How some populations adapt to vitamin D scarcity

 

Vitamin D metabolism varies from one human population to another, as do most heritable traits. This is the subject of a review article I’ve recently published in the journal Nutrients. Here is the abstract:

 

 

Vitamin D metabolism differs among human populations because our species has adapted to different natural and cultural environments. Two environments are particularly difficult for the production of vitamin D by the skin: the Arctic, where the skin receives little solar UVB over the year; and the Tropics, where the skin is highly melanized and blocks UVB. In both cases, natural selection has favored the survival of those individuals who use vitamin D more efficiently or have some kind of workaround that ensures sufficient uptake of calcium and other essential minerals from food passing through the intestines. Vitamin D scarcity has either cultural or genetic solutions. Cultural solutions include consumption of meat in a raw or boiled state and extended breastfeeding of children. Genetic solutions include higher uptake of calcium from the intestines, higher rate of conversion of vitamin D to its most active form, stronger binding of vitamin D to carrier proteins in the bloodstream, and greater use of alternative metabolic pathways for calcium uptake. Because their bodies use vitamin D more sparingly, indigenous Arctic and Tropical peoples can be misdiagnosed with vitamin D deficiency and wrongly prescribed dietary supplements that may push their vitamin D level over the threshold of toxicity.

 

 

Reference

 

Frost P. (2022) The Problem of Vitamin D Scarcity: Cultural and Genetic Solutions by Indigenous Arctic and Tropical Peoples. Nutrients 14(19):4071. https://doi.org/10.3390/nu14194071

 

Cognitive ability of indigenous Arctic peoples

 

In cold environments, human cognitive ability was an adaptation not to resource scarcity, as is often claimed, but to an abundance of resources that could be exploited only through a high level of planning, coordination, and tool development.

Caribou on Thelon River (Wikicommons – Cameron Hayne)

 

 

A reader has asked me, via Twitter: “Do you have any articles as to why the IQ of Siberian and Inuit peoples is lower than Northern Europeans despite similarly cold climate?”

 

Actually, indigenous Arctic peoples seem to be close to the global maximum of cognitive ability. It is also true, however, that the maximum is at more temperate latitudes, specifically within two broad regions:

 

·         East Asia – this is a “plateau” of populations with consistently high mean IQ, i.e., Chinese, Koreans, and Japanese. For Unz (2013), this plateau arose during the time of recorded history through the upper classes continually replacing the lower classes: “Each generation, the poorest disappeared, the less affluent failed to replenish their numbers, and all those lower rungs on the economic ladder were filled by the downwardly mobile children of the fecund wealthy.” A secondary cause was the imperial examination for civil-service jobs: "in China the proud family traditions would boast generations of top-scoring test-takers, along with the important government positions that they had received as a result."

 

·         Europe – this second plateau likewise arose during the time of recorded history, at first slowly during antiquity and then more rapidly during the late medieval to early modern period (Clark 2007; Woodley 2017). The latter increase was driven by expansion of the middle class, particularly by craftspeople who participated in the proto-industrial revolution of the 15th to early 19th centuries. There are thus “peaks” in the plateau, notably Ashkenazi Jews and the descendants of cottage-industry communities in Ulster, Lancashire, Yorkshire, Brittany, Flanders, Alsace, Westphalia, Saxony, the Zurich uplands, the Piedmont, and Lombardy (Cochran et al. 2006; Dunkel et al. 2019; Frost 2007; Piffer 2019; Seccombe 1992, pp. 205-217). Those communities contributed disproportionately to European population growth through early marriage and high childbearing, thus changing Europe’s cognitive landscape (Seccombe 1992, pp. 205-217). 

      The fatalism of serfs gave way to the rationalism of craftspeople: "The life-choices that structure family continuity through time had more predictable consequences; critical objectives could be achieved more regularly. Increasingly, the problem of uncontrolled randomness in life's fortunes was addressed through the calculus of probabilities, rather than through ritual, prayer, pleas for divine intercession, and stoicism ..." (Seccombe 1992, p. 212). 

There is another high-IQ peak among the Finns (Piffer 2019), for reasons that remain uncertain (Late transition from hunting to farming? Absence of serfdom?).

