: horses and camels that are easily tamed for human transport; but their biological relatives zebras and onagers are untameable to this day; and although Asian elephants can be tamed, it is very difficult to breed them in captivity; goats and sheep for hides, clothing, and cheese; cows for milk; bullocks for tilling fields and transport; and benign animals such as pigs and chickens. Africans, developing alongside large mammals, had available lions, leopards etc.

Eurasia’s East-West orientation allowed breeds domesticated in one part of the continent to be used elsewhere through similarities in climate and the cycle of seasons. In contrast, Australia suffered from a lack of useful animals due to extinction, probably by human hunting, shortly after the end of the Pleistocene. The Americas had difficulty adapting crops domesticated at one latitude for use at other latitudes (and, in North America, adapting crops from one side of the Rocky Mountains to the other). Africa was fragmented by its extreme variations in climate from North to South: plants and animals that flourished in one area never reached other areas where they could have flourished, because they could not survive the intervening environment. Europe was the ultimate beneficiary of Eurasia's East-West orientation: in the first millennium BC, the Mediterranean areas of Europe adopted the Middle East's animals, plants, and agricultural techniques; in the first millennium AD, the rest of Europe followed suit.

The plentiful supply of food and the dense populations that it supported made division of labor possible. The rise of non-farming specialists such as craftsmen and scribes accelerated economic growth and technological progress.

jaakkeli said...

I agree with UncleTomRuckusInGoodWhiteWorld. I've been to Europe and although it is no walk in the park I think it has a pleasant climate overall, perhaps one of the most pleasant climates in the world. Europe does not have winters of Minnesota or upstate New York with sub-zero temperatures and LOTS of snow.

I disagree. I've visited America and it seemed to have a very pleasant climate; the locals told me that if I want to see any snow I have to go up to the mountains. Not at all like my home town in the taiga where I see it go down to -40 (on either scale).

You do realize that Europe is an entire continent and it's not made up of just London and Paris? Nothern Europe, Eastern Europe and the higher areas inland are plenty cold in the winter and they house a good half of the population, just not the main tourist cities. Historically, they probably had an even higher fraction of the population since coastal urban megacenters didn't exist to skew the fraction.

Nanonymous said...

huge brain of Cro-Magnon man was a spandrel. Surely bigger brains are too metabolically expensive for that.

"Surely"? Why? Not obvious at all to me. Pleiotropy works in mysterious ways. Major adaptations don't happen overnight, too.

Insightful said...

Europe is not an "entire continent" as you put it but a peninsula of peninsulas or a region of Eurasia. Eurasia is the continent. The Taiga (where your hometown is) is located outside of Europe proper on the edges and mostly in Asia. It is also sparsely populated. Hardly anyone sees the Taiga as part of Europe where the vast majority of Europeans reside. Also America (climate wise) is more diverse than Europe. America is a continent hardly moderated by the gulf stream like much of Europe and therefore it has extremes of temperatures from Texas to Maine, Minnesota to Florida.

Anonymous said...

Insightful, your just-so story is very enlightening, NOT!

You have mixed in a pinch of Jared Diamond with a soupcon of Rudyard Kipling. It's all because certain groups were fortunate to be endowed with domesticable species that they are the top dogs these days.

And yet, the Japanese, who had to adapt rice farming to their much colder climate (on average) managed to become a world economic power.

James A. Donald said...

North American Indians seem to have white or near white IQs (subjective impression, no statistical examination)

Mexicans have IQs substantially below white, similar to Afro Americans (subjective impression and anecdote, no statistical examination.)

Thus it looks to me that amerindian IQ correlates quite well with cranial capacity. (Based on statistics for cranial capacity, but merely anecdote and subjective impression for IQ)

James A. Donald said...

Cro Magnon's had larger cranial capacities. Were they smarter?

Their art is impressive - more impressive than that of modern primitives.

jaakkeli said...

