A second look at ASPM

Worldwide frequency of the new ASPM variant (Mekel-Bobrov et al. 2007)



Fifteen years ago, Science published a major finding: the human brain was still evolving well after the dawn of history. This could be seen in the evolution of ASPM, a gene that severely reduces brain size if it fails to function during development.

Here, we show that one genetic variant of ASPM in humans arose merely about 5800 years ago and has since swept to high frequency under strong positive selection. These findings, especially the remarkably young age of the positively selected variant, suggest that the human brain is still undergoing rapid adaptive evolution. (Mekel-Bobrov et al. 2007)

This variant seems to have come from the Middle East, where it is most prevalent today (37-52%). Its prevalence is next highest in Europe (38-50%). It is much less common in East Asia (0-25%) and virtually absent almost everywhere else.

Interest waned in the subject when several researchers found no association between the new variant and IQ scores or brain size (Mekel-Bobrov et al. 2007; Rushton et al. 2007). At the time it was widely thought, notably by J. Philippe Rushton, that IQ covers all aspects of mental effort. When I asked him whether the researchers had measured mental endurance, he replied: "No, they just used the standard IQ tests, head circumference, and (in our case) a test of altruism. [...] Generally there isn't thought to be much left to be explained after g is taken out."

This view has since been called into question. Some cognitive abilities correlate poorly with IQ, like executive function (Arffa 2007). Others show no correlation at all, like face recognition (Zhu et al. 2010). Furthermore, there has been growing evidence that the different ASPM variants of modern humans affect only some parts of the brain, and not the entire brain. According to a comparative study of primate species, the evolution of ASPM does not correlate with major changes in the whole brain or in cerebellum size: 

Particularly striking is the result that only major changes of cerebral cortex size and not major changes in whole brain or cerebellum size are associated with positive selection in ASPM. This is consistent with an expression report indicating that ASPM's expression is limited to the cerebral cortex of the brain (Bond et al. 2002). Our findings stand in contrast to recent null findings correlating ASPM genotypes with human brain size variation. Those studies used the relatively imprecise phenotypic trait of whole brain instead of cerebral cortex size (Rushton, Vernon, and Bons 2006; Woods et al. 2006; Thimpson et al. 2007). Although previous studies have shown that parts of the brain scale strongly with one another and especially with whole brain (e.g., Finlay and Darlington 1995), evidence here suggests that different brain parts still have their own evolutionary and functional differentiation with unique genetic bases. (Ali and Meier 2008)

Another comparative study found that ASPM had undergone accelerated change in chimpanzee, bonobo, and human lineages. Perhaps more interestingly, the effects were confined to development of the cerebral cortex:

Our findings indicate that ASPM variation is potentially associated with cerebral ventricular volume in chimpanzees, but not with any of the other brain structure measures. Ventricles are a critical site of neuronal proliferation in early development. Furthermore, the cerebrospinal fluid which circulates through the ventricles throughout life carries proteins that play important roles in central nervous system development and maintenance, like Sonic Hedgehog protein and Insulin-like Growth Factor 2.

Sonic Hedgehog protein?

Thus, variation in ventricular volume may affect the circulation of growth factors that could potentially influence the regulation of cerebral cortical development. Alternatively, because ASPM has a significant effect on neural progenitor cycling along the ventricles in fetal life, the association shown in our study may be a result of how brain size is patterned by ASPM during neurogenesis in early development. It has been shown that ASPM plays a role in regulating the affinity of ventricular radial glial cells (VRGs) for the ventricular surface. (Singh et al. 2019)

While there is also a broader role in brain development and brain size, it is usually limited to extreme cases, like microcephaly:

The abundance of ASPM mutations in human patients with microcephaly suggests that the gene plays a significant role in the regulation of brain size; however, variation in the gene has not always shown direct impact on brain circumference, volume, and intelligence in non-pathological populations. It is possible that ASPM interacts with other genes to affect brain volume, and thus associations depend on genetic background. Furthermore, selective pressure on ASPM may be associated with other aspects of neuronal function that do not lead to overt changes in brain structure, or might have a pleiotropic effect in other areas of the body, as ASPM is also expressed outside of the brain (Singh et al. 2019)

Possible explanations for the new ASPM variant

Shift from tonal to nontonal language?

