How modular is intelligence?

Great at reading or recognizing faces? You might not do so well on an IQ test. Source: Histoire naturelle générale et particulière avec la Description du Cabinet du Roy (1749) (Wikicommons)

 

The English psychologist Charles Spearman was the first to argue that a single factor, called "g," explains most of the variability in human intelligence. When observing the performance of children at school, he noticed that a child who did well in math would also do well in geography or Latin. There seemed to be a general factor that facilitates almost any kind of mental task.

Spearman did, however, acknowledge the existence of other factors that seem more task-specific:

[...] all branches of intellectual activity have in common one fundamental function (or group of functions), whereas the remaining or specific elements of the activity seem in every case to be wholly different from that in all the others. (Spearman, 1904, p. 284)

 

That is where things stood for over a century. In recent years, however, we’ve begun to identify the actual genes that contribute to intelligence. These genes are very numerous, numbering perhaps in the thousands, with each one exerting only a small effect. Many act broadly on intelligence in general and may correspond to the g factor, which seems to be a widespread property of neural tissue, perhaps cortical thickness or the integrity of white matter in the brain. Other genes act more narrowly on specific mental tasks. The ability to recognize faces, for instance, seems to have no relation at all to general intelligence. You can be great at recognizing faces while being as dumb as rocks (Zhu et al., 2009).

One way to locate these genes is through genome-wide association studies. We look at the various alleles of genes whose locations are already known, typically SNPs (single nucleotide polymorphisms), and see whether this source of variability correlates with variability in a mental trait. If we find a significant correlation, the genes for that trait must be nearby. The same kind of study can also show us how narrowly or broadly these genes act. Do they merely influence intelligence in general? Or do they provide more specific instructions? Such as how to recognize certain objects or how to react to them?

A genome-wide association study has recently shed light on various mental traits. In most cases, a common factor seems to explain about half of the genetic variability. This common factor is weakest for emotion identification, i.e., the ability to identify the emotions of other people by their facial expressions. Emotion identification actually correlates negatively with nonverbal reasoning (-0.25) and only weakly with verbal memory (0.17) and spatial reasoning (0.26). The highest correlation is with reading (0.40) and language reasoning. (0.45). Reading and language reasoning are highly intercorrelated, perhaps because they share the same mental module (Robinson et al., 2014).

This partial modularity has been confirmed by a recent twin study on reading and math ability. If we look at the genetic component of either reading or math ability, at least 10% and probably half affects performance on both tasks. Conversely, the other half is specific to either one or the other (Davis et al., 2014).

 

An evolutionary mystery?

But how can reading ability have a specific genetic basis if people began to read only in historic times? Indeed, history is said to begin with the first written documents. Surely humans weren't still evolving at that point?

To ask the question is to answer it. Not only were they still evolving, they were actually doing so at a faster pace than their prehistoric ancestors. Humans have undergone much more genetic change over the past 10,000 years than over the previous 100,000 (Hawks et al., 2007). This is a difficult fact to swallow, let alone digest, but we must learn to accept it and all of its implications.

The new findings on reading ability are consistent with other ones. The human brain has a special region, called the Visual Word Form Area, that is used to recognize written words and letters. If it is damaged, your reading ability will suffer but not your recognition of objects, names, faces, or general language abilities. There will be some improvement over the next six months, but reading will still take twice as long as it had previously. This brain region varies in size and organization from one individual to another and from one human population to another, being differently organized in Chinese people than in Europeans (Frost, 2014; Gaillard et al, 2006; Glezer and Riesenhuber, 2013; Levy et al., 2013; Liu et al., 2008).

Genome-wide association studies may help us pinpoint the actual genes responsible for the Visual Word Form Area. In fact, we may have already found one: ASPM. This gene influences brain growth in other primates and has evolved in humans right up into historic times. Its latest allele arose about 6000 years ago in the Middle East and proliferated until it reached incidences of 37-52% in Middle Easterners, 38-50% in Europeans, and 0-25% in East Asians. Despite its apparent selective advantage, this allele does not improve performance on IQ tests (Mekel-Bobrov et al.,2007; Rushton et al., 2007). It is nonetheless associated with larger brain size in humans (Montgomery and Mundy, 2010).

