Why is vocabulary shrinking?

Vocabulary decline in adult non-Hispanic White Americans (controlled for years of education completed)



"Are Americans more intelligent than a few decades ago, or less intelligent?" So asks psychologist Jean Twenge in her introduction to a recent paper on vocabulary decline in Americans. The findings are disconcerting, to say the least:

We examined trends over time in vocabulary, a key component of verbal intelligence, in the nationally representative General Social Survey of U.S. adults (n=29,912). Participants answered multiple-choice questions about the definitions of 10 specific words. When controlled for educational attainment, the vocabulary of the average U.S. adult declined between the mid-1970s and the 2010s. Vocabulary declined across all levels of educational attainment (less than high school, high school or 2-year college graduate, bachelor's or graduate degree), with the largest declines among those with a bachelor's or graduate degree. (Twenge et al. 2019)

The last decline was especially large: more than half a standard deviation. In general, vocabulary test scores have fallen by 8.5%. Ethnic change doesn’t seem responsible, since non-Hispanic whites have had almost the same decline: 7.2%.

So what's going on? The authors considered the explanation they first raised: Americans have become less intelligent despite the increase in education.

First, Americans' vocabularies might be shrinking despite the increase in education. This is plausible given the steep decline in the amount of time high school students spend reading [...] and the decline in SAT verbal scores over time [...]. This explanation could account for the narrowing of abilities between those without high school educations and those with college educations. The difference in vocabulary by education was approximately 3.4 correct answers in 1974-79 but dropped to 2.9 correct answers by 2010-16. However, this explanation would not account for the decline in performance in all educational groups. (Twenge et al. 2019)

Uh, why not? The last sentence makes sense if the explanation is simply that postsecondary education has become less effective. But what if vocabulary has declined because the capacity for learning words and retaining them has also declined? The cause may be genetic. Can we at least ask that question?


Lower admission standards? Mismatch between cause and effect

The authors then consider another explanation: because college admission standards have been lowered, people of lower ability have been going on to postsecondary education in larger numbers; those who don't are increasingly the least able.

If education does not improve vocabulary, but educational attainment increases, those with higher ability will be increasingly selected into the higher education groups, leaving those with lower ability in the lowest educational attainment groups. Thus, the no high school degree group will be left with those of lowest ability, and the college graduate group will have absorbed more with only moderate ability. (Twenge et al. 2019)

That explanation is popular, but it doesn’t really match the findings. The vocabulary decline was steepest during the late 1970s and early 1980s. It then levelled off. A second decline may have begun in 2008, but it’s still too early to say (see Figure 1 reproduced above). Most of the decline doesn't correspond to any previous change in college enrollment by recent high school graduates. The enrollment rate rose slowly from 45.7% in 1959 to 49.4% in 1980. It began to grow faster only in the mid-1980s, breaking through the 60% level in 1991 and the 70% level in 2009 (Bureau of Labor Statistics 2010).

So the alleged cause doesn’t match the presumed effect. The steep increase in college enrollment from the mid-1980s onward could not have caused the steep vocabulary decline during the late 1970s and early 1980s. Keep in mind that most of the GSS respondents had completed their education some years earlier, almost ten years earlier on average. So the average respondent in the late 1970s had to meet college admission standards that existed in the late 1960s.


Most of the decline has been among early boomers

Because the GSS was first administered in 1974, we don't know when the steep vocabulary decline began. But we do know when it ended: in the mid-1980s, among respondents who were born on average thirty years earlier. A genetic cause would imply a rapid deterioration in the gene pool from 1945 to 1955 and a slower deterioration thereafter. I have no idea what that cause could be.

If we're looking for a cultural cause, it would have acted most strongly on the same cohort of "early boomers." Perhaps it was their increasing exposure to TV and their decreasing exposure to high literature. Those cultural changes were already a fait accompli for "late boomers," who experienced a more gradual dumbing down of vocabulary on TV and in print. The post-2008 vocabulary decline, if it’s real, might reflect the growing importance of iPhone texting since the late 2000s.

That cultural explanation has some support from the data and is favorably mentioned by the authors. For one thing, comparison with the results of another test (WAIS) suggests that the decline has been mostly in passive vocabulary, i.e., the words we understand but don’t use spontaneously in speech (Twenge et al. 2019). We’re less proficient in "bookish" language:

Perhaps American culture became less intellectual, either because of or in response to a lowering of verbal ability among those who read books. Authors aim to sell more copies of their books, and thus may adjust their vocabulary level to the skills and preferences of a wider slice of the population. Or, perhaps authors lowered the vocabulary level of their books for some other reason such as an interest in getting out a message without linguistic complexity getting in the way. For example, the Bible has been revised repeatedly to make it more accessible with the King James Version, the most complex and lyrical English language version, being succeeded by the simpler New International Version, Living Bible, and New Revised Standard Version. (Twenge et al. 2019)

The last point rings true. When I was studying Shakespeare in high school my mother could explain words I had trouble understanding. She had never gone beyond Grade 10, but she could read the Bible in the King James Version, as well as a lot of high-brow literature. This was true for many ordinary adults in the 1970s. Today, regular reading of the Bible is unusual and almost always confined to modern English versions.


Conclusion

Yes, college has become a less interesting place for learning vocabulary, and for learning in general. Yes, a big reason is the growing number of students who don’t really belong there, and the consequent lowering of standards. Yes, America’s cultural and linguistic mix is changing, and for that reason alone the average American would have a smaller English vocabulary.

Nonetheless, those factors fail to explain why non-Hispanic white Americans know fewer words today than they did a half-century ago, especially in their passive vocabulary. Something else is going on, and it seems to be a shift away from high literature and toward simpler audiovisual media: TV, video, text messaging …


References

Bureau of Labor Statistics. (2010). College enrollment up among 2009 high school grads. TED: The Economics Daily. April 28
https://www.bls.gov/opub/ted/2010/ted_20100428.htm?view_full

Twenge, J.M., W.K. Campbell, and R.A. Sherman. (2019). Declines in vocabulary among American adults within levels of educational attainment, 1974-2016. Intelligence 76: 101377
https://www.gwern.net/docs/iq/2019-twenge.pdf

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 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.

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.