Europe is not an "entire continent" as you put it but a peninsula of peninsulas or a region of Eurasia. Eurasia is the continent. The Taiga (where your hometown is) is located outside of Europe proper on the edges and mostly in Asia.

Umm, no....

First of all, the taiga was just an extreme example. It's way colder than "upstate New York" and correspondingly there's a warmer roughly "upstate New York" level of climate down south from here that covers a large part of Europe. How large? Well let's look at climate maps:

http://upload.wikimedia.org/wikipedia/commons/7/74/Koppen_World_Map.png

Basically, *over half of Europe* gets classified in the same zone as northeasternmost US and most of southern Canada. Sure, London is warm, but Eastern Europe has a contintental climate with much less influence from the sea current, Northern Europe is cold because it's so far up north and Central Europe is cold because of all the mountains.

In the US, an utterly neglible proportion of the population lives in the same kind of cold that half of Europe lives in. This is obviously because America is mostly a newly populated continent but Europe was filled up by substistence farmers. If it weren't for the language barrier, half of Moscow would probably move to Rome or whatever, but as it is it reflects historical population densities.

Again, just because you visited London or Paris and noticed that it's warm doesn't mean that most of Europe doesn't have proper, continental winters with snow and all that.

Owen Hagan said...

I have known a few geniuses (don't use the term loosely) who have had very compact skulls (one bordering on micro), but by and large most of the very smart people (also don't use that term lightly) seem to have larger skulls.

But what fascinates me most about
observing skull shapes of very smart humans is that it's brutally honest there are two types...

1. narrow skull with a high fault (see this in many northern european types)

2. wider skull (seems more common in asians and also with some very smart mediteraneous)


I've been fascinated by this observation for at least the last 20 years or so.

Anonymous said...

I live is northern New England (just two hours north of Boston). and grew up an hour west of Boston.

I do a lot of business in Western and Central Europe (nearly 8 to 10 weeks a year spent there yearly) and it is amazing how utterly harsh our climate is (Summer and Winter) vs. the average European climate (including Poland which has admittedly a stronger winter than say Flanders). The types of stucco/plaster exteriors that are common used on buildings all over Europe would not last five years in this climate.

I have put off certain exterior investments to my home because of the amount of snowfall is so great I assumed it would be ruined within a decade. It is at choices like that where I realized that future time orientation is closely linked to the climate one finds themselves in.

Of course I've long since learned to devote several days each summer to acquiring and storing firewood.

Kiwiguy said...

***1. narrow skull with a high fault (see this in many northern european types)***

There was a recent increase in size in the UK.

"According to a story on BBC News the human cranium has undergone some interesting changes over the last 600-700 years:

The two principal differences discovered were that our ancestors had more prominent features, but their cranial vault - the distance measured from the eyes to the top of the skull - was smaller.

Dr Peter Rock, lead author of the study and director of orthodontistry at Birmingham University, told the BBC News website: "The astonishing finding is the increased cranial vault heights.

"The increase is very considerable. For example, the vault height of the plague skulls were 80mm, and the modern ones were 95mm - that's in the order of 20% bigger, which is really rather a lot."

Report here

Picture illustrating the angular and linear measurements.

Kiwiguy said...

Arthur Jensen discusses causes of brain size in chapter 12 of the g factor:

"The only conceivable advantage to an increase in the size and complexity of the brain is the greater behavioral capacity this would confer.

....

What kinds of environmental pressures encountered by Homo erectus and early Homo sapiens would have selected for increased size and complexity of the brain? Evolutionists have proposed several plausible scenarios. Generally, a more complex brain would be advantageous in hunting skill, cooperative social interaction, and the development of tool use, followed by the higher-order skill of using tools to make other tools, a capacity possessed by no contemporary species other than Homo sapiens.

