A new start

 

When geneticist Davide Piffer examined IQ-enhancing alleles at seven different genes, he found that their average prevalence differed among human populations, being highest in East Asians and lowest in Mbuti Pygmies (photo used with author's approval)

 

My weekly posts are now appearing on The Unz Review (http://www.unz.com/). By accepting Ron's invitation, I hope to reach a bigger audience and bring myself closer to other writers in the area of human biodiversity. When people work together, or simply alongside each other, minor differences can be ironed out and major differences narrowed or at least accepted good-naturedly. One thing I've learned is that academic debate can leave a legacy of hurt feelings. The impersonal can become personal, partly because people feel attached to their views and partly because views themselves can have personal impacts.

Working together also creates synergy. It becomes easier to identify research priorities, contact interested researchers, and end up with publishable findings. At present, most HBD research involves trawling through the literature and offering new interpretations. That's fine, but we need lab work as well. This point came up in a 2006 interview with geneticist Bruce Lahn:
 

A lot of researchers studying human population genetics and evolution are strictly data miners (i.e., they generate/publish no original data). There are limitations to such an approach, as it depends on the available data and prevents certain analyses from being performed. Do you expect to see more research groups turning into pure data mining labs in the future? Or will there still be a place for independent labs generating their own data (for example, resequencing a gene in multiple individuals to study the polymorphism)?

Given the explosion of genomic data in the last decade or so, which shows no sign of slowing down any time soon, there is likely to be a proliferation of pure data miners just because there is a niche for them. But I suspect that many interesting findings will still require the combination of data mining and wet experiments to provide key pieces of data not already available in public databases. In this regard, labs that can do both data mining and wet experiments can have an advantage over labs that can only do data mining. (Gene Expression, 2006)

Lab work will probably have to be offshored, not because it's cheaper to do elsewhere but because the "free world" is no longer the best place for unimpeded scientific inquiry.  A Hong Kong team is conducting a large-scale investigation into the genetics of intelligence, and nothing comparable is being done in either North America or Western Europe. Cost isn't the reason.

A few suggestions for research:

 

Human variation in IQ-enhancing alleles

We know that human intellectual capacity has risen through small incremental changes at very many genes, probably hundreds if not thousands. Have these changes been the same in all populations?

Davide Piffer (2013) has tried to answer this question by using a small subset of these genes. He began with seven SNPs whose different alleles are associated with differences in performance on PISA or IQ tests. Then, for fifty human populations, he looked up the prevalence of each allele that seems to increase performance. Finally, for each population, he calculated the average prevalence of these alleles at all seven genes.

The average prevalence was 39% among East Asians, 36% among Europeans, 32% among Amerindians, 24% among Melanesians and Papuan-New Guineans, and 16% among sub-Saharan Africans. The lowest scores were among San Bushmen (6%) and Mbuti Pygmies (5%). A related finding is that all but one of the alleles are specific to humans and not shared with ancestral primates.

Yes, he was using a small subset of genes that influence intellectual capacity. But you don't need a big number to get the big picture. If you dip your hand into a barrel of differently colored jelly beans, the colors you see in your hand will match well enough what's in the barrel. In any case, if the same trend holds up with a subset of 50 or so genes, it will be hard to say it's all due to chance.

 

Interaction between age and intellectual capacity

These population differences seem to widen after puberty, as Franz Boas noted a century ago (Boas, 1974, p. 234). It may be that general intelligence was largely confined to early childhood in ancestral humans, as a means to integrate information during the time of life when children become familiar with their surroundings. With increasing age, and familiarity, this learning capacity would shut down. When modern humans began to enter environments that had higher cognitive demands, natural selection may have favored retention of general intelligence in adulthood, just as it favored retention of the capacity to digest lactose wherever adults raised dairy cattle and drank milk.

After doing a principal component analysis on covariance between the above IQ-enhancing alleles and performance on IQ and Pisa tests, Piffer (2013) was able to identify three alleles that show the highest loading on the first component. Ward et al. (2014) have found that possession of these three alleles correlates with educational performance of 13 to 14 year old children. We now have a tool to measure the interaction between genes and age in the development of intellectual capacity, particularly during the critical period extending from pre-puberty to early adulthood.