 

If cold climates select for cognitive ability, why do we find maximum cognitive ability at temperate latitudes? This is the apparent contradiction I address in my 2019 paper. In short, I argue that cold climates selected for cognitive ability only when humans were hunter-gatherers. This selection was driven not by resource scarcity, as is often claimed, but rather by an abundance of resources that could be exploited only through a high level of planning, coordination, and tool development (Frost 2019). With the advent of farming, and increasing social complexity, the pressure of selection shifted southward to environments that imposed new cognitive challenges: literacy and numeracy, state formation, laws and law enforcement, social stratification, expansion of the built environment, growth of music, literature, and the fine arts, development of religious beliefs and practices, construction of roads and other infrastructures, and so on.

 

This cognitive evolution initially went farther in the Middle East. Then, sometime around the 16th century, that region seemed to hit a ceiling as the pace of social complexification slowed down. The slowdown had several causes. First, there was demographic stagnation and loss of food production, due to the cumulative effects of erosion, salinization, and overgrazing. Second, there were ideological constraints. Although Islam was not alone in seeking to limit the free expression of ideas, it was more effective than Christianity in preventing the rise of a secular intellectual class that could spur progress in science and technology. Third, a true market economy failed to develop in the Middle East. The concept of trade was widely understood, but production of goods and services remained mostly within the household, i.e., family members, servants and, more broadly, relatives and in-laws. As a result, the market could not replace kinship as the main organizing principle of society.

 

Finally, and perhaps most importantly, cognitive evolution continued in Europe and East Asia because their lower classes were continually replaced, demographically, by their middle and upper classes. This process, described by Gregory Clark for England and Ron Unz for China, has three key elements:

 

1. Social class correlates positively with IQ.

 

2. Social class correlates positively with reproductive success. Lower classes fail to reproduce themselves, whereas higher classes more than reproduce themselves.

 

3. There are no barriers to downward social mobility. Lower classes are thus continually replaced by the demographic overflow of higher classes (Clark 2007; Unz 2013).

 

These three elements are not universal. Hunter-gatherers and simple farming societies have little or no social stratification. Other societies are stratified but have no State that can monopolize the use of violence. There is instead an ongoing free-for-all that selects for ruthlessness, charisma, and the ability to mobilize male violence. Finally, some societies are so stratified that downward mobility is impossible. Social classes are permanent “castes.”

 

In sum, cognitive evolution was initially driven by cold climate at higher latitudes and later by increasing social complexity at lower latitudes. Some higher-latitude groups then moved south to exploit the opportunities being created by increased social complexity. Those groups were not the ones who initiated the transition to farming, sedentism, and social complexity. Instead, they arrived after the fact, being cognitively pre-adapted for the opportunities that others had created and thus better able to pursue this evolutionary trajectory (Frost 2019).

 

Studies of cognitive ability in Arctic peoples

 

To return to the original question, indigenous Arctic peoples seem to be close to the global maximum of cognitive ability, but the evidence is limited and questionable. This situation has three causes:

 

·         Difficulties in administering IQ tests to people who are unfamiliar not only with modern concepts but also with the modern question-and-answer paradigm. Traditionally, indigenous Arctic people learn not by asking questions but by observing a “master” and then copying whatever he or she does. Asking questions can also be impolite, especially if too many are asked in rapid succession. I should point out that the same difficulties used to exist in Western societies. People in Britain and North America were unfamiliar with standardized written tests until the rise of publicly funded schools and competitive civil-service exams in the late 19th century (Wikipedia 2022). It wasn’t because people got smarter that mean IQ rose during the 20th century. They just got better at taking tests.

 

·         Ideological constraints. IQ research was discouraged in the Soviet Union, partly because of the dominant belief in environmental determinism and partly because of a desire to avoid stigmatizing certain national groups. A ban on intelligence testing was thus imposed in 1936 and gradually lifted only in the 1960s and early 1970s (Grigoriev and Lynn 2009).

 

·         Lack of research on alleles associated with educational attainment. This avenue of research offers a better measure of innate cognitive ability but is still in its infancy with respect to Arctic peoples. I know of only one relevant study. Piffer (2013) found that the Met allele at COMT, a gene linked to executive function, working memory, and intelligence, is more frequent in farming societies than in hunter-gatherers, with one interesting exception: "hunter-gatherers living at high latitudes (Inuit) show high frequencies of the Met allele, possibly due to the higher pressure on technological skills and planning abilities posed by the adverse climatic conditions near the North Pole."