So what made the new ASPM variant so successful? Two British researchers, Dan Dediu and D. Robert Ladd argue that it was a shift from tonal to non-tonal language. After showing that nontonality correlates geographically with the new ASPM variant (and also a new variant of the Microcephalin gene), they note that "the fact that nontonality is associated with the derived haplogroups suggests that tone is phylogenetically older and that the bias favors nontonality" (Dediu Ladd 2007).

If this is true, tonality gave way to nontonality in the Middle East when the new ASPM variant arose there some six thousand years ago. Yet we have no evidence of such a shift. Furthermore, languages have usually evolved from nontonality to tonality: "it seems to be the dominant view in the literature that tones arose from a toneless state" (Abramson 2004).

Spread of alphabetical writing?

I have argued for another explanation: the new ASPM variant was successful because it somehow assisted a mental task that originated in the Middle East some six thousand years ago and then spread into Europe. The task was alphabetical writing, specifically the mental process of transcribing speech and copying texts into alphabetical characters. Though more easily learned than ideographs, these characters place higher demands on the mind, 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 assigned to scribes of various sorts who enjoyed privileged status and probably superior reproductive success, thereby spreading the new ASPM variant throughout the population (Frost 2007).


Conclusion

For a brief time, over a decade ago, it seemed we had hard evidence that the human brain was still evolving during the time of recorded history. That evidence was soon rejected and largely forgotten, ironically through the efforts of J. Philippe Rushton. It didn't fit his model. As he saw it, if something fails to correlate with IQ, specifically with the g factor, it cannot be a cognitive ability and is unworthy of interest. 

Rushton was also held back by the idea that human evolution had largely ended with the end of the last ice age. Though intrigued by the contrary idea of ongoing human evolution, he never brought it into his theoretical work and generally treated it like an unwanted strip of film on a cutting-room floor.


References

Abramson, A.S. (2004). The plausibility of phonetic explanations of tonogenesis. In: Fant, G., Fujisaki, H., Cao, J., Xu, Y. (Eds.), From traditional phonology to modern speech processing: Festschrift for Professor Wu Zongji's 95th birthday. Beijing: Foreign Language Teaching and Research Press, 17-29.
http://www.haskins.yale.edu/Reprints/HL1336.pdf

Ali, F. and R. Meier. (2008). Positive selection in ASPM is correlated with cerebral cortex evolution across primates but not with whole brain size. Molecular Biology and Evolution 25(11): 2247-2250.
http://www.haskins.yale.edu/Reprints/HL1336.pdf

Arffa, S. (2007). The relationship of intelligence to executive function and non-executive function measures in a sample of average, above average, and gifted youth. Archives of Clinical Neuropsychology 22(8): 969-978
https://academic.oup.com/acn/article/22/8/969/3025 

Dediu, D., and 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(26):10944-10949
https://langev.com/pdf/dediu07linguisticTonePNAS.pdf

Frost, P. (2007). 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. (2008). Decoding the ASPM puzzle. Evo and Proud, August 27
http://evoandproud.blogspot.com/2008/08/decoding-aspm-puzzle.html  

Mekel-Bobrov, N., S.L. Gilbert, P.D. Evans, E.J. Vallender, J.R. Anderson, R.R. Hudson, S.A. Tishkoff and B.T. Lahn. (2005). Ongoing adaptive evolution of ASPM, a brain size determinant in Homo sapiens. Science 309: 1720-1722
https://www.researchgate.net/publication/7611130_Ongoing_Adaptive_Evolution_of_ASPM_a_Brain_Size_Determinant_in_Homo_Sapiens  
Mekel-Bobrov, N., D. Posthuma, S.L. Gilbert, P. Lind, M.F. Gosso, et al. (2007). The ongoing adaptive evolution of ASPM and Microcephalin is not explained by increased intelligence. Human Molecular Genetics 16(6): 600-608.
https://academic.oup.com/hmg/article/16/6/600/610971

Rushton, J.P., P.A. Vernon, and T.A. Bons. (2007). No evidence that polymorphisms of brain regulator genes Microcephalin and ASPM are associated with general mental ability, head circumference or altruism. Biology Letters-UK 3(2):157-60.
https://royalsocietypublishing.org/doi/full/10.1098/rsbl.2006.0586 