Its Middle Eastern origin some 6000 years ago suggests this allele may have owed its success to the invention of writing. Most people had trouble reading, writing, and copying lengthy texts in ancient times, when characters were written continuously with little or no punctuation. There was an acute need for scribes who could excel at this task, and such people were rewarded with reproductive success (Frost, 2008; Frost, 2011).

 

Conclusion

Human intelligence is modular to varying degrees, and much of this modularity seems to have arisen during historic times. It is a product of humans adapting not only to their physical environments but also to their more rapidly evolving cultural environments.

While there is such a thing as general intelligence, it seems to be only half of the picture. Two people may have the same IQ and yet differ significantly in various mental abilities. There may also be trade-offs between general intelligence and more specific mental tasks. If you're great at abstract reasoning, you may be lousy at decoding facial expressions. This may be because the two abilities compete with each other for limited mental resources. Or it may be that selection for abstract reasoning has occurred in an environment where people can trust each other and have no need to scrutinize facial expressions for signs of lying ... or imminent physical assault.

 

The same applies to human populations. Two populations may have the same mean IQ, and yet differ statistically over a large number of mental and behavioral traits. Although these differences may be scarcely noticeable if we compare two individuals taken at random from each population, their accumulative effect over many thousands of individuals can steer one population along one path of cultural evolution and the other along another. Furthermore, two populations may arrive at a similar outcome via different paths of cultural evolution and via different mental and behavioral packages. Europeans and East Asians have both reached an advanced level of societal development, but this similar outcome has been achieved in East Asian societies largely through external mediation of rule enforcement (e.g., shaming, peer pressure, family discipline) and in European ones mainly through internal means of control (e.g., guilt, empathy).

 

References

 

Davis, O.S.P., G. Band, M. Pirinen, C.M.A. Haworth, E.L. Meaburn, Y. Kovas, N. Harlaar, et al. (2014). The correlation between reading and mathematics ability at age twelve has a substantial genetic component, Nature Communications, 5

http://www.nature.com/ncomms/2014/140708/ncomms5204/full/ncomms5204.html

 

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 

 

Frost, P. (2014). The paradox of the Visual Word Form Area, March 1, Evo and Proud

http://evoandproud.blogspot.ca/2014/03/the-paradox-of-visual-word-form-area.html

 

Gaillard, R., Naccache, L., P. Pinel, S. Clémenceau, E. Volle, D. Hasboun, S. Dupont, M. Baulac, S. Dehaene, C. Adam, and L. Cohen. (2006). Direct intracranial, fMRI, and lesion evidence for the causal role of left inferotemporal cortex in reading, Neuron, 50, 191-204.

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.76.7620&rep=rep1&type=pdf  

Glezer, L.S. and M. Riesenhuber. (2013). Individual variability in location impacts orthographic selectivity in the "Visual Word Form Area", The Journal of Neuroscience, 33(27), 11221-11226.

http://www.jneurosci.org/content/33/27/11221.full

 

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.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2410101/

 

Levy, J., J.R Vidal, R. Oostenveld, I. FitzPatrick, J-F. Démonet, and P. Fries. (2013). Alpha-band suppression in the Visual Word Form Area as a functional bottleneck to consciousness, NeuroImage, 78C, 33-45.

http://hal.inria.fr/docs/00/81/96/67/PDF/Levy_et_al.pdf

 

Liu, C., W-T. Zhang, Y-Y Tang, X-Q. Mai, H-C. Chen, T. Tardif, and Y-J. Luo. (2008). The visual word form area: evidence from an fMRI study of implicit processing of Chinese characters, NeuroImage, 40, 1350-1361.

http://www.yi-yuan.net/english/PAPERS/PAPERS_2008/2008_The-Visual-Word-Form-Area-Evidence.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 

 