 

 

Siberia (Evenk, Altai, Yakuts)

 

In Siberia, IQ tests were conducted in 1929 and later in 2015-17. The first period saw testing among the Evenk of the northeast and the Altai of the south.

 

When a Binet test was administered to 5 Evenk children 7 to 19 years old, the mean score was 70.16. The study’s author reported that the children had trouble understanding units of measurement and number.

 

He reported that when Evenk children were questioned about devices for measurement, they did not have the concept of an absolute unit of measurement. They thought that the unit changed with the material measured. Bulanow [the author] reported further that when he asked Evenk adults how many children they had “It was difficult, almost impossible, to get from parents precise information as to how many of their children were alive, how many of their children had died, what was the age of their children, and so on.” (Grigoriev and Lynn 2009, p. 449)

 

When a Binet test was administered to 52 Altai children 8 to 20 years old, the mean score was 66.9. Again, the subjects had problems with units of measurement: “when they were questioned about the length of a meter, the Altai would often ask: “Which meter?” They thought that the meter in one shop could be longer than in another” (Grigoriev and Lynn 2009, p. 450). Nonetheless, adult Altai showed remarkable aptitudes in other areas of life:

 

Although adult Altai performed calculations poorly at the time of study, they showed a remarkable ability for visual estimation of large quantities. A herdsman, who could count only to 20–30, noticed very well the absence of one horse, cow or sheep in a herd of many hundreds. He looked at a huge herd and noted that a particular cow was absent. Another example of the great visualization ability of the Altai was that they could remember and showed the way through wild territory, where they had been only once many years previously (Grigoriev and Lynn 2009, p. 450)

 

In recent years, there has been a renewed effort to study cognitive ability among indigenous Siberian peoples:

 

·         Shibaev and Lynn (2015) tested 29 Evenk children and found a mean score of 80. Also tested were 13 ethnic Russian children, who had grown up under similar conditions. Their mean score was 85.

·         Shibaev and Lynn (2017) tested 287 Yakut children and 52 ethnic Russian children from eastern Siberia. The mean score was 97.0 for the Yakuts and 97.9 for the ethnic Russians.

·         Shibaev et al. (2020) tested 518 Yakut children and 956 ethnic Russian children. The age range was wider than in previous studies, and the IQ difference between the two groups seemed, in general, to be greater at younger ages than at older ones. At 9 years of age the Russians had a 3 point advantage over the Yakuts, whereas at 17 this advantage was zero. Yakut children may have a slower rate of cognitive maturation. There is also some doubt as to the comparability of the two groups, since the Russians came largely from a city (Tomsk), while the Yakuts came from a city (Yakutsk) and a small town (Vilyuysk).

 

The authors note that the differences between ethnic Russians and indigenous Siberians can be largely explained by an urban-rural divide:

 

[…] for both Russians and Yakuts the IQs of the city samples were higher than the IQs of the village samples. For the Russians, there was a difference of 10.5 IQ points between the combined city samples and the village sample, while for the Yakuts the difference was 4.4 points. The higher IQs of the city samples is a common result found in many previous studies reporting that urban populations typically obtain higher IQs than rural populations. (Shibaev and Lynn 2017)

 

Shibaev and Lynn (2017) attribute this urban-rural divide to differential migration: smarter people move to the city, and dumber people stay home in the village. I would argue that villagers are less familiar with modern concepts and the modern question-and-answer paradigm.

 

Arctic North America (Inuit)

 

Like indigenous Siberians, the Inuit (Eskimos) display an unusual ability to find their way across vast expanses of territory, a task that requires remembering huge amounts of visuospatial data. Adults are reported to have an "extraordinary ability to find their way through what appears to be a featureless terrain by remembering visual configurations [...]. According to some reports, such memories persist for long periods of time. Elderly hunters have succeeded in guiding parties through terrain seen only in their youth" (Kleinfeld 1973, p. 344)

 

Nonetheless, Inuit have done poorly in most IQ studies, especially in older studies of traditional Inuit. Kleinfeld (1973) cites several reasons:

 

Unfamiliarity with test-taking:

Eskimos' performance on standardized tests may be lowered because of their unfamiliarity with test-taking conventions and because of cultural biases of the tests. Eskimos, for example, may find it difficult to view a trivial, pointless task such as copying a design or running through a finger maze as worthy of serious concentration and maximum effort.