Singh, S.V., N. Staes, E.E. Guevara, S.J. Schapiro, J.J. Ely, et al. (2019). Evolution of ASPM coding variation in apes and associations with brain structure in chimpanzees. Genes, Brain and Behavior 18:e12582.
https://dukespace.lib.duke.edu/dspace/bitstream/handle/10161/19252/Singh_etal2019.pdf?sequence=2

Zhang, J. (2003). Evolution of the Human ASPM Gene, a Major Determinant of Brain Size. Genetics 165(4): 2063-2070.
https://www.genetics.org/content/165/4/2063.short

Zhu, Q., Y. Song, S. Hu, X. Li, M. Tian, Z. Zhen, Q. Dong, N. Kanwisher, and J. Liu. (2010). Heritability of the specific cognitive ability of face perception. Current Biology 20(2): 137-142.
https://www.sciencedirect.com/science/article/pii/S096098220902123X 

The paradox of the Visual Word Form Area

 

Luke the Evangelist (source: British Library). In the past, only a minority could read long texts of cursive writing. But many more could read short texts of block writing.

 

The Visual Word Form Area (VWFA) is a specialized part of the brain that helps us recognize written words and letters. If it is subjected to a surgical lesion, the patient will suffer a clear impairment to reading ability but not to recognition of objects, names, or faces or to general language abilities. There will be some improvement over the next six months, but reading will still take twice as long as it had before surgery (Gaillard et al, 2006).

Most of the initial skepticism over the existence of the VWFA has disappeared. There does seem to be, however, much variability in its size. An area that may fall within this mental organ in one person may fall outside it in someone else (Glezer and Riesenhuber, 2013).

In addition to word recognition, the VWFA may participate in higher-level processing of word meaning:

[It seems that] the VWFA would not only be recruited at an early stage for allowing low-level (script processing) word processing as has been previously instantiated (Pammer et al., 2004; Dehaene and Cohen, 2011), but also at a later stage for gating high-level (lexico-semantic) processing. Such late semantic gateway would not be selective to the VWFA but rather emerge in the posterior LOT and extend anteriorly to the VWFA. (Levy et al., 2013)

The VWFA is described in the above study as a “bottleneck to consciousness.” It helps us not only to recognize words on a page but also to understand what the words mean. To me, this makes sense. I’m better at thinking through an idea and its implications if I can write it down and then read it. There thus seems to be a single mental pathway that does double duty: processing character strings (words) and processing higher-level concepts.

 

Population differences 

The VWFA functions differently in different human populations. The difference is striking between people who use alphabetical script, where each symbol represents a sound, and those who use logographic script, where each symbol represents an idea. Chinese subjects 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).

Hardwired or softwired?

For Dehaene and Cohen (2011), the VWFA is not a hardwired mental organ. They argue that it occupies 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? When kindergarten children were asked to play a grapheme/phoneme correspondence game, their VWFAs preferentially responded to pictures of letter strings after a total of 3.6 hours over an 8-week period. It is worth noting that only a few of these children could actually read, and even then only at a rudimentary level (Brem et al., 2010; Dehaene et al., 2010).

But the alternative view, hardwiring, is also hard to accept. Reading began not in the Paleolithic but in historic times, less than 6,000 years ago. Widespread literacy is even more recent, and there are still many societies where most people cannot read or write. How could an entirely new mental organ have evolved over so short a time?

Yet this alternative view may not be so farfetched. Let’s examine the two main objections.

Was there not enough time for natural selection to work?

The VWFA did not evolve out of nothing. It seems to be a population of neurons that originally served to recognize faces (Dehaene and Cohen, 2011). This sort of recycling is a common pathway for natural selection and explains much of the apparent rapidity of evolution. A complex mental adaptation may take a long time to evolve, but much less time is needed to develop an exaggerated version of it or to alter when and how it becomes activated (Harpending and Cochran, 2002).

Indeed, parallel to the way alphabetical reading ability has spread historically and geographically, there is a similar spread of the latest variant of ASPM, a gene implicated in the regulation of brain growth. In humans, a new variant arose about 6,000 years ago in the Middle East. It eventually became 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). 