Robinson, E.B., A. Kirby, K. Ruparel, J. Yang, L. McGrath, V. Anttila, B.M. Neale, K. Merikangas, T. Lehner, P.M.A. Sleiman, M.J. Daly, R. Gur, R. Gur and H. Hakonarson. (2014). The genetic architecture of pediatric cognitive abilities in the Philadelphia Neurodevelopmental Cohort, Molecular Psychiatry, published online July 15

http://www.nature.com/mp/journal/vaop/ncurrent/full/mp201465a.html

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

Spearman, C. (1904). "General intelligence," objectively determined and measured, The American Journal of Psychology, 15, 201-292.

http://www.jstor.org/stable/1412107

Zhu, Q., Song, Y., Hu, S., Li, X., Tian, M., Zhen, Z., Dong, Q., Kanwisher, N. and Liu, J. (2009). Heritability of the specific cognitive ability of face perception, Current Biology, 20, 137-142.

http://web.mit.edu/bcs/nklab/media/pdfs/Zhu_et_al_Heritability.pdf

The Visual Word Form Area

Codex Suprasliensis (source). Texts were less reader-friendly in the past. An ability to read and write meant not only a good livelihood but also reproductive success.

 

The Visual Word Form Area (VWFA) is a brain region that specializes in recognizing written words and letters. Though not essential to reading and writing, it makes these tasks much easier. It plays no role in other mental tasks, as shown when a case of epilepsy was treated by a surgical lesion to the VWFA:

[…] our patient presented a clear-cut reading impairment following surgery, while his performance remained flawless in object recognition and naming, face processing, and general language abilities. (Gaillard et al, 2006).

Some improvement was observed six months afterwards, but reading still took twice as long as it had before surgery.

The VWFA seems to function differently in different human populations, particularly between users of alphabetical script, where symbols represent sounds, and users of logographic script, where symbols represent ideas. Chinese subjects, for instance, process their idea-based symbols with assistance from other brain regions, whereas Westerners process their sound-based symbols only in the VWFA (Liu et al., 2008). Similarly, dyslexics activate this brain region in ways that differ by linguistic background, apparently because of differences in spelling and writing (Paulesu et al., 2001).

Evolutionarily speaking, these population differences seem paradoxical, as does the very existence of the VWFA. As Dehaene and Cohen (2011) note, natural selection could not have created a specialized mental organ for reading because “the invention of writing is too recent and, until the last century, concerned too small a fraction of humanity to have influenced the human genome.” Writing emerged in the Middle East only six thousand years ago, and some societies adopted writing only within the past century. Even in societies that have long been literate, reading and writing were confined to a minority until recent times.

To resolve this paradox, Dehaene and Cohen (2011) argue that our brains deal with word recognition by recycling neurons that were originally meant for face recognition:

Thus, learning to read must involve a ‘neuronal recycling’ process whereby pre-existing cortical systems are harnessed for the novel task of recognizing written words. […] reading acquisition should ‘encroach’ on particular areas of the cortex – those that possess the appropriate receptive fields to recognize the small contrasted shapes that are used as characters, and the appropriate connections to send this information to temporal lobe language areas. […] We have proposed that writing evolved as a recycling of the ventral visual cortex’s competence for extracting configurations of object contours (Dehaene & Cohen, 2011)

For Dehaene and Cohen, the VWFA is not hardwired in our genes. It always takes up the same area of the brain because that is where we can most easily recruit neurons when learning to recognize words. But why then does this recruitment happen so fast in young children and illiterate adults? A study on kindergarten children found that their VWFAs preferentially responded to pictures of letter strings after the subjects had played a grapheme/phoneme correspondence game for a total of 3.6 hours over an 8-week period. This finding is all the more strange because only a few of the children could actually read, and even then only at a rudimentary level (Brem et al., 2010; Dehaene et al., 2010).

So are we born with a ready-to-activate VWFA? And has this mental organ evolved out of an assortment of face-recognition neurons through generations of natural selection? But we’re now back to our evolutionary paradox. How could the VWFA have arisen in no more than six thousand years? The time constraint seems all the more paradoxical if we remember that literacy was confined until recent times to a privileged minority.