 

Racial context of test-taking

Eskimos, especially young males, have become increasingly antagonistic to any sort of testing and research, which they view as another form of White exploitation. Co-operation, if given at all, may be perfunctory, resulting in extremely low test scores.

 

Extreme caution during test-taking

Eskimos, especially males, have been socialized into extreme caution before making a judgment. The hunter is taught never to take risks, never to call out a hasty evaluation because the penalty can be swift death not only for himself but also for others who rely on his decision. […] Especially more traditional Eskimos tend to have a slow, cautious response style which may depress their scores on speeded figural tests.

 

Slower rate of cognitive maturation

[There is] some evidence that Eskimos' peak performance on figural tests occurs later than that of Western groups. [This] raises the possibility of a slower rate of cognitive maturation among Eskimos which would be consistent with their somewhat slower rate of physical maturation […]. If this is the case, the usual age-matched comparisons between Western and Eskimo children on figural tests may be misleading.

 

In their reviews of the literature, Kleinfeld (1973) and Taylor and Skanes (1976) note that Inuit generally outperform Whites on visual discrimination and spatial tests. Interestingly, Inuit children do almost as well as non-Inuit children on English spelling tests while doing poorly in other aspects of English, perhaps because they memorize the shapes of words. On the other hand, they underperform White children on verbal-educational and inductive reasoning tests. The latter finding may reflect lack of familiarity with English in earlier studies. When Taylor and Skanes (1976a) tested Inuit and White first graders for vocabulary and arithmetic, using the Wechsler Pre-School and Primary Scale of Intelligence, they found no significant differences between the two groups in spatial, verbal-educational, and inductive reasoning abilities. When the same researchers tested a larger sample of Inuit and White children from different age groups, using a series of digit span tests and Raven’s progressive matrices, they found that the Inuit children caught up with the White children with increasing age on the digit span tests and that the Inuit children outperformed the White children on the Raven’s progressive matrices (Taylor and Skanes 1976b).

 

Wright et al. (1996) tested the IQ of Inuit children in Arctic Quebec during the first two grades of school, using Coloured Progressive Matrices (CPM). Mean scores were consistently higher than age-appropriate U.S. norms and were comparable with data for White children in southern Quebec. In addition, the scores of children with two Inuit parents did not differ significantly from those of children with mixed Inuit/White heritage. 

 

Nonetheless, Inuit children do worse at school than other children, having not only lower rates of academic achievement but also higher dropout and suicide rates. For Clifton and Roberts (1988), the reason is inferior self-perception of their ability and less active involvement in the educational process. This mindset may be rooted in the traditional Inuit attitude toward education, where the “student” simply observes and copies the “master.”

 

In sum, the Inuit seem to have about the same level of cognitive ability as people of European origin, with perhaps some interesting differences: superior visuospatial skills, higher risk aversion, slower cognitive maturation, and a more imitative and less inquisitive approach to learning. It is still unclear whether they have lower verbal-educational and inductive reasoning abilities. In their review, McShane and Berry (1988, p. 392) conclude that indigenous Arctic peoples do well relative to Euroamerican norms, showing “high performance on both piagetian and psychometric tests of visually based spatial, analytic, disembedding, and inductive abilities.” The two researchers attribute reports of lower verbal ability to second-language familiarity with the test language. Clearly, more research is needed, if only to adapt the northern educational system to Inuit needs.

 

It must be said that the Inuit are ill-suited to the Western model of education and, more broadly, to the Western model of sedentism, individualism, and asociality. Young Inuit feel useless in that kind of society, and all too many end up committing suicide.

 

Conclusion and discussion

 

We have only a few studies of cognitive ability among indigenous Arctic peoples. This paucity is due only in part to methodological problems. In the Soviet Union, all IQ research ceased between 1936 and the 1960s. It has recommenced among indigenous Arctic peoples only over the past decade. Meanwhile, similar research in Canada and the U.S. has been nonexistent since the 1990s.