The environmental forces that contributed to the differentiation of major populations and their gene pools through natural selection were mainly climatic, but parasite avoidance and resistance were also instrumental. Homo sapiens evolved in Africa from earlier species of Homo that originated there. In migrating from Africa and into Europe and Asia, they encountered highly diverse climates. These migrants, like their parent population that remained in sub-Saharan Africa, were foragers, but they had to forage for sustenance under the highly different conditions of their climatically diverse habitats. Foraging was possible all during the year in the tropical and subtropical climates of equatorial regions, while in the more northern climate of Eurasia the abundance of food that could be obtained by hunting and gathering greatly fluctuated with the seasons. This necessitated the development of more sophisticated techniques for hunting large game, requiring vocal communication and cooperative efforts (e.g., by ambushing, trapping, or corralling), along with foresight in planning ahead for the preservation, storage, and rationing of food in order to survive the severe winter months when foraging is practically impossible...

Whatever bodily and behavioral adaptive differences between populations were wrought by the contrasting conditions of the hot climate of sub-Saharan Africa and the cold seasons of northern Europe and northeast Asia would have been markedly intensified by the last glaciation, which occurred approximately 30,000 to 10,000 years ago, after Homo sapiens had inhabited most of the globe. During this long period of time, large regions of the Northern Hemisphere were covered by ice and the north Eurasian winters were far more severe than they have ever been for over 10,000 years."

Kiwiguy said...

Jensen chapter 12 cont'd

"Climate has also influenced the evolution of brain size apparently indirectly through its direct effect on head size, particularly the shape of the skull. Head size and shape are more related to climate than is the body as a whole. Because the human brain metabolizes 20 percent of the body's total energy supply, it generates more heat in relation to its size than any other organ. The resting rate of energy output of the average European adult male's brain is equal to about three-fourths that of a 100-watt light bulb. Because temperature changes in the brain of only four to five degrees Celsius, are seriously adverse to the normal functioning of the brain, it must conserve heat (in a cold environment) or dissipate heat (in a hot environment). Simply in terms of solid geometry, a sphere contains a larger volume (or cubic capacity) for its total surface area than does than any other shape. Conversely, a given volume can be contained in a sphere that has a smaller surface area than can be contained by a non-spherical shape with the same surface area (an elongated oval shape, for instance). Since heat radiation takes place at the surface, more spherical shapes will radiate less heat and conserve more heat for a given volume than a non-spherical shape, and less spherical shapes will lose more heat by radiation. Applying these geometric principles to head size and shape, one would predict that natural selection would favor a smaller head with a less spherical (dolichocephalic) shape because of its better heat dissipation in hot climates, and would favor a more spherical (brachycephalic) head to accommodate a larger volume of brain matter with a smaller surface area because of its better heat conservation in cold climates. (The dolichocephalic-brachycephalic dimension is related to the head's width:length ratio, known as the cephalic index.) In brief, a smaller, dolichocephalic cranium is advantageous for thermoregulation of the brain in a hot climate, whereas a larger, brachycephalic cranium is advantageous in a cold climate. In the world's populations, head breadth is correlated about +.8 with cranial capacity; head length is correlated about +.4.

Evidence that the average endocranial volume of various populations is related to cranial shape and that both phenomena are, in some part, adaptations to climatic conditions in different regions has been shown by physical anthropologist Kenneth Beals and his co-workers..."

Anonymous said...

I'm not sure of the time scales or the archaelogy here but if the first Amerindians came in from the north did they stay at the coldest latitudes or did they head south first and only spread back up north after the more temperate latitudes filled up?

I would have kept going south until it got warm then filled America from the middle.

Anonymous said...

"It is difficult to believe that Inuit are not any more intelligent than equatorial Amerindians given the challenges posed by their environment."

The Inuit or Arab desert-dwellers or a dozen other groups living in hostile environments have the *same* challenges all year round.

I think the distinction, if there is one, is a *changing* hostile environment over a yearly cycle.

The peak line for this might run something like Finland to Japan.

Anonymous said...

"huge brain of Cro-Magnon man was a spandrel. Surely bigger brains are too metabolically expensive for that."