But maybe the paradox is only apparent. First, we estimate the literacy rate of past societies from signed documents of one sort or another: wills, court depositions, marriage certificates, etc. (Barr & Kamil, 1996, p. 52). If the “signature” is an ‘X’, the person is deemed to have been illiterate. We can thus measure the admittedly small proportion of people who could read and write cursive script. But a larger proportion could read and write texts of block letters, and even more could read short texts of block letters, e.g., storefront signs and graffiti, while not being able to write. Current historical methods thus underestimate the total proportion of people who had some reading ability.

Second, as Clark (2007) has shown, a selection pressure can affect an entire population even though it acts only on a minority of better-off individuals. As late as the 19th century, the English lower class did not replace itself demographically and was continually replenished by downwardly mobile individuals from the middle and upper classes. The average English man or woman, however poor, was largely descended from yesteryear’s kings, merchants, and scribes.

Finally, new mental organs can arise through natural selection over a fairly short time, especially if they evolve out of pre-existing structures. As Henry Harpending and Gregory Cochran point out:

Even if 40 or 50 thousand years were too short a time for the evolutionary development of a truly new and highly complex mental adaptation, which is by no means certain, it is certainly long enough for some groups to lose such an adaptation, for some groups to develop a highly exaggerated version of an adaptation, or for changes in the triggers or timing of that adaptation to evolve. That is what we see in domesticated dogs, for example, who have entirely lost certain key behavioral adaptations of wolves such as paternal investment. Other wolf behaviors have been exaggerated or distorted (Harpending & Cochran, 2002)

So who needs a VWFA?

Still, is the VWFA really vital to survival? Is it something that natural selection could have favored? As our epileptic patient showed, one can read without a functioning VWFA—admittedly at only half the normal speed.

Keep in mind that texts were a lot less reader-friendly in the past. Because parchment was expensive, writing usually took the form of a continuous stream of characters with little or no punctuation. It was a rare person who could read and write such texts on a sustained basis, so it is no surprise that scribes enjoyed not only good livelihoods but also reproductive success. According to the Book of Sirach [39: 11], “If [a scribe] lives long, he will leave a name greater than a thousand” (Frost, 2011).

When people began to read and write some six thousand years ago, they made use of neurons and neural networks that had served other purposes. It was a make-do solution that nonetheless paved the way for later improvements. If you had a knack for reading and writing, you now had an edge over those who did not, and that knack would be better represented in the next generation. Such mental characteristics would have become more and more widespread with the growing need for people who could process large volumes of textual information on a daily basis.

In this, as in many other ways, humans have directed their own evolution. After creating a new behavior by pushing their envelope of phenotypic plasticity, they gradually acquire a genetic basis for the new phenotype through natural selection for genetic characteristics that make it work better. Humans shape their cultural environment, and this cultural environment in turn shapes humans.

Indeed, there is a suspicious resemblance between the spread of alphabetical writing and the spread of the most recent variant of ASPM, a gene implicated in the regulation of primate brain growth. In humans, a new variant arose some six thousand years ago, apparently somewhere in the Middle East. It then spread outward, becoming more prevalent in the Middle East (37-52% incidence) and Europe (38-50%) than in East Asia (0-25%) (Frost, 2011; Mekel-Bobrov et al., 2005).

References

Barr, R. & M.L. Kamil. (1996). Handbook of Reading Research vol. 2, Routledge.

Brem, S., S. Bach, K. Kucian, T.K. Guttorm, E. Martin, H. Lyytinen, D. Brandeis, & U. Richardson. (2010). Brain sensitivity to print emerges when children learn letter-speech sound correspondences, Proceedings of the National Academy of Sciences U.S.A., 107, 7939–7944.

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

Dehaene, S. & L. Cohen. (2011). The unique role of the visual word form area in reading, Trends in Cognitive Sciences, 15, 254-262.