 

If we look at the existing research, we may doubt whether the subjects were fully familiar with test-taking and the modern question-and-answer paradigm. Another problem is that indigenous Arctic children seem to have a slower rate of cognitive maturation. If Yakut subjects are still catching up to Russian subjects at the age of 17, it might be more appropriate to compare the two groups at an older age. In practice, this would be difficult because young adults start following different life paths after 17. Finally, indigenous Arctic peoples may allocate their mental capacities differently, being better, for instance, at processing visuospatial data than other kinds of information. Since IQ tests have been designed for Western children, the test design may not correspond to the mental tasks that some non-Western groups prioritize.

 

Yes, dear reader, I hear you. If people do well on one cognitive task, they should do well on all others, shouldn’t they? Isn’t that what the g factor is all about? In other words, people will tap into the same mental capacity for any cognitive task.

 

The relative strength of the g factor, however, has been calculated from subjects in Western or Westernized societies. Does it have the same strength across different mental domains among people who until recently were nomadic hunters? Anthropologists, like John Berry, have argued that hunters allocate much more of their mental capacity to visuospatial orientation:

 

Hunters, by this way of thinking, require good visual acuity, keen disembedding skills and a well-developed sense of spatial orientation. To hunt successfully, the hunter must be able to discern the object of the quest (which is often embedded in a complex visual landscape), then disembed the object, and finally return to home base. In contrast, agriculturalists need not develop these particular skills, but rather they need to invest in other areas of development, such as conservation (in both the economic and the Piagetian senses) and close social interactions. (Berry 2008, p. 3)

 

It would be interesting to find out whether these skills have become hardwired to some degree through gene-culture coevolution. Are hunting peoples inherently better at orienting themselves in space? Did vast expanses of land favor the success of people who could more easily find their way across vast expanses of land? To answer that question, John Berry launched a project in the late 1980s with the geneticist L.L. Cavalli-Sforza. They wished to recruit participants among the Inuit of northern Canada and use aptitude for soapstone carving as a means to measure visuospatial skills:

 

With most individuals having had a reasonably fair chance and stimulation to become artists, one is in a better condition to study possible genetic factors contributing to artistic talent, if any. Another great advantage of carrying out this study among the Inuit is the frequency with which adoptions (also early ones, at birth) occur in this population. Frequencies of adoptions reported during the meeting varied from 15% to 30%. Adoptions allow one to distinguish cultural from biological inheritance by studying correlations of adopted children with foster relatives on one hand and biological relatives on the other. (Berry and Cavalli-Sforza 1986)

 

Cavalli-Sforza was thinking, here, along the lines of gene-culture coevolution. He had in fact been one of the founders of that paradigm, although he preferred the term “dual inheritance theory.” Now, he would have a chance to investigate it in the field.

 

Then, suddenly, he backed out of the project. For “health reasons.” Yet neither his biography nor his autobiography mentions any health problems during that period of his life.

 

 

References

 

Berry, J.W. (2008). Models of Ecocultural Adaptation and Cultural Transmission: The Example of Inuit Art, paper presented at the conference Adaptation et socialisation des minoritiés culturelles en région, June 3-4, Quebec City.

 

Berry, J.W., and L.L. Cavalli-Sforza. (1986). Cultural and Genetic Influences on Inuit Art. Report to the Social Sciences and Humanities Research Council of Canada, Ottawa.

 

Clark, G. (2007). A Farewell to Alms. A Brief Economic History of the World. Princeton University Press, Princeton and Oxford

 

Clifton, R.A. and L.W. Roberts. (1988). Social psychological dispositions and academic achievement of Inuit and non-Inuit students. Alberta Journal of Educational Research 34(4): 332–343.

 

Cochran, G., J. Hardy, and H. Harpending. (2006). Natural history of Ashkenazi intelligence. Journal of Biosocial Science 38(5): 659–693. https://doi.org/10.1017/S0021932005027069

 

Dunkel, C.S., M.A. Woodley of Menie, J. Pallesen, and E.O.W. Kirkegaard.  (2019). Polygenic scores mediate the Jewish phenotypic advantage in educational attainment and cognitive ability compared with Catholics and Lutherans. Evolutionary Behavioral Sciences 13(4): 366-375.  https://psycnet.apa.org/doi/10.1037/ebs0000158

 

Frost, P. (2007). Natural selection in proto-industrial Europe. Evo and Proud, November 16

http://evoandproud.blogspot.com/2007/11/natural-selection-in-proto-industrial.html  

 

Frost, P. (2019). The Original Industrial Revolution. Did Cold Winters Select for Cognitive Ability? Psych 1(1): 166-18. https://doi.org/10.3390/psych1010012  