If larger skull size has an energy benefit in a cold climate and greater brain size has an energy disbenefit then wouldn't a compromise be a large, *thick* skull with a modest brain capacity be an option as long as bone was a good transmitter of heat?

Anonymous said...

Insightful

"I've been to Europe and although it is no walk in the park I think it has a pleasant climate overall, perhaps one of the most pleasant climates in the world."

Aryan invasions
Dorian invasions
Celtic invasions
Germannic invasions
etc

It's not that the people who lived in the middle of what is now France or Britain changed dramatically. It's that people similar to them who moved or were pushed further north into the much harsher band closer to the ice changed dramatically and then *came back* in multiple waves over two to four thousand years and mixed with the originals

(just by coincidence usually bringing with them militarily useful technological advances like better metal-working or the wheel).

bgc said...

The Eskiomos/ Inuit do have the highest IQ among Amerindians, according to this review:

http://www.gnxp.com/blog/2006/02/
world-of-difference-richard-lynn-maps.php

Peter Frost said...

All,

There are so many comments that I cannot reply to all of them. Please don't feel offended if I don't reply directly to your comment.

Greg,

Trinkaus was comparing early modern humans before and during the last ice age. There was no increase in brain size. I suspect the decrease over the last 10,000 was due to the shift from hunting and gathering to agriculture. Specifically, hunters have to store huge amounts of spatio-temporal information, i.e., current and projected locations of game animals, landmarks, layout of hunting routes, etc.

Uncle Tom,

My point wasn't that life was better in the tropical zone than in the temperate and arctic zones. Rather, it was that environmental hardship tends to follow a predictable yearly cycle outside the tropics. In the tropics, environmental hardship tends to be less predictable and more random.

There is a lot of "presentism" in the comments by you and others. Today, life is hard in sub-Saharan Africa because the population has been artificially increased well beyond the land's carrying capacity. This is a recent phenomenon.

Similarly, famine was a routine occurrence throughout all of Europe as late as the 1700s. Most farming families suffered hunger in early spring -- when the harvest from last year was running out and when this year's harvest was not yet ready.

Insightful,

Yes, I'm familiar with Jared Diamond's book. A few questions:

1. How do you explain the rise of advanced civilizations in Mesoamerica and Peru? Neither region had the benefit of east-west exchange of cultural innovations.

2. Please justify your statement that the wild precursors of Eurasian livestock were more docile than similar wild animals in Africa. I have seen this statement made repeatedly, but I have yet to see any justification. And why is it that Africa's one domesticated food animal (guinea fowl) appears to have been domesticated by women? Could it be that African men were less involved in food provisioning for their families?

UncleTomRuckusInGoodWhiteWorld said...

Peter:

To Insightful's post, I believe Diamond said that because animals in Africa evolved with higher primates (and eventually "Man") they had a natural hostility to humans, where as Eurasian primates did not tend to.

I'm not sure of Diamond's reference to this, as I no longer have his book. :-(

I will look for the info today.

UncleTomRuckusInGoodWhiteWorld said...

Here is an exact quote from Diamond, but his source is still unknown to me:

"Ironically, the long human presence in Africa is probably the reason the continent's species of big animals survive today. African animals co-evolved with humans for millions of years, as human hunting prowess gradually progressed from the rudimentary skills of our early ancestors. That gave the animals time to learn a healthy fear of man, and with it a healthy avoidance of human hunters. In contrast, North and South America and Australia were settled by humans only within the last tens of thousands of years. "

http://ngm.nationalgeographic.com/ngm/0509/resources_geo2.html

M said...

If larger skull size has an energy benefit in a cold climate and greater brain size has an energy disbenefit then wouldn't a compromise be a large, *thick* skull with a modest brain capacity be an option as long as bone was a good transmitter of heat?

Do you mean insulator?