 

Convergent evolution

Some human populations seem to have arrived at similar outcomes through different evolutionary trajectories. East Asians, for instance, resemble Western Europeans in their level of societal development, but this similar outcome has been achieved through a different mental and behavioral package, specifically lower levels of guilt and empathy with correspondingly higher levels of shame and prosocial behavior. In short, East Asians tend to enforce social rules more by external mediation (e.g., shaming, peer pressure, family discipline) than by internal control (e.g., guilt, empathy).

This difference probably reflects a mix of learned and innate predispositions, since natural selection favors whatever works, regardless of how hardwired it may or may not be. To the extent that these predispositions are hardwired, East Asians may be less able to cope with the sort of aloneness, anonymity, and individualism we take for granted.

It would be easy enough to study the neurological effects of social isolation on East Asians, and there is already suggestive evidence that such effects include unusual outbursts of psychotic behavior. It would be harder, however, to determine whether this malfunctioning has a heritable component.

 

Microcephalin - Why does its Eurasian allele increase brain volume?

Almost a decade ago, Bruce Lahn was among those who discovered that a gene involved in brain growth, Microcephalin, continued to evolve after modern humans had spread out of Africa. Its most recent allele arose some 37,000 years ago in Eurasia and is still largely confined to native Eurasians and Amerindians (Evans et al., 2005). Interest in this finding evaporated when no significant correlation was found between the Eurasian allele and higher scores on IQ tests (Mekel-Bobrov et al, 2007; Rushton et al., 2007). Nonetheless, a later study showed that this allele correlates with increased brain volume (Montgomery and Mundy, 2010).

The time of origin corresponds to the entry of modern humans into seasonal temperate environments. It also corresponds to the beginnings of Upper Paleolithic art—realistic 3D representations of game animals on stone, clay, bone, and ivory. The common denominator seems to be an increased capacity to store spatiotemporal information, i.e., the ability to imagine objects, particularly game animals, and how they move over space and time. If IQ tests fail to measure this capacity, it may be worthwhile to test carriers of this allele for artistic or map-reading skills.

 

ASPM - Does the Middle Eastern/West Eurasian allele assist processing of alphabetical script?

ASPM is another gene that regulates brain growth, and like Microcephalin it continued to evolve after modern humans had spread out of Africa, its latest allele arising about 6000 years ago somewhere in the Middle East. The new allele then proliferated within and outside this region, reaching higher incidences in the Middle East (37-52%) and in Europe (38-50%) than in East Asia (0-25%). Despite its apparent selective advantage, this allele does not seem to improve cognitive performance on standard IQ tests. On the other hand, there is evidence that it is associated with increased brain size (Montgomery and Mundy, 2010).

At present, we can only say that it probably assists performance on a task that exhibited the same geographic expansion from a Middle Eastern origin roughly 6000 years ago. The closest match seems to be the invention of alphabetical writing, specifically the task of transcribing speech and copying texts into alphabetical script. Though more easily learned than ideographs, alphabetical characters place higher demands on mental processing, especially under premodern conditions (continuous text with little or no punctuation, real-time stenography, absence of automated assistance for publishing or copying, etc.). This task was largely delegated to scribes of various sorts who enjoyed privileged status and probably superior reproductive success. Such individuals may have served as vectors for spreading the new ASPM allele (Frost, 2008; Frost, 2011).

 

Tay Sachs and IQ

Ashkenazi Jews have high incidences of certain neurological conditions, particularly Tay Sachs, Gaucher's disease, and Niemann-Pick disease. In the homozygous state these conditions are deleterious, but in the heterozygous state they may improve intellectual capacity by increasing neural axis length and branching. Cochran et al. (2006) argue that this improvement could amount to about 5 IQ points.

There was in fact a study in the 1980s to determine whether Tay-Sachs heterozygotes suffer from mental deficits (Kohn et al., 1988). The authors found no deficits but did not elaborate on whether performance was above-normal on the neuropsychological tests. They did mention that about two thirds of the Tay-Sachs heterozygotes had education beyond high school.

