Recent cognitive evolution in Europe: a new study of ancient DNA

 

Polygenic scores for alleles associated with educational attainment - Europeans of different time periods (Kuijpers et al. 2022)

 

According to a new study of ancient European DNA, cognitive evolution stagnated after the last ice age and then speeded up with the rise of farming. It stagnated again during Antiquity and then speeded up again sometime between then and now.

 

 

In my last post, I mentioned an ancient DNA study of 99 genomes from sites across Europe and Central Asia. It showed an apparent increase in mean cognitive ability between 4,560 and 1,210 years ago, as measured by alleles associated with educational attainment (Woodley et al. 2017).

 

That finding has been partially replicated by a new study of 827 genomes from ancient European remains and 250 genomes from modern Europeans. It looks like cognitive evolution stagnated after the last ice age and then speeded up with the rise of farming. It stagnated again during Antiquity and then speeded up again sometime between then and now:

 

Interestingly, while the period between the Early Upper Paleolithic and the Neolithic is characterized by stagnation or slight decrease in PRS related to intelligence, the genetic data show a clear increase in the scores for educational attainment, intelligence, and fluid intelligence from the Neolithic onwards, while the traits related with unipolar depression tend to decrease from that era on. The most significant differences can be observed comparing the pre-Neolithic and Neolithic groups, as well as the post-Neolithic and modern groups, whereas the period between the Neolithic and post-Neolithic shows a very constant distribution of PRS scores. (Kuijpers et al. 2022).

 

The authors define the time periods as follows:

 

Early Upper Paleolithic era – before 28,000 years BC

Late Upper Paleolithic era – 28,000 to 11,000 BC

Mesolithic - 11,000 to 5500 BC

Neolithic - 8,500 to 3900 BC

Post-Neolithic - 5000 BC and more recent ages (no end date given)

Modern – circa 1950 AD

 

The Mesolithic, the Neolithic, and the Post-Neolithic overlap a lot with each other. This is because their boundaries are defined by cultural changes that came to different parts of Europe at different times. The Neolithic began when hunting and gathering gave way to farming, which came later to northern Europe. Similarly, the post-Neolithic began with the advent of metallurgy, which likewise came later to northern Europe.

 

Such overlap is problematic for three reasons:

 

·         In some cases, there is uncertainty as to whether the ancient DNA came from the remains of hunter-gatherers or those of farmers.

·         “Hunter-gatherer” is not a homogeneous category. It includes not only small nomadic groups but also the hunter-fisher-gatherers of the Baltic and North Sea, who attained a degree of sedentism, population growth, and social complexity that we normally associate with farmers (Price 1991).

·         The Post-Neolithic is too long to be meaningful. It covers all of recorded history, and then some.

 

The study’s authors could have divided the Post-Neolithic into smaller time periods to give us a better look at changes during historical times. In particular, did cognitive evolution regress during Classical Antiquity? That was the preliminary finding of a team led by Michael Woodley of Menie (2019) in a study of ancient DNA from Greece. They found that mean cognitive ability increased from the Neolithic to the Mycenaean period and then decreased sometime between the latter and the present day. That study was never published, perhaps because the geographic area and the time periods were too small to provide robust results.

 

To get more robust results, we could look at ancient DNA from the entire Greco-Roman world, perhaps divided into three time periods: 5000 to 1000 BC; 1000 to 0 BC; and 0 to 500 AD. Was there a large increase in mean cognitive ability followed by an equally large decrease? Or was there simply a long period of stagnant evolution?

 

In a previous post, I argued that the culture of Classical Antiquity, particularly in its later stages, caused cognitive evolution to regress (Frost 2022). There were several reasons:

 

·         A decline in fertility and family formation, particularly among the upper classes;

·         A corresponding increase in female hypergamy, often by freed slaves, which reduced the reproductive importance of upper-class women;

·         An increase in the foreign slave population, which disrupted cognitive evolution within the local population. Even if there had been demographic overflow from the upper classes, that overflow could not have replaced the lower classes, since those classes were being replaced from external sources.

 

We need a clearer picture. According to the current data, it looks like cognitive evolution simply stagnated during the Post-Neolithic, but I suspect that time period is so broadly defined that it conceals a regression during the centuries before the fifth century collapse and the centuries immediately after.