Another alternative would be a larger brain with lower neuron density and a higher glial density and volue of fluid, but a similar number of neurons overall. That would lower some of the energetic cost of running a larger brain (and possibly some of the developmental cost) while providing the Allen's Rule advantage a larger brain has.

This is difficult to test - it's easy to get cranial capacities, but we can't really get access to brain autopsies from different groups -, though in my heart of hearts I doubt human populations which are cold adapted will have lower neuron density with their greater cranial capacity.

Notwithstanding that yes, it would seem to be cheaper to build a skull thick rather than build a larger number of glia and volume of extracellular fluid (although I'm not sure - maybe the cost of depositing bone works out heavier).

Tod said...

African animals like lions and elephants are amenable enough to be used in circuses. Europe's large animals were domesticated out of existence (ie are still around in domesticated form).

Neanderthals were hunting Europe's wild animals for how long ?

Neanderthals could not throw spears and were slow and clumsy runners. If they speared prey by running at them the final rush would immediately startle the prey into flight, Neanderthals couldn't have covered the last 10-15 meters fast enough to catch a animal stationary (if he could catch it at all, which I doubt). It would certainly be moving away from the hunter and so the spear strike would have very little actual velocity.

Neanderthals were pretty clumsy and what they probably did was lurk around woodland game trails and wait for the prey animals to walk into a prepared ambush then pop up to surround them and hence the animal would be speared as it tried to break through the cordon.

So, European animals had surely evolved to fear 'humans' by the time modern humans arrived in Europe

CroMags were were able to prey on European animals much more effectively because they had invented new projectile technology such as spear throwers.

M said...

animals in Africa evolved with higher primates (and eventually "Man") they had a natural hostility to humans, where as Eurasian primates did not tend to

Eurasian *animals*,

The idea that Chumans (or the rather rare earlier humans) would have a great selective pressure on animals in Africa above and beyond normal pressures from predation seems strange.

Plus, Eurasian animals were in the presence of an (admittedly probably lower density, or least, absolute number) of Homo Erectus (and successor) species...

It seems really hard to judge whether wolves were easier to domesticate than the African Wild Dog, or whether wild horses were originally easier to domesticate than Zebras. The only one that really seems plausible is the African Buffalo.

I'm not too sure domestication is necessarily evidence of intelligence, but I'm quite skeptical that it is explained by "African animals are hard to domesticate".

Tod said...

If you are wondering about the relationship between brain size and head size then go HERE. It shows that the low correlation of head size and brain size makes it rather far fetched to imply that brain tissue would be isometrically scaled up with head size or that brain would be metabolically cheaper than skull thickness.

The link also discusses an amazing autopsy study of brain size and intelligence. Witelson (2006)

Anonymous said...

M

"Do you mean insulator?"

Yes. It just occurred to me there might have been multiple solutions to the same problem some of which led to dead ends.

Anonymous said...

M said...

" If larger skull size has an energy benefit in a cold climate and greater brain size has an energy disbenefit then wouldn't a compromise be a large, *thick* skull with a modest brain capacity be an option as long as bone was a good transmitter of heat?"

Do you mean insulator?


The original argument was that a larger head size reduced the surface area to volume, which reduces heat outflow or something.

So the question of insulation does not apply.

If you live in an area where there are numerous Chinese and African Americans with offspring you will no doubt have noticed something amusing: The head-size differences between Chinese children and African-American children.

Peter Frost said...

Uncle Tom,

It doesn't take many generations for wild animals to learn fear of humans. In any case, archaic humans were present in Eurasia for up to a million years.

Even if one concedes these dubious points, Diamond's argument seems strange. Is he saying that early Eurasians did not hunt wild boar before domesticating them? (and is he saying that wild boar are docile?).

Africa is second only to South America in its number of mammal species. Many of them, especially the larger rodents and the medium-sized ungulates, have much potential for becoming useful livestock. Some, like the buffalo, have domesticated relatives in Eurasia.

anon666 said...