Would it have benefited too few people to have been favored by natural selection?

There is some debate over the relative recentness of literacy. It is true that before the modern era only a small minority could read long texts of cursive writing. But the ability to read short texts of block writing was much more widespread, as evidenced by the prevalence of graffiti and storefront signs. We should also keep in mind that the literate few contributed disproportionately to the gene pool of subsequent generations. Clark (2007) has shown that the English lower class is largely descended from people who were middle or upper class a few centuries ago. In the ancient world, there was a perception that scribes enjoyed reproductive success. The Book of Sirach [39: 11] states: “If [a scribe] lives long, he will leave a name greater than a thousand.” 

Gene-culture co-evolution?

There may have been positive feedback between reading ability and the cultural opportunities it created. One example is the scientific revolution in Western Europe (15th - 18th centuries), which took off once a critical mass of scholars could read each other’s papers. In short, reading and writing are advantageous to the extent that other people can read and write. While this kind of feedback loop is self-evident, its biological implications may be less so. The same feedback loop would have steadily ratcheted up selection for the VWFA and, subsequently, for higher-level faculties. This might explain why the VWFA evolved beyond word recognition per se and towards lexico-semantic tasks.

Future research

One priority would be to study the VWFA in populations that have become literate only in recent times. What form, if any, does it take in such people? A study in New York elementary schools found that VWFA activation varied with socioeconomic status. In students from high SES families, activation seemed to be more hardwired and less dependent on familiarity with the way sounds are visually represented. Unfortunately, there was no attempt to break the data down by ethnic background (Noble et al., 2006).

At present, high VWFA activation is attributed to an environment where reading material is accessible and parents very supportive, this being in turn attributed to high SES. Yet reading material is ubiquitous nowadays. And how crucial is parental support? As a child, I read almost always on my own with little encouragement at home or school. My teachers were in fact annoyed by my habit of sneaking into the small storage room where old textbooks and encyclopedias were kept (we had no library). “If you’ve finished your assignment, stay at your desk. Is that clear?!”

Nonetheless, I read voraciously, even when I couldn’t understand half of what I read. Strange new words were a source of pleasure, and I would often read and reread the same texts simply because I liked the flow of the words and the images they conjured up.

 

References 

Brem, S., S. Bach, K. Kucian, T.K. Guttorm, E. Martin, H. Lyytinen, D. Brandeis, and 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.

http://psyserv06.psy.sbg.ac.at:5916/fetch/PDF/20395549.pdf

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

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

http://www.cnbc.pitt.edu/~plaut/VisCog/papers/DehaeneCohen11TICS.VWFA.pdf  

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

http://gondabrain.ls.biu.ac.il/Neuroling/courses/877/Dehaene_Science2010.pdf

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, 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  

Harpending, H., and G. Cochran. (2002). In our genes, Proceedings of the National Academy of Sciences USA, 99(1), 10-12.

http://www.wcas.northwestern.edu/nescan/2008-2009%20papers/harpending%20-%20in%20our%20genes.pdf  

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://psychbrain.bnu.edu.cn/teachcms/res_base/teachcms/upload/channel/file/2010_4/11_25/6hlcggx7rk3z.pdf  
Mekel-Bobrov, N., S.L. Gilbert, P.D. Evans, E.J. Vallender, J.R. Anderson, R.R. Hudson, S.A. Tishkoff, and B.T. Lahn. (2005). Ongoing adaptive evolution of ASPM, a brain size determinant in Homo sapiens, Science, 309, 1720-1722.
http://ftp.eebweb.arizona.edu/faculty/nachman/Archived%20Research%20Papers/mekel_bobrov_et_al_2005.pdf  

Noble, K.G., M.E. Wolmetz, L.G. Ochs, M.J. Farah, and B.D. McCandliss. (2006). Brain–behavior relationships in reading acquisition are modulated by socioeconomic factors, Developmental Science, 9, 642–654.

http://www.cumc.columbia.edu/dept/sergievsky/fs/publications/Noble-et-al-2006-2.pdf  

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.

http://www.drru-research.org/data/resources/42/Paulesu-et-al-2001.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.