 

References

 

Frost, P. (2022). When did Europe pull ahead? Evo and Proud, May 16. http://evoandproud.blogspot.com/2022/05/when-did-europe-pull-ahead.html

 

Kuijpers, Y., J. Domínguez-Andrés, O.B. Bakker, M.K. Gupta, M. Grasshoff, C.J. Xu, Joosten LAB, J. Bertranpetit, M.G. Netea, and Y. Li. (2022). Evolutionary Trajectories of Complex Traits in European Populations of Modern Humans. Frontiers in Genetics 13: 833190. https://doi.org/10.3389/fgene.2022.833190

 

Price, T.D. (1991). The Mesolithic of Northern Europe. Annual Review of Anthropology, 20, 211-233. Price, T. D. (1983). The European Mesolithic. American Antiquity 48(4), 761–778. https://doi.org/10.2307/279775  

 

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

 

Woodley of Menie, M.A., J. Delhez, M. Peñaherrera-Aguirre, and E.O.W. Kirkegaard. (2019). Cognitive archeogenetics of ancient and modern Greeks. London Conference on Intelligence 

https://www.youtube.com/watch?v=UES_tpDxz9A  

The Nurture of Nature

Fleet Street, watercolor by Ernest George (1839-1922). In England, middle-class families used to be so large that they overshot their niche and flooded the ranks of the lower class.

Until the last ten years it was widely believed that cultural evolution had taken over from genetic evolution in our species. When farming replaced hunting and gathering, something fundamentally changed in the relationship between us and our surroundings. We no longer had to change genetically to fit our environment. Instead, we could change our environment to make it fit us.

That view has been challenged by a research team led by anthropologist John Hawks. They found that genetic evolution actually speeded up 10,000 years ago, when hunting and gathering gave way to farming. In fact, it speeded up over a hundred-fold. Why? Humans were now adapting not only to slow-changing natural environments but also to faster-changing cultural environments, things like urban living, belief systems, and the State monopoly on violence. Far from slowing down, the pace of genetic change actually had to accelerate (Hawks et al. 2007).

These findings received a broader public hearing with the publication of The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. More recently, they have been discussed in a review article by historian John Brooke and anthropologist Clark Spencer Larsen:

Are we essentially the same physical and biological beings as Ice Age hunter-gatherers or the early farming peoples of the warming early Holocene? How has the human body changed in response to nine or ten millennia of dramatic dietary change, a few centuries of public health interventions, and a few decades of toxic environmental exposures? In short, how has history shaped biology? 

[...] But very clearly human evolution did not stop with the rise of modern humanity in the Middle to Late Paleolithic. Climatic forces, dietary shifts, disease exposures, and perhaps the wider stresses and challenges of hierarchical, literate state societies appear to have been exerting selective pressure on human genetics.

In short, we have become participants in our evolution: we create more and more of our surroundings, and these surroundings influence the way we evolve. Culture is not simply a tool we use to control and direct our environment. It is a part of our environment, the most important part, and as such it now controls and directs us.

Brooke and Larsen nonetheless feel attached to older ways of evolutionary thinking, particularly the "essentialism" of pre-Darwinian biology. We see this when they assert that “the essential modeling of the genetic code ended sometime in the Paleolithic." Actually, there was no point in time when our ancestors became essentially "human"—whatever that means. A Paleolithic human 100,000 years ago would have had less in common with you or me than with someone living 100,000 years earlier or even a million years earlier. Human evolution has been logarithmic—the changes over the past 10,000 years exceed those over the previous 100,000 years, which in turn exceed those over the previous million.

Clark’s model

Brooke and Larsen discuss Gregory Clark's work on English demography. Clark found that the English middle class expanded steadily from the twelfth century onward, its descendants not only growing in number but also replacing the lower classes through downward mobility. By the 1800s, its lineages accounted for most of the English population. Parallel to this demographic expansion, English society shifted toward "middle class" culture and behavior: thrift, pleasure deferment, increased future orientation, and unwillingness to use violence to settle personal disputes (Clark, 2007). 