Dehaene, S. et al. (2010) How learning to read changes the cortical networks for vision and language, Science, 330, 1359–1364.

Frost, P. (2011). Human nature or human natures? Futures, 43, 740-748.

http://dx.doi.org/10.1016/j.futures.2011.05.017

Gaillard, R., Naccache, L., P. Pinel, S. Clémenceau, E. Volle, D. Hasboun, S. Dupont, M. Baulac, S. Dehaene, C. Adam, & L. Cohen. (2006). Direct intracranial, fMRI, and lesion evidence for the causal role of left inferotemporal cortex in reading. Neuron, 50, 191-204.

Harpending, H., & G. Cochran. (2002). In our genes, Proceedings of the National Academy of Sciences U.S.A., 99(1), 10-12.

Liu, C., W-T. Zhang, Y-Y Tang, X-Q. Mai, H-C. Chen, T. Tardif, & Y-J. Luo. (2008). The visual word form area: evidence from an fMRI study of implicit processing of Chinese characters. NeuroImage, 40, 1350-1361.

Mekel-Bobrov, N., S.L. Gilbert, P.D. Evans, E.J. Vallender, J.R. Anderson, R.R. Hudson, S.A. Tishkoff, & B.T. Lahn. (2005). Ongoing adaptive evolution of ASPM, a brain size determinant in Homo sapiens, Science, 309, 1720-1722.

Paulesu E., J.F. Démonet, F. Fazio, E. McCrory, V. Chanoine, N. Brunswick et al (2001). Dyslexia: cultural diversity and biological unity, Science, 291, 2165–2167.

Review of 2010

Drinking from the wrong chalice? By his mid-40s, Michael Jackson had skin like parchment.

The end of 2010 is drawing nigh, and the time has come to review my predictions from last year.

Brain growth genes

Back in 2005, it was found that human populations vary considerably at two genes, ASPM and microcephalin, that control the growth of brain tissue. The finding seemed to be ‘huge’ in its implications. Then, it all fizzled out. No correlation could be found between variation at either gene and differences in mental ability or head circumference (Mekel-Bobrov et al., 2007; Rushton et al., 2007).

A recent study has now shown that ASPM and several other genes (MCPH1, CDK5RAP2, CENPJ) do in fact influence growth of brain tissue, specifically cortical tissue.

… In 2010, we’ll probably see further developments in this area. Stay tuned.

This year did see further developments. Interestingly, these gene loci seem to interact with sex and ethnicity in their effects:

[In a Norwegian study by Rimol et al.] for each of the 15 positive SNPs, the association was sex-specific with all significant results for CDK5RAP2 SNPs being found only in males, whilst the significant results for MCPH1 and ASPM were only found in females.

The second study, by Wang et al., only considered variation in the coding sequence of MCPH1 but found that one non-synonymous SNP is associated with male cranial volume but not female cranial volume in a Chinese population of nearly 900 individuals, supporting a role for sex in the action of microcephaly genes. Intriguingly, it also suggests that SNPs in the same locus can have opposite effects in males and females, as for MCPH1 an exonic SNP contributes to Chinese male cranial volume whilst intronic SNPs and SNPs downstream of the coding sequence are associated with Norwegian female brain size. As the authors discuss, these results strongly suggest some microcephaly variants may influence brain development dependent on hormonal background or through interactions with genes which are differentially expressed between the sexes, potentially contributing to sex specific differences in brain structure. (Montgomery & Mundy 2010)

But why did earlier studies find nothing?

First, many of the previous studies only tested for associations with the few, recently derived ASPM and MCPH1 haplotypes which were the focus of claims of recent positive selection, while both Rimol et al. and Wang et al. consider a larger number of SNPs for which there is no a priori evidence for selection. Second, despite the possibility of deriving clear hypotheses of what phenotypes these loci should affect, many previous studies examined traits that are, at best, not directly relevant (e.g. IQ or altruism) or quite distantly removed (e.g. adult head circumference). (Montgomery & Mundy 2010)

Many people had thought that all variation in mental capacity shows up on IQ tests. So they threw in the towel once it became apparent that IQ does not vary with genetic variation at these loci.