I never bought Diamond's article that the Americas lacked in animals that were possible to domesticate. Alaska and northern Canada contain caribou, which are the same species as reindeer, which the Sami -- and possibly various other Uralic-speaking peoples of northern Russia -- domesticated for transportation, meat, milk and hides. The Swedes and Russians have had some limited success with domesticating the moose, also found in North America. I remember reading an article (which I can no longer locate) saying that the Swedes devised a moose cavalry -- it didn't work because the moose were scared of gunfire, but horses had the advantage of being domesticated prior to the invention of the gun.

Domestication of animals involves their physical alteration. The horse was once too small and weak to support a mounted armored knight and were used mainly to pull chariots. They had to be bred for strength and size over the course of centuries. The moose and the caribou could have been transformed into completely different animals given enough time.

Beyond Anon said...

Peter Frost says:


It doesn't take many generations for wild animals to learn fear of humans. In any case, archaic humans were present in Eurasia for up to a million years.


I suspect that no actual learning is going on there, but rather, through their actions humans are selecting those who are genetically more wary of humans or strange behavior.

How do you determine whether it is learning that is passed on from generation to generation or selection?

This question also applies to the claims by some that the daughters of absent fathers become sexually active at an earlier age because the life-history path they select is caused by the absence of their father.

An alternative suggestion is that the mother has passed on her genes and she is the sort of woman who selects low-commitment males when looking for a sperm donor.

Ishtara said...

@Beyond Anon:
It is probably a combination of both learning and selective pressure exerted by predation.

All young mammals learn by observing and imitating the behavior of adult specimens. If the adult animals flee in panic because they've caught a human scent, the young will pick up on this behavior and learn to associate this scent with danger.

Of course at the same time, there would also have been a selection for animals that were especially wary of humans. But this takes much longer than passing on learned behavior.

labyrd@aol.com said...

Quite a large number of comments...here is one more to be likely lost in the shuffle. In general, brain size does correlate with intelligence. Of course there are exceptions, some birds appear to construct tools and exhibit a kind of, "If this, then that," cognitive ability. Whales on the other hand have not developed much in the way of observable external manipulative skills. Granted body brain ratio is an indicator but not consistently so. More likely the latitudinal size differences described in this article, have to do with relative amounts of light rather than temperature. Light processing enlargement may incidentally include overall brain growth. Another factor may be a kind of neotony - a retention of juvenal characteristics brought on by hormonal cycles lengthened by lower light periods. The result being larger head body ratio and increased brain size. The issue of intelligence is a touchy one, but I suspect that the kind of cognitive skills valued by the reigning cultures would be enhanced by larger brains.

Anonymous said...

Hi,
The answer lies in the food that was eaten. Northern climates ate more animal based omega3 fatty acids (EPA and DHA)-derived from cold water fish. In fact much of their diet was fat based, bluber from the mammals living in the colder climates. Our brains are made of fat.

-italian expat

Jean said...

See Eiluned Pearce and Robin Dunbar, Latitudinal variation in light levels drives human visual system size, Biology Letters, Published online before print July 27, 2011.

In short Dark winters = bigger eyes and therefore bigger brains for visual processing.

Anonymous said...

I'll offer the world another quasi just-so story not worst than many another, yet less heroic for nordic/caucasian/eurasian-ists to come up with: maybe if you are regularly forced to long periods of indoors limitation and inactivity, it pays off better to alocate towards being better at thinking.

Elliott Broidy said...

Lots of evidence to back this up.

Anonymous said...

The answer is meat consumption.

Increases in meat consumption start in the Lower Paleolithic, and peak in the Upper Paleolithic. Meat consumption correlates with increased cranial capacity and increased in intelligence. Cranial capacity peaks with the Neanderthal, eating 5000 calories a day of a meat-based diet. Extinction of the large herbivores and switch to grains starts the decrease in cranial capacity. Capacity varies by latitude (Inuits and meat) and matches up with avg IQ.

Case closed, no reason for any wacky theories...