Clark’s work is criticized by Brooke and Larsen on two grounds:

[... ] there is no biological evidence to support an argument for English industrial transformation via natural selection. More importantly, this was a process that—hypothetically—had been at work around the world since the launch of social stratification in the Late Neolithic and the subsequent rise of state societies.

How valid are these criticisms? Let me deal with each of them.

Is social stratification the only precondition of Clark’s model?

First, it is true that many societies around the world are socially stratified, but social stratification is only one of the preconditions of Clark’s model. There are two others:

1. Differences in natural increase between social classes, with higher natural increase being associated with higher social status.

2. Porous class boundaries. The demographic surplus of the middle and upper classes must be free to move down into and replace the lower classes.

These preconditions are not met in most socially stratified societies. Brooke and Larsen are simply wrong when they say: "The poor died with few or no children everywhere in the world, and across vast stretches of human history." In reality, there have been many societies where fewer children were born on average to upper-class families than to lower-class families. A notable example is that of the Roman Empire, particularly during its last few centuries: upper-class Romans widely practiced abortion and contraception (Hopkins 1965). A similar situation seems to have prevailed in the Ottoman Empire. By the end of the eighteenth century, Turks were declining demographically in relation to their subject peoples, perhaps because they tended to congregate in towns and were more vulnerable to the ravages of plague and other diseases (Jelavich and Jelavich, 1977, pp. 6-7)

Nor are class boundaries always porous. Social classes often become endogamous castes. This can happen when a social class specializes in "unclean" work, like butchery, preparation of corpses for burial, etc. This was the case with the Burakumin of Japan, the Paekchong of Korea, and the Cagots of France (Frost 2014). Because of their monopoly over a despised occupation, they were free from outside competition and thus had the resources to get married and have enough children to replace themselves. This was not the case with the English lower classes, who faced competition from “surplus” middle-class individuals between the twelfth and nineteenth centuries. Such downward mobility is impossible in caste societies, where “surplus” higher-caste individuals are expected to remain unmarried until they can find an appropriate social situation. 

A caste society thus tends to be evolutionarily stagnant. Lower castes in particular tend to preserve mental and behavioral predispositions that would otherwise be removed from the gene pool in a more fluid social environment.

Why did class boundaries remain porous in England? The reason was probably the greater individualism of English society, particularly its expanding middle class. Sons were helped by their parents, but beyond a certain point they were expected to shift for themselves. My mother’s lineage used to be merchants on Fleet Street in London. They were successful and had such large families that they overshot their niche. By the nineteenth century, some of them had fallen to the level of shipbuilding laborers, and it was as such that they came to Canada.

Is biological evidence lacking for Clark's model?

Brooke and Larsen are on firmer ground when they say that Clark's model is unsupported by biological evidence. There is certainly a lack of hard evidence, but the only possible hard evidence would be ancient DNA. If we could retrieve DNA from the English population between the 12th and 19th centuries, would we see a shift toward alleles that support different mental and behavioral traits? That work has yet to be done. 

Nonetheless, a research team led by Michael Woodley has examined ancient DNA from sites in Europe and parts of southwest and central Asia over a time frame extending from 4,560 and 1,210 years ago. During that time frame, alleles associated with high educational attainment gradually became more and more frequent. The authors concluded: "This process likely continued until the Late Modern Era, where it has been noted that among Western populations living between the 15th and early 19th centuries, those with higher social status […] typically produced the most surviving offspring. These in turn tended toward downward social mobility due to intense competition, replacing the reproductively unsuccessful low-status stratum […] eventually leading to the Industrial Revolution in Europe" (Woodley et al. 2017).

Again, work remains to be done, particularly on the genetic profile of the English population between the twelfth and nineteenth centuries, but the existing data do seem to validate Clark's model for European societies in general. Indeed, psychologist Heiner Rindermann presents evidence that mean cognitive ability steadily rose throughout Western Europe during late medieval and post-medieval times. Previously, most people failed to develop mentally beyond the stage of preoperational thinking. They could learn language and social norms but their ability to reason was hindered by various impediments like cognitive egocentrism, anthropomorphism, finalism, and animism (Rindermann 2018, p. 49). From the sixteenth century onward, more and more people reached the stage of operational thinking. They could better understand probability and cause and effect and could see things from the perspective of another person, whether real or hypothetical (Rindermann 2018, pp. 86-87).