So how do these loci affect mental capacity? I’ve argued that the most recent ASPM variant seems to be associated with the spread of alphabetical writing. It may thus assist the visual cortex in recognizing, storing, and processing strings of alphabetical script (Frost 2008).

Alternatively, Dediu and Ladd (2007) have argued that ASPM and microcephalin variants correlate with use or non-use of tone languages. This hypothesis has been tested with Chinese, Korean, Hmong, and American Caucasians who had little training in tone recognition, i.e., they were not musicians and did not engage in singing or instrument playing. The Chinese and Koreans consistently outperformed the other participants when asked to identify the relative distance between two tones. The Hmong showed no such advantage, even though they shared the ASPM and microcephalin characteristics of the Chinese and Koreans (Hove et al., 2010). Thus, while some East Asian populations apparently are better at processing differences in pitch, this aptitude seems to be unrelated to ASPM or microcephalin.

Early modern human genome

Scientists have retrieved mtDNA from a 30,000 year-old hunter-gatherer from Kostenki, Russia. This seems to be part of a trend to study the genome of early modern humans.

The Kostenki mtDNA genome was entirely sequenced, despite problems that seemed intractable (difficulties in distinguishing between early modern human DNA and contamination from present-day human DNA). The authors concluded: “With this approach, it may even become possible to analyze the nuclear genomes of early modern humans” (Krause et al., 2010).

This development is indeed promising. If we can compare early modern DNA with present-day nuclear DNA, we’ll find out the exact genetic changes, especially those in neural wiring, that led to the ‘big bang’ of modern human evolution some 80,000 to 60,000 years ago. Unfortunately, this ‘big bang’ almost certainly took place in Africa, where the climate is much less conducive to DNA preservation.

Ethnic differences in vitamin D metabolism

This year will see further evidence that natural selection has caused differences in metabolism among different human populations, including vitamin D metabolism.

For instance, many populations have long been established at latitudes where vitamin-D synthesis is impossible for most of the year. Some of these populations can get vitamin D from dietary sources (e.g., fatty fish) but most cannot. In these circumstances, natural selection seems to have adjusted their metabolism to reduce their vitamin-D requirements. We know that the Inuit have compensated for lower production of vitamin D by converting more of this vitamin to its most active form (Rejnmark et al., 2004). They also seem to absorb calcium more efficiently, perhaps because of a different vitamin-D receptor genotype (Sellers et al., 2003). Even outside the Arctic zone, there seem to be differences in vitamin-D metabolism from one population to another. In particular, vitamin-D levels seem to be generally lower in darker-skinned populations (Frost, 2009).

… Unfortunately, our norms for adequate vitamin intake are based on subjects or populations of European origin. We are thus diagnosing vitamin-D deficiency in non-European individuals who are, in fact, perfectly normal. This is particularly true for African Americans, nearly half of whom are classified as vitamin-D deficient, even though few show signs of calcium deficiency—which would be a logical outcome. Indeed, this population has less osteoporosis, fewer fractures, and a higher bone mineral density than do Euro-Americans, who generally produce and ingest more vitamin D (Frost, 2009).

… What will be the outcome of raising vitamin-D levels in these populations? Keep in mind that we are really talking about a hormone, not a vitamin. This hormone interacts with the chromosomes and gradually shortens their telomeres if concentrations are either too low or too high. Tuohimaa (2009) argues that optimal levels may lie in the range of 40-60 nmol/L. In non-European populations the range is probably lower. It may also be narrower in those of tropical origin, since their bodies have not adapted to the wide seasonal variation of non-tropical humans.

If this optimal range is continually exceeded, the long-term effects may look like those of aging …

I hope that people of African or Native origin will resist the vitamin-D siren song. Otherwise, many of them will become shriveled-up husks by their mid-40s … just like Michael Jackson.