 

Grigoriev, A, and R. Lynn. (2009). Studies of socioeconomic and ethnic differences in intelligence in the former Soviet Union in the early twentieth century. Intelligence 37: 447-452, https://doi.org/10.1016/j.intell.2009.05.005  

 

Kleinfeld, J.S. (1973). Intellectual Strengths in Culturally Different Groups: An Eskimo Illustration. Review of Educational Research 43(3): 341-359.

https://doi.org/10.3102%2F00346543043003341  

 

McShane, D., and J.W. Berry. (1988). “Native North Americans: Indian and Inuit Abilities.” In: S.H. Irvine and J.W. Berry (eds.) Human Abilities in Cultural Context (pp. 385-426), Cambridge: Cambridge University Press.

 

Piffer, D. (2013). Correlation of the COMT Val158Met polymorphism with latitude and a hunter-gather lifestyle suggests culture-gene coevolution and selective pressure on cognition genes due to climate. Anthropological Science 121(3): 161-171. https://doi.org/10.1537/ase.130731  

 

Piffer, D. (2019). Evidence for Recent Polygenic Selection on Educational Attainment and Intelligence Inferred from Gwas Hits: A Replication of Previous Findings Using Recent Data. Psych 1(1): 55-75. https://doi.org/10.3390/psych1010005    

 

Seccombe, W. (1992). A Millennium of Family Change. Feudalism to Capitalism in Northwestern Europe. London: Verso.

 

Shibaev, V., A. Grigoriev, E. Valueva, and A. Karlin. (2020). Differential Item Functioning on Raven’s SPM+ Amongst Two Convenience Samples of Yakuts and Russians. Psych 2(1):44-51. https://doi.org/10.3390/psych2010005

 

Shibaev, V. and R. Lynn. (2015). The Intelligence of the Evenk/Tungus of the Russian Far East. Mankind Quarterly 56(2): 202-207. http://doi.org/10.46469/mq.2015.56.2.7  

 

Shibaev, V. and R. Lynn. (2017). The Intelligence of Yakuts and Ethnic Russians in Yakutia. Mankind Quarterly 57(4): 680-686. http://doi.org/10.46469/mq.2017.57.4.11  

 

Taylor, L.J., and G.R. Skanes. (1976a). Cognitive abilities in Inuit and White children from similar environments. Canadian Journal of Behavioural Science 8(1): 1-8.

https://psycnet.apa.org/doi/10.1037/h0081930  

 

Taylor, L.J., and G.R. Skanes. (1976b). Level I and level II intelligence in Inuit and White children from Similar Environments. Journal of Cross-Cultural Psychology 7(2): 157-168.

https://doi.org/10.1177%2F002202217672004

 

Unz, R. (2013). How Social Darwinism made modern China, The American Conservative, March/April, 16-27. https://www.theamericanconservative.com/articles/how-social-darwinism-made-modern-china-248/  

 

Wikipedia (2022). Test (assessment). https://en.wikipedia.org/wiki/Test_(assessment)#West  

 

Woodley, M.A., S. Younuskunju, B. Balan, and D. Piffer. (2017). Holocene selection for variants associated with general cognitive ability: comparing ancient and modern genomes. Twin Research and Human Genetics 20: 271-280. https://doi.org/10.1017/thg.2017.37   

 

Wright, S.C., D.M. Taylor, and K.M. Ruggiero. (1996). Examining the Potential for Academic Achievement among Inuit Children: Comparisons on the Raven Coloured Progressive Matrices. Journal of Cross-Cultural Psychology 27(6): 733-753.

https://doi.org/10.1177%2F0022022196276006  

Were they right after all?

Modern humans entered the Americas from northern Eurasia. As they entered tropical environments farther south, they had to evolve new genetic adaptations from scratch. They no longer had the ones their remote forbearers had back in Africa. (Source)

OK, so modern humans have archaic admixture, and the degree of admixture seems to be highest among sub-Saharan Africans and Melanesians. But what does this factoid mean? Does it mean anything at all?