The raw data seem to be long gone, but it would not be difficult to repeat the study with a view to studying above-normal mental performance in heterozygotes and non-carriers.

 

References

Boas, F. (1974). A Franz Boas Reader. The Shaping of American Anthropology, 1883-1911, G.W. Stocking Jr. (ed.), Chicago: The University of Chicago Press. 

Cochran, G., J. Hardy, and H. Harpending. (2006). Natural history of Ashkenazi intelligence, Journal of Biosocial Science, 38, 659-693.

http://harpending.humanevo.utah.edu/trial.link/Ashkenazi.pdf  

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 

Frost, P. (2008). The spread of alphabetical writing may have favored the latest variant of the ASPM gene, Medical Hypotheses, 70, 17-20.

http://www.sciencedirect.com/science/article/pii/S0306987707003234

Frost, P. (2011). Human nature or human natures? Futures, 43, 740-748. http://dx.doi.org/10.1016/j.futures.2011.05.017  

Gene Expression. (2006). 10 Questions for Bruce Lahn.

http://www.gnxp.com/blog/2006/10/10-questions-for-bruce-lahn_10.php

Kohn, H., P. Manowitz, M. Miller, and A. Kling. (1988). Neuropsychological deficits in obligatory heterozygotes for metachromatic leukodystrophy, Human Genetics, 79, 8-12. 

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 

Piffer, D. (2013). Factor analysis of population allele frequencies as a simple, novel method of detecting signals of recent polygenic selection: The example of educational attainment and IQ, Mankind Quarterly, 54, 168-200.

http://emilkirkegaard.dk/en/wp-content/uploads/Factor-Analysis-of-Population-Allele-Frequencies-as-a-Simple-Novel-Method-of-Detecting-Signals-of-Recent-Polygenic-Selection-The-Example-of-Educational-Attainment-and-IQ.pdf  

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  

Ward, M.E., G. McMahon, B. St Pourcain, D.M. Evans, C.A. Rietveld, et al. (2014). Genetic variation associated with differential educational attainment in adults has anticipated associations with school performance in children. PLoS ONE 9(7): e100248. doi:10.1371/journal.pone.0100248

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0100248#pone-0100248-g002

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  

More on gene-culture co-evolution

According to the online magazine Seed, “a growing number of scientists argue that human culture itself has become the foremost agent of biological change.” Much of this change has been surprisingly recent:

In the DNA of a group of 5,000-year-old skeletons from Germany, they discovered no trace of the lactase allele, even though it had originated a good 3,000 years beforehand. Similar tests done on 3,000-year-old skeletons from Ukraine showed a 30 percent frequency of the allele. In the modern populations of both locales, the frequency is around 90 percent.

I thought I was on top of the literature, but this was new to me. It’s even more proof that human evolution did not stop with the advent of Homo sapiens. It has continued … even after the transition from prehistory to history!

The same article also has some thoughts from Bruce Lahn, the evolutionary geneticist who has mapped human variation at two genes, ASPM and microcephalin, that seem to regulate the growth of brain tissue.

Even if Lahn could prove to everyone's satisfaction that ASPM and microcephalin are under selection, whether intelligence is the trait being selected for would be far from a settled question. It could be, as Lahn suggested, that some other mental trait is being selected, or that the activity of ASPM and microcephalin in other parts of the body is what is under selection. More work will certainly be done. But one can speculate with far more confidence about what drove the dramatic increase in intelligence attested by the fossil record: the advent of human culture.

"Intelligence builds on top of intelligence," says Lahn. "[Culture] creates a stringent selection regime for enhanced intelligence. This is a positive feedback loop, I would think." Increasing intelligence increases the complexity of culture, which pressures intelligence levels to rise, which creates a more complex culture, and so on. Culture is not an escape from conditioning environments. It is an environment of a different kind.

Reference

Phelan, B. (2008). How we evolve. A growing number of scientists argue that human culture itself has become the foremost agent of biological change. Seed Posted October 7, 2008