Evidence continued to mount this year that vitamin-D metabolism differs by ethnicity. For risk of atherosclerosis, the optimal range is lower among African Americans than among European Americans. A sample of African Americans showed a positive correlation between calcified plaque formation and blood levels of vitamin D (25(OH)D), despite a negative correlation among European Americans over the same range (Freedman et al., 2010).

Another study of African Americans found that blood levels of 25(OH)D decreased linearly with increasing African ancestry, the decrease being 2.5-2.75 nmol/L per 10% increase in African ancestry. Sunlight and diet were 46% less effective in raising these levels among subjects with high African ancestry than among those with low/medium African ancestry (Signorello et al. 2010).

The New York Times has recently covered the growing unease with vitamin D supplements:

The very high levels of vitamin D that are often recommended by doctors and testing laboratories — and can be achieved only by taking supplements — are unnecessary and could be harmful, an expert committee says.

… The 14-member expert committee was convened by the Institute of Medicine, an independent nonprofit scientific body, at the request of the United States and Canadian governments. It was asked to examine the available data — nearly 1,000 publications — to determine how much vitamin D and calcium people were getting, how much was needed for optimal health and how much was too much.

… Some labs have started reporting levels of less than 30 nanograms of vitamin D per milliliter of blood as a deficiency. With that as a standard, 80 percent of the population would be deemed deficient of vitamin D, Dr. Rosen said. Most people need to take supplements to reach levels above 30 nanograms per milliliter, he added.

But, the committee concluded, a level of 20 to 30 nanograms [50 to 75 nmol/L] is all that is needed for bone health, and nearly everyone is in that range.

… It is not clear how or why the claims for high vitamin D levels started, medical experts say. First there were two studies, which turned out to be incorrect, that said people needed 30 nanograms of vitamin D per milliliter of blood, the upper end of what the committee says is a normal range. They were followed by articles and claims and books saying much higher levels — 40 to 50 nanograms or even higher — were needed.

After reviewing the data, the committee concluded that the evidence for the benefits of high levels of vitamin D was “inconsistent and/or conflicting and did not demonstrate causality.”

Evidence also suggests that high levels of vitamin D can increase the risks for fractures and the overall death rate and can raise the risk for other diseases. (Kolata 2010)

H/T to Tod

References

Dediu, D., and D.R. Ladd (2007). Linguistic tone is related to the population frequency of the adaptive haplogroups of two brain size genes, ASPM and Microcephalin. Proceedings of the National Academy of Sciences, 104, 10944-10949.

Freedman B.I., L.E. Wagenknecht, K.G. Hairston KG et al. (2010). Vitamin D, adiposity, and calcified atherosclerotic plaque in African-Americans. Journal of Clinical Endocrinology & Metabolism, 95, 1076-1083.

Frost, P. (2009). Black-White differences in cancer risk and the vitamin-D hypothesis, Journal of the National Medical Association, 101, 1310-1313.

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

Hove, M.J., M.E. Sutherland, and C.L. Krumhansl. (2010). Ethnicity effects in relative pitch, Psychonomic Bulletin & Review, 17, 310-316.

Kolata, G. (2010). Report Questions Need for 2 Diet Supplements, The New York Times, November 29, 2010
http://www.nytimes.com/2010/11/30/health/30vitamin.html?_r=2&hp

Krause, J., A.W. Briggs, M. Kircher, T. Maricic, N. Zwyns, A. Derevianko, and S. Pääbo. (2010). A Complete mtDNA genome of an early modern human from Kostenki, Russia, Current Biology 20, 231–236.

Mekel-Bobrov, N., Posthuma D., Gilbert S.L., et al. (2007). The ongoing adaptive evolution of ASPM and Microcephalin is not explained by increased intelligence. Hum Mole Genet, 16, 600–8.

Montgomery, S.H. and N.I. Mundy. (2010). Brain Evolution : Microcephaly genes weigh in, Current Biology, 20(5), R244

Rejnmark L, Jørgensen ME, Pedersen MB, et al. (2004). Vitamin D insufficiency in Greenlanders on a Westernized fare: ethnic differences in calcitropic hormones between Greenlanders and Danes, Calcif Tissue Int, 74, 255-263.