One school of thought says it means nothing at all. Ernst Mayr held this view:

The claim has been made that species owe much of their genetic variability to introgressive hybridization. However, all the evidence contradicts this conclusion so far as animals is concerned. Not only are F1 hybrids between good species very rare, but where they occur the hybrids (even when not sterile) are demonstrably of inferior viability. The few genes that occasionally introgress into the parental species are not co-adapted […] and are selected against. Introgressive hybridization seems to be a negligible source of genetic variation in animals. (Mayr, 1970, p. 80)

“Co-adaptation” means that genes are selected for their ability to work with other genes. “On one genetic background a given gene may add to the fitness of the genotype; on another genetic background the same gene may create an unbalance and produce a severely deleterious effect” (Mayr, 1970, p. 169).

Yet some genes seem to be of the “stand alone” sort. We see this when genetically modified organisms are created, such as by transferring an antibiotic-producing gene from a microbe to a cultivated plant.

Mayr also overlooked the possibility that introgressing genes might benefit a species that is expanding into new territory and gradually displacing the native species. Such genes can circumvent the need to evolve genetic adaptations that already exist in the native population. This argument was used by Greg Cochran, John Hawkes, and Henry Harpending a few years back, when they thought that the most recent microcephalin variant had introgressed from the Neanderthals. Another case of Neanderthal introgression seemed to be the diversification of European hair colors, via the MC1R gene:

A few years ago, I was thinking about Out-of-Africa, and it occurred to me that we probably picked up a lot of favorable alleles from Neanderthals […] Looking at the new article in PNAS, I'd say that Bruce Lahn and company have probably found one.[…]

Now if the Neanderthals were really effectively isolated before we expanded into their territory, they'd have a lot of significantly different alleles. Some would have involved various kinds of regional adaptations, which might be a good thing to have in Eurasia. (MC1R?) But it's entirely possible that some alleles solved adaptive problems that had existed in Africa as well - but solved them better.

Brains had expanded over the last half-million years in both Africans and Neanderthals, but it seems likely that those changes in size and structure were driven by different mutations, just as light skin in Europe and East Asia was. The Neanderthals had slightly bigger brains than Africans: obviously those brains were useful for _something_.

[…] So when you think about the cultural explosion that occurred shortly after we overwhelmed the Neanderthals (cave paintings, sculptures, new tools and weapons, all that jazz) - well, you have to wonder if assimilating a passel of adaptive alleles in a few thousand years, way more than the typical number that would arise and become established over such a short time span, didn't give us a hell of a boost. There are signs of behavioral modernity a bit earlier in Africa - but those ostrich eggshells are dull as hell compared to Gravettian cave paintings. Expansion out of Africa must itself be a sign of new capabilities (I'd bet on sophisticated language) but you only see full-fledged behavioral modernity in the European Upper Paleolithic... (Cochran, 2006)

Since then, the Neanderthal genome has been fully reconstructed. The most recent microcephalin variant isn’t on it. Nor are the European MC1R alleles. It seems that the best laid theories of mice and men gang aft agley.

No one likes to be proved wrong. Especially in public. For some time yet, certain people will be busy flogging the dead horse of Neanderthal introgression. Will they find anything? Undoubtedly. Anything to do with intelligence or artistic creativity? Probably not.

In all fairness, we’re not giving the theory of adaptive introgression a decent chance by looking only at Neanderthal admixture in modern Europeans. That degree of admixture is only 1 to 4% (perhaps less if we adjust for archaic admixture in modern Africans). We might have more luck looking at sub-Saharan Africans, who have as much as 15% archaic admixture.

In sub-Saharan Africa, the main genetic change since the advent of modern humans has been the replacement of hunter-gatherers by farming peoples. This process began perhaps 6,000 to 7,000 years ago near the Niger’s headwaters. A small core population of hoe farmers progressively expanded westward and southward, eventually occupying almost the whole of sub-Saharan Africa, except for a few marginal environments in central and southern Africa inhabited by Pygmy and Khoisan hunter-gatherers (Murdock, 1959, pp. 44, 64-68).

This new means of subsistence set off a cascade of social and, ultimately, biological changes. Year-round farming enabled women to provide for themselves and their children with little male assistance. Because more men could afford a second wife, the polygyny rate soared from around 5% of all sexual unions to 20-40%. Men now had to compete more fiercely against each other for access to women, the result being selection for greater stature, muscle mass, and bone strength. Many of these changes were and still are testosterone-mediated, i.e., through higher testosterone levels in young adult males or through testosterone receptors that bind the target molecule more effectively. Other changes may have been initially testosterone-mediated and then gradually hardwired (Frost, 2001; Frost, 2008).