As the “smart fraction” became more numerous, it may have reached a threshold where intellectuals were no longer isolated individuals but rather communities of people who could interact and exchange ideas. This was one of the hallmarks of the Enlightenment: intellectuals were sufficiently large in number to meet in clubs, “salons,” coffeehouses, and debating societies.

References

Brooke, J.L. and C.S. Larsen. (2014).The Nurture of Nature: Genetics, Epigenetics, and Environment in Human Biohistory. The American Historical Review 119(5): 1500-1513

https://doi.org/10.1093/ahr/119.5.1500 

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

Clark, G. (2009a). The indicted and the wealthy: surnames, reproductive success, genetic selection and social class in pre-industrial England.

http://www.econ.ucdavis.edu/faculty/gclark/Farewell%20to%20Alms/Clark%20-Surnames.pdf  

Clark, G. (2009b). The domestication of man: The social implications of Darwin. ArtefaCTos 2: 64-80. 

https://www.researchgate.net/publication/277275046_The_Domestication_of_Man_The_Social_Implications_of_Darwin 

Cochran, G. and H. Harpending. (2009). The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. New York: Basic Books. 

Frost, P. (2014). Burakumin, Paekchong, and Cagots. ResearchGate

https://www.researchgate.net/publication/260286339_Burakumin_Paekchong_and_Cagots

Hawks, J., E.T. Wang, G.M. Cochran, H.C. Harpending, and R.K. Moyzis. (2007). Recent acceleration of human adaptive evolution. Proceedings of the National Academy of Sciences (USA) 104: 20753-20758.

https://www.researchgate.net/profile/Henry_Harpending/publication/5761823_Recent_Acceleration_of_Human_Adaptive_Evolution/links/0c9605240c4bb57b55000000.pdf

Hopkins, K. (1965). Contraception in the Roman Empire. Comparative Studies in Society and History 8(1): 124-151.

https://doi.org/10.1017/S0010417500003935

Jelavich, C. and B. Jelavich. (1977). The Establishment of the Balkan National States, 1804-1920. Seattle: University of Washington Press.

Rindermann, H. (2018). Cognitive Capitalism. Human Capital and the Wellbeing of Nations. Cambridge University Press.

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(4): 271-280.

https://doi.org/10.1017/thg.2017.37  

A new yardstick

If we look at ancient DNA from 4,560 to 1,210 years ago, we see a steady increase over time in the number of genetic variants that are linked to high educational attainment (Woodley et al. 2017)

Four years ago I discussed genetic variants that seem to favor high educational attainment (Frost 2014). They’re found at single nucleotide polymorphisms (SNPs), and their incidence varies from one human population to another. In all but one case, they are specific to humans and not shared with ancestral primates. 

Davide Piffer has been interested in these SNP variants, seeing them as a possible way to measure how genes contribute to intelligence in different populations. By looking up population data, he can calculate their average incidence for a given group of people. This measure is called the “cognitive polygenic score.”

When he wrote up his latest paper (Piffer 2017a), only nine of these variants were known. For each geographic region, the scores were as follows:

Sub-Saharan Africans – 18%

Amerindians – 25%
North Africans – 30%
Oceanians (Papuans, Melanesians) – 34%
Southeast Asians – 35%
West Asians – 38%
Middle Easterners – 40%
Europeans – 41%
Siberians – 43%
East Asians – 45%

This regional breakdown is open to criticism. Sardinians (32%) were not included in the European category, and Mongolians (49%) were grouped with East Asians rather than with Siberians. The distinction between Middle Easterners and West Asians is not clear to me. The Amerindian category is based on a few small groups. And who is included in the Southeast Asian category? Only Cambodians?

When Piffer compared these scores with the results of IQ tests in these regions, he found a high correlation of 0.9. That is high, higher than what I would expect, given the quality of the data, especially for mean IQ, and the very disparate nature of the two datasets.

Over a two-year period Piffer submitted his paper to Intelligence, resubmitted it, had it rejected, and then resubmitted it to Frontiers in Psychology, where it was accepted by the reviewers before being rejected by the editor. It is now sitting in the limbo of a preprint repository (Piffer 2017a).