Rimol, L.M., I. Agartz, S. Djurovic, A.A. Brown, J.C. Roddey, A.K. Kähler, M. Mattingsdal, L. Athanasiu, A.H. Joyner, N.J. Schork, et al. for the Alzheimer’s Disease Neuroimaging Initiative (2010). Sex-dependent association of common variants of microcephaly genes with brain structure. Proceedings of the National Academy of Science. USA, 107, 384–388.

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Ancient reading and writing

The French journal L’Histoire has a special issue on reading and writing in ancient societies. One article, about Mesopotamia, makes several points that support an argument I have made: the invention of writing, especially alphabetical writing, created a strong selection pressure for people who had the rare ability to take dictation or copy written texts with a low error rate and over extended lengths of time (Frost, 2007).

1. In the ancient world, reading and writing required much stamina, concentration, and memorization, more than is the case today with current reader-friendly language. This may be seen in the long training needed to make a good scribe.

To learn cuneiform writing, the students followed a specific and very standardized curriculum that has been reconstituted thanks to the thousands of exercises that have been found. Training began with writing of simple signs and then writing of lists of syllables and names. Next came copying of long lexical lists that corresponded to all sorts of realities: names of trades, animals, plants, vases, wooden objects, fabrics, … Then came copying of complex Sumerian ideograms, even though Sumerian had become a dead language, with their pronunciation and their translation in Akkadian. Learning of Sumerian was completed by copying increasingly difficult texts: proverbs and contracts, and then hymns.

2. Scribes were not recruited from the general population. Their profession seems to have been largely family-transmitted, and was recognized as such.

Learning of cuneiform, in the early 2nd millennium, took place in a master’s home and not in an institutional “school”. The tradition was often passed down within families, with scribes training their children.

3. Although writing was generally done by scribes, many more people could read and, if need be, write.

It has long been believed that in ancient Mesopotamia only a very small part of the population knew how to read and write and that these skills were reserved for specialists, i.e., scribes. Several recent studies have called this idea into question and have shown that access to reading, and even writing, was not so uncommon. Some kings, and also the members of their entourage, family, ministers, or generals, as well as merchants, could do without a reader’s services, when necessary, and decipher on their own the letters sent to them. Sometimes, they were even able to take a quill—the sharpened end of a reed—and write their own tablets.

The last point may help us understand a chicken-and-egg question. If reading and writing are associated with specific genetic predispositions, how did people initially manage to read and write? (see previous posts: Decoding ASPM: Part I, Part II, Part III)

The answer is that these predispositions are not necessary for reading and writing. But they do help. Specifically, they help the brain process written characters faster. In this way, natural selection has genetically reinforced an ability that started as a purely cultural innovation.

This may be a recurring pattern in human evolution. Humans initially took on new tasks, like reading and writing, by pushing the envelope of mental plasticity. Then, once these tasks had become established and sufficiently widespread, natural selection favored those individuals who were genetically predisposed to do them better.

The term is ‘gene-culture co-evolution’ and it’s still a novel concept. Until recently, anthropologists thought that human cultural evolution had simply taken over from human genetic evolution, making the latter unnecessary and limiting it to superficial ‘skin-deep’ changes. But recent findings now paint a different picture. Genetic evolution has actually accelerated in our species over the past 40,000 years, and even more over the past 10,000-15,000. The advent of agriculture saw the rate increase a 100-fold. In all, natural selection has changed at least 7% of the genome during the existence of Homo sapiens. (Hawks et al., 2007; see previous post). And this is a minimal estimate that excludes much variation that may or may not be due to selection. The real figure could be higher. Much higher.

References

Frost, P. 2007. "The spread of alphabetical writing may have favored the latest variant of the ASPM gene", Medical Hypotheses, 70, 17-20.

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(52), 20753-20758

Lion, B. (2008). Les femmes scribes de Mésopotamie. L’Histoire, no. 334 (septembre), pp. 46-49.