A similar process has affected Amerindian farming peoples in the tropical New World, but not to the same degree. Among the Yanomamö, an agricultural people of Amazonia, 10 to 20% of all men have more than one wife at any time (Hames, 1995). They are thus more polygynous than non-tropical Amerindians but not as polygynous as tropical Africans. Their bodies likewise don’t show the same degree of robustness. Despite living in the tropics for millennia, they still look remarkably Arctic-adapted. As Holliday (1997, pp. 425-426) notes:

Despite having as much as 18,000 years of selection in environments as diverse as those found in the Old World, body mass and proportion clines in the Americas are less steep than those in the Old World. […] In fact, as Hulse (1960) pointed out, Amerindians, even in the tropics, tend to possess some “arctic” adaptations.

In Mesoamerica, farming began about 6,000 to 7,000 years ago—the same time depth as in West Africa (although there is evidence of proto-agriculture going back to 12,000 years ago in West Africa). The difference between the two culture areas seems to have been more in the speed of co-evolution with this new means of subsistence, and especially with its social consequences. Briefly put, natural selection has had less raw material to work with among tropical Amerindians than among sub-Saharan Africans. Because modern humans entered the Americas from northern Eurasia, their genetic variability had been whittled down to the bare minimum for Arctic survival. They have thus evolved more slowly away from anatomical traits and behavioral predispositions that were originally meant for Arctic environments.

This is in contrast to the relatively rapid change in morphology that we see in sub-Saharan Africa—from a small, gracile, and almost childlike appearance, as typified by Pygmies and Khoisans, to a much larger and more robust body form. Just as radical has been the shift from a low rate of polygyny to a very high one.

Did evolution get a helping hand in sub-Saharan Africa? Was this change in physique facilitated by introgression of archaic genes? Perhaps Greg Cochran and John Hawkes were right after all. They just had the wrong example.

A final point

This leads to another point. It’s inexact to say that genetic introgression speeds up evolution. Rather, it speeds up evolution along a certain trajectory … to the detriment of other possible trajectories.

Take the example of tropical Amerindians. With the advent of year-round farming, they started down the same path that sub-Saharan Africans were taking on the other side of the Atlantic, i.e., more reproductive autonomy for women, lower cost of polygyny for men, higher incidence of polygyny, more male-male competition for access to women, etc.

But their progress down that path was slower. They had less of the relevant genetic variability for natural selection to act on. Meanwhile, another path opened up. This was the one leading to the formation of more complex societies, such as the Mayans, the Toltecs, and the Aztecs in Mesoamerica, and the Incas in South America. They were able to take that path because of their relatively low level of male-male rivalry. There was consequently less need for pacification—a key precondition for development of complex social relations (i.e., State formation, specialization of labor, creation of roads and other public infrastructures, etc.).

This was not the case in sub-Saharan Africa. The high rate of polygyny, and hence male-male competition, became a serious impediment to the creation—and survival—of complex societies.

References

Cochran, G. (2006). Neanderthal introgression & microcephalin, Gene Expression, November 8

http://www.gnxp.com/blog/2006/11/neanderthal-introgression.php

Frost, P. (2008). Sexual selection and human geographic variation, Special Issue: Proceedings of the 2nd Annual Meeting of the NorthEastern Evolutionary Psychology Society. Journal of Social, Evolutionary, and Cultural Psychology, 2(4),169-191. http://137.140.1.71/jsec/articles/volume2/issue4/NEEPSfrost.pdf

Frost, P. (2001). Polygyny and sex ratios, Encyclopedia of Birth Control, V.L. Bullough (ed.), Santa Barbara (Cal.): ABC-CLIO, pp. 218-223.

Hames, R. (1995). Yanomamö, Varying Adaptations of Foraging Horticulturalists, Just in Time Anthropology series, Prentice Hall and Simon & Schuster, supplemental readings for Ember and Ember's Anthropology, 8th edition.

Holliday, T.W. (1997). Body proportions in Late Pleistocene Europe and modern human origins, Journal of Human Evolution, 32, 423-447.

Murdock, G.P. (1959). Africa. Its Peoples and Their Culture History. New York: McGraw-Hill.

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.