Meanwhile, the number of these SNPs has continued to grow. A research team led by Aysu Okbay identified 74 SNPs that are associated with educational attainment (Okbay et al. 2016). Another team led by David Hill reported 107 in their initial preprint and 187 in their published paper (Hill et al. 2018). 

Piffer (2017b) repeated his analysis, now using the 107 SNPs that Hill’s team had identified. The geographic pattern still held up but was weaker, the correlation being only 0.64. This lower score is actually more in line with what I would expect. It diverges the most from mean IQ in two geographic areas:

1. South Asia (Pakistan, India) - South Asians seem to do worse on IQ tests than their genetic endowment predicts. Why? Is it the culture? The diet? Inbreeding? Perhaps language. IQ tests are often administered in a language (English, Hindi, Urdu) that may be the second language of the person taking it. Or perhaps South Asian educational attainment is determined not only by IQ but also by qualities like the ability to sit still and not make a ruckus in class.

2. The Mende of Sierra Leone - For some reason, the Mende have a higher cognitive polygenic score than any other African population. This might be a real finding, or a typo.

Another research team, led by Michael Woodley, has compared the Okbay dataset with ancient DNA to see whether the cognitive polygenic score has increased over time, specifically between 4,560 and 1,210 years ago. The DNA was retrieved from European sites and a few sites from southwest and central Asia. The result? The cognitive polygenic score did increase over time. People on average had more and more of the alleles that favor educational attainment. The authors note that IQ alone may not be responsible:

[...] While the increase in these variants over time is certainly consistent with the expectation of rising GCA [general cognitive ability], the possibility that their increase indicates a simultaneous rise in other factors that make unique contributions to educational attainment (such as 'slow' life history or 'high-K' social cognitive characteristics) cannot be ruled out. (Woodley et al. 2017; references within quote removed)

The new mental/behavioral package developed through a process of feedback with the cultural environment. This gene-culture coevolution likely continued into recent times:

This process likely continued until the Late Modern Era, where it has been noted that among Western populations living between the 15th and early 19th centuries, those with higher social status (which shares genetic variance with, and is therefore a proxy for GCA) typically produced the most surviving offspring. These in turn tended toward downward social mobility due to intense competition, replacing the reproductively unsuccessful low-status stratum and effectively 'bootstrapping' those populations via the application of high levels of skill to solving problems associated with production and industry, eventually leading to the Industrial Revolution in Europe. (Woodley et al. 2017; references within quote removed)

Conclusion

More and more SNPs are being linked to educational attainment. The total is now in the triple digits. That’s still less than the thousands of genes that influence intelligence, but there is no need to identify most of them to spot general trends. Selection acts on phenotype, not on genotype. Selection for intelligence should therefore impact all of these SNPs in the same direction. It’s like estimating the proportions of different colors in a bowl of Smarties. You don’t have to count every last one. Just pick out a handful at random and count the colors.

Four years ago only 7 SNPs had been linked to educational attainment. Now we have 187. In another four years we’ll probably have more than a thousand. All the same, I doubt that the overall geographic pattern will change much. The problems lie elsewhere:

-          Genetic data may be lacking for some unmixed groups, particularly Amerindians.

-          The relationship between intelligence and cognitive polygenic score may not be linear.

-          We may be relying too much on educational attainment as a proxy for IQ (which itself is a proxy for intelligence).

When I was in public school, girls did better than boys in almost every subject. They had good attendance, always took notes, and did their homework. Boys got bored more easily and spent more time fidgeting, daydreaming, and drawing pictures in their notebooks. This sex difference exists in all cultures, but it seems greater in some than in others.

How useful is educational attainment as a proxy for IQ? Yes, these two measures correlate highly with each other (Rindermann 2018, pp. 51-54), but this high correlation is based on studies from WEIRD countries (Western, educated, industrialized, rich, and democratic). Does it hold up on a global scale? I’m not so sure.

References

Frost, P. (2014). Population differences in intellectual capacity: a new polygenic analysis, Evo and Proud, March 8

http://evoandproud.blogspot.ca/2014/03/population-differences-in-intellectual.html

Hill, W. D., R.E. Marioni, O. Maghzian, S.J. Ritchie, S.P. Hagenaars, A.M. McIntosh, C.R. Gale, G. Davies, I.J. Deary. (2018). A combined analysis of genetically correlated traits identifies 187 loci and a role for neurogenesis and myelination in intelligence. Molecular Psychiatry

https://doi.org/10.1038/s41380-017-0001-5

Okbay, A., J.P. Beauchamp, M.A. Fontana, J.J. Lee, T.H. Pers, C.A. Rietveld, et al. (2016). Genome-wide association study identifies 74 loci associated with educational attainment. Nature 533: 539-542.

http://www.nature.com/articles/nature17671

Piffer, D. (2017a) Evidence for Recent Polygenic Selection on Educational Attainment and Intelligence Inferred from GWAS Hits: A Replication of Previous Findings Using Recent Data. Preprints, June 8

https://www.preprints.org/manuscript/201706.0039/v1

Piffer, D. (2017b). Piffer's results replicated (again) by latest GWAS (N=147,194), toppseudoscience, July 21

https://topseudoscience.wordpress.com/2017/07/21/piffers-results-replicated-again-by-latest-gwas-n147194/comment-page-1/#comment-95

Rindermann, H. (2018). Cognitive Capitalism. Human Capital and the Wellbeing of Nations. Cambridge University Press.

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(4): 271-280.

https://doi.org/10.1017/thg.2017.37 

What happened in the 1980s to reaction time?

 

A steady increase in reaction time seems to begin circa 1980 in Sweden, Great Britain, and the United States (h/t to hbd* chick)

 

Has reaction time been steadily increasing from generation to generation? This was the finding of a paper last year, which argued that mean IQ had fallen in Britain by 13 points since Victorian times (Woodley et al., 2013). The problem here was not the extrapolation from reaction time to IQ, which in any case should not have changed over the past century. The problem was the possibility of sampling bias. The early samples (from the Victorian age) were slanted toward people of elite origin. In one case, they were University of Chicago students; in the other, museum visitors who had paid to take the reaction test. In contrast, the recent samples were much more representative, largely because the educational system had become more universal. Thus, the drop in reaction time over time may be largely, if not wholly, an artefact of better sampling of the general population (hbd* chick, 2013).

This criticism seems less applicable to a study of this drop in more recent times. This study was presented as a conference paper and only the abstract is available. But it does seem interesting:

Here, we show that change in genetic intelligence can be estimated, independently of the Flynn effect, by way of simple reaction time (RT). Data from three studies with different samples from Sweden, UK, and USA converge at an RT increase of 0.7-0.9 ms per year, which corresponds to a decrease in intelligence of between 4 and 5 IQ points per generation, or 1.3-1.7 points per decade in these countries. (Madison, 2014)

That’s a big jump in reaction time. Moreover, most of the increase seems to be squeezed into the last six years of the study, from 1980 to 1985 (see above chart). No selection pressure could have produced such a change over such a short time. So what could possibly be going on here?

Keep in mind that Sweden, the United Kingdom, and the United States are not closed systems. All three countries are open to the world, and the early 1980s corresponded to a time when they became much more open. Consequently, we are not looking at change within a population, but rather the replacement of one population by another, and this change would have been most noticeable in the school classrooms where these tests were conducted.

The other finding of this study is that the Flynn Effect has been masking a decline in intellectual capacity. Yes, we’re getting better at giving standardized answers to standardized questions, but this change doesn’t reflect an actual increase in intelligence. We’re just allocating more and more mental resources to the task of test-taking. The reaction time data suggest that real intellectual capacity has been declining since circa 1980.

At the same conference, Armstrong (2014) likewise argues that the Flynn Effect may be illusory for the most part:

However, "general intelligence", the biological substrata which cause the positive manifold amongst different IQ tests, has not increased, since the sizes of Flynn effects on different tests are inversely related to those tests' g loadings. The same pattern holds amongst items. Thus, for example, vocabulary size (generally the most or among the most g loaded tests) has shown a small Flynn effect, and by some measures even a decline. However, the "Coding" test (from the Wechsler) or the "Draw-a-Man" test both have low g loadings and have shown very large Flynn effects.

To date, Madison’s paper is unavailable. All we have is an abstract that raises more questions than it answers. We will have to wait for the full paper before a thorough assessment can be made.

 

References

 

Armstrong, E. (2014). LCI14 Elijah Armstrong on Rule Dependence, London Conference on Intelligence, Psychological comments, May 1

http://drjamesthompson.blogspot.co.uk/2014/05/lci14-elijah-armstrong-on-rule.html  

Hbd* chick (2013). a response to a response to two critical commentaries on woodley, te nijenhuis & murphy (2013), hbd* chick, May 27

http://hbdchick.wordpress.com/2013/05/27/a-response-to-a-response-to-two-critical-commentaries-on-woodley-te-nijenhuis-murphy-2013/  

Madison, G. (2014). Increasing simple reaction times demonstrate decreasing genetic intelligence in Scotland and Sweden, London Conference on Intelligence, Psychological comments, April 25

#LCI14 Conference proceedings
http://drjamesthompson.blogspot.co.uk/2014/04/lci14-questions-on-intelligence.html  

Woodley, M.A., J. Nijenhuis, and R. Murphy. (2013). Were the Victorians cleverer than us? The decline in general intelligence estimated from a meta-analysis of the slowing of simple reaction time, Intelligence, 41, 843-850.

http://lezgetreal.com/wp-content/uploads/2013/05/were-the-victorians-smarter-than-us.pdf   

The riddle of Microcephalin

 

World distribution of the recent Microcephalin allele. The prevalence is indicated in black and the letter 'D' refers to the 'derived' or recent allele (Evans et al., 2005)

 

Almost a decade ago, there was much interest in a finding that a gene involved in brain growth, Microcephalin, continued to evolve after modern humans had begun to spread out of Africa. The 'derived' allele of this gene (the most recent variant) arose some 37,000 years ago somewhere in Eurasia and even today is largely confined to the native populations of Eurasia and the Americas (Evans et al., 2005).

Interest then evaporated when no significant correlation was found between this derived allele and higher scores on IQ tests (Mekel-Bobrov et al, 2007; Rushton et al., 2007). Nonetheless, a later study did show that this allele correlates with increased brain volume (Montgomery and Mundy, 2010).

So what is going on? Perhaps the derived Microcephalin allele helps us on a mental task that IQ tests fail to measure. Or perhaps it boosts intelligence in some indirect way that shows up in differences between populations but not in differences between individuals.

The second explanation is the one favored in a recent study by Woodley et al. (2014). The authors found a high correlation (r = 0.79) between the incidence of this allele and a population's estimated mean IQ, using a sample of 59 populations from throughout the world. They also found a correlation with a lower incidence of infectious diseases, as measured by DALY (disability adjusted life years). They go on to argue that this allele may improve the body’s immune response to viral infections, thus enabling humans to survive in larger communities, which in turn would have selected for increased intelligence:

Bigger and more disease resistant populations would be able to produce more high intelligence individuals who could take advantage of the new cognitive opportunities afforded by the social and cultural changes that occurred over the past 10,000 years. (Woodley et al., 2014)

Bigger populations would also have increased the probability of “new intelligence-enhancing mutations and created new cognitive niches encouraging accelerated directional selection for the carriers of these mutations.” A positive feedback would have thus developed between intelligence and population density:

[…] the evolution of higher levels of intelligence during the Upper Paleolithic revolution some 50,000 to 10,000 ybp may have been necessary for the development of the sorts of subsistence paradigms (e.g. pastoralism, plant cultivation, etc.) that subsequently emerged. (Woodley et al., 2014)

 

 
What do I think?

I have mixed feelings about this study. Looking at the world distribution of this allele (see above map), I can see right away a much higher prevalence in Eurasia and the Americas than in sub-Saharan Africa. That kind of geographic distribution would inevitably correlate with IQ. And it would also correlate with the prevalence of infectious diseases.

Unfortunately, such correlations can be spurious. There are all kinds of differences between sub-Saharan Africa and the rest of the world. One could show, for instance, that per capita consumption of yams correlates inversely with IQ. But yams don't make you stupid.

More seriously, one could attribute the geographic range of this allele to a founder effect that occurred when modern humans began to spread out of Africa to other continents. In that case, it could be junk DNA with no adaptive value at all. There is of course a bit of a margin between its estimated time of origin (circa 37,000 BP) and the Out of Africa event (circa 50,000 BP), but that difference could be put down to errors in estimating either date.

No, I don't believe that a founder effect was responsible. A more likely cause would be selection to meet the cognitive demands of the First Industrial Revolution, when humans had to create a wider range of tools to cope with seasonal environments and severe time constraints on the tasks of locating, processing, and storing food. This allele might have helped humans in the task of imagining a 3D mental “template” of whatever tool they wished to make. Or it might have helped hunters store large quantities of spatio-temporal information (like a GPS) while hunting over large expanses of territory. Those are my hunches.

I don't want to pooh-pooh the explanation proposed in this study. At times, however, the authors' reasoning seems more than a bit strained. Yes, this allele does facilitate re-growth of neural tissue after influenza infections, probably via repair of damaged DNA, but the evidence for a more general role in immune response seems weak. More to the point, the allele’s time of origin (39,000 BP) doesn't correspond to a time when humans began to live in larger, more sedentary communities. This was when they were still hunter-gatherers and just beginning to spread into temperate and sub-arctic environments with lower carrying capacities. Human population density was probably going down, not up. It wasn't until almost 30,000 years later, with the advent of agriculture, that it began to increase considerably.

The authors are aware of this last point and note in it their paper. So we come back to the question: what could have been increasing the risk of disease circa 39,000 BP? The authors suggest several sources of increased risk: contact with archaic hominins (Neanderthals, Denisovans), domestication of wolves and other animals, increasing population densities of hunter-gatherers, and contact by hunter-gatherers with new environments. Again, this reasoning seems to push the envelope of plausibility. Yes, Neanderthals were still around in 39,000 BP, but they had already begun to retreat and by 30,000 BP were extinct over most of their former range. Yes, we have evidence of wolf domestication as early as 33,000 BP, but livestock animals were not domesticated until much later. Yes, there was a trend toward increasing population density among hunter-gatherers, but this was not until after the glacial maximum, i.e., from 15,000 BP onward. Yes, hunter-gatherers were entering new environments, but those environments were largely outside the tropics in regions where winter kills many pathogens. So disease risk would have been decreasing.

I don’t wish to come down too hard on this paper. There may be something to it. My fear is simply that it will steer researchers away from another possible explanation: the derived Microcephalin allele assists performance on a mental task that is not measured by standard IQ tests.

 

References 

Evans, P. D., Gilbert, S. L., Mekel-Bobrov, N., Vallender, E. J., Anderson, J. R., Vaez-Azizi, L. M., et al. (2005). Microcephalin, a gene regulating brain size, continues to evolve adaptively in humans, Science, 309, 1717-1720.

http://www.fed.cuhk.edu.hk/~lchang/material/Evolutionary/Brain%20gene%20and%20race.pdf  

Mekel-Bobrov, N., Posthuma, D., Gilbert, S. L., Lind, P., Gosso, M. F., Luciano, M., et al. (2007). The ongoing adaptive evolution of ASPM and Microcephalin is not explained by increased intelligence, Human Molecular Genetics, 16, 600-608.

http://psych.colorado.edu/~carey/pdfFiles/ASPMMicrocephalin_Lahn.pdf  

Montgomery, S. H., and N.I. Mundy. (2010). Brain evolution: Microcephaly genes weigh in, Current Biology, 20, R244-R246.

http://www.sciencedirect.com/science/article/pii/S0960982210000862  

Rushton, J. P., Vernon, P. A., and Bons, T. A. (2007). No evidence that polymorphisms of brain regulator genes Microcephalin and ASPM are associated with general mental ability, head circumference or altruism, Biology Letters, 3, 157-160.

http://semantico-scolaris.com/media/data/Luxid/Biol_Lett_2007_Apr_22_3(2)_157-160/rsbl20060586.pdf  

Woodley, M. A., H. Rindermann, E. Bell, J. Stratford, and D. Piffer. (2014). The relationship between Microcephalin, ASPM and intelligence: A reconsideration, Intelligence, 44, 51-63.

http://www.sciencedirect.com/science/article/pii/S0160289614000312