Edward M. Miller (2000) Brain and eye Size, Myopia and Intelligence. Psycoloquy: 11(104) Brain Intelligence (4)

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PSYCOLOQUY (ISSN 1055-0143) is sponsored by the American Psychological Association (APA).
Psycoloquy 11(104): Brain and eye Size, Myopia and Intelligence

Book Review of Storfer on Brain-Intelligence.

Edward M. Miller
Professor of Economics and Finance
University of New Orleans
New Orleans, LA 70148
504-280-6913 (work)
504-283-3536 (home)
504-280-6397 (fax)



The major facts Storfer (1999, 2000) attempts to explain by unorthodox theory are easily explained within the framework of traditional genetics and evolutionary theory. The correlation of IQ and myopia may be due to a single gene affecting both brain size and eyeball size, or by high intelligence leading to studying leading to myopia. There are plausible evolutionary theories to explain ethnic group differences in intelligence and myopia.


allergy, brain size, development, evolution, gene expression regulation, genomic imprinting, gifted, intelligence, myopia, neocortex.
1. Storfer (1999, 2000) documents well the correlation between myopia and intelligence, the increasing rate of myopia in recent years, the increase in intelligence over time, the correlation between IQ and brain size (the Flynn/Lynn effect), and the higher IQ and myopia in Jewish and Oriental populations. His documentation here is good and he reaches the same conclusions others and I have reached from the literature. However, he feels it necessary to explain these well-established facts by the inheritance of acquired characteristics, proposing mechanisms by which this could occur. He evidently believes traditional genetic mechanisms cannot explain the facts he has documented.

2. This commentary will point out how these facts can be explained by standard genetic mechanisms. Once this is done there is little need for postulating the inheritance of acquired characteristics. Storfer also seems to feel that traditional genetics cannot reconcile the observed secular growth in IQ and myopia with the evidence that both IQ and myopia are subject to considerable genetic influence. Saying these traits are highly heritable is merely saying that a high percentage of the variability at a particular time is explained by hereditary. This is quite consistent with large changes over time in the same trait being caused by environmental factors. There is a large literature speculating about why intelligence scores have been rising over time. Jensen (1998, 1999), among others, has discussed this literature. Plausible causes include improved nutrition (Lynn, 1990) or health, and greater exposure to sophisticated graphic images from TV and computers. Storfer presents a new theory of myopia being caused in the brain by visual complexity. Given the strong evidence for the standard theories that explain myopia by events occurring within the eye (Curtin 1985), there is little need for a new, brain centered theory.

3. While Storfer finds the Asian increase in myopia hard to explain, it is very plausibly explained by the increased studying being done in these Asian countries. Research shows that near work can increase myopia (Kinge, Midelfart, Jacobsen, & Rystad, 2000; Parssinen, & Lyyra 1993). There is no need to resort to a new biology of inheritance. Although myopia is considered a partially heritable condition, there is no logical problem in a condition whose cross sectional variability indicates a strong genetic component changing over time for environmental reasons. Storfer apparently finds the observed correlation between intelligence and myopia is something that can only be explained by a new theory for the causation of myopia. However, there are at least two ways to explain it within traditional theory.

4. An obvious explanation for the high correlation between intelligence and myopia, both within and between populations is that high intelligence leads to more reading, and this leads to greater myopia. The chief obstacle to accepting this theory is the very convincing evidence that myopia (whose proximate cause is a difference between the focal length of the lens and the length of the eyeball) has a very high heritability (Curtin 1985, Francois 1961). However, there is also evidence that near work can lead to myopia (Young, 1975, Working Group on Myopia Prevalence and Progression, 1988, Kinge, Midelfart, Jacobsen, & Rystad, 2000; Parssinen & Lyyra 1993). Close work cannot be the whole story because refractions at six to twelve months (well before the start of schooling) predict later myopia (Pacella et al. 1999).

5. The heritability data can be reconciled with a large role for environmental conditions (notably the extent of near work), if what is inherited is not merely the dimensions of the eye under normal conditions, but a tendency to seek out certain environments, such as those that involve near work. Both inheritable personality traits (introversion) and inherited high intelligence could lead to more studying and other close work. Indeed, Chen, Cohen, and Diamond (1985), in a study of 361 Taiwanese twins, found that monozygotic twins showed a highly significant tendency (p < .001) to be more concordant in the amount of studying and reading done (72% concordant) than dizygotic twins (52.3%), suggesting substantial behavioral heritability. Considering only twins who were concordant in near work, the monozygotic twins were 83.6% concordant, whereas the dizygotic twins were only 59.5% concordant, showing substantial genetic influence after controlling for behavior (p < .001). Statistically significant effects for the amount of near work were shown by considering only monozygotic twins, who of course have the same genes, and who were found to be 92.2% concordant for myopia when they were also concordant for the amount of near work, versus 79.3% concordant for myopia when they were discordant for the amount of near work.

6. An alternative genetic theory to explain why myopia is much more common among the highly intelligent exists. I (Miller 1992) have argued that there is a pleitropic genetic effect by which one gene promotes growth of both the brain and the eyeball, with the eyeball growth leading to myopia, or a predisposition to myopia. Although eminently testable, there is no report in the literature of it being tested.

7. A quick summary of the evidence for this theory may be useful. Cohn, Cohn, & Jensen (1988) showed that not only was myopia more common among highly intelligent children, but that myopia was more common among them than among their less talented siblings. Benbow (1986, 1988) showed that myopia was more common among her sample of extremely mathematically and/or verbally precocious students (top 1 in 10,000) than among the general population, and that it was more common among these students than among their siblings, again suggesting that some genes affect both intelligence and myopia. Karlsson (1978, chap 9 and 10; 1991, pp. 39-45, 137-143) summarized in non-technical language both the evidence for the inheritance of myopia, and for a correlation of myopia and intelligence. He (1978, p. 76; 1986) hypothesized that both myopia and intelligence might be affected by a single gene, which he estimated (from his data on California children) contributes about eight IQ points to intelligence. The only problem is to plausibly explain why one gene might affect head size and IQ.

8. The proximate cause of myopia is known to be an eyeball that is long relatively to the focal length of the lens (Curtin 1985). Such a physical trait is very plausibly subject to strong genetic influence. It is also known that brain size and IQ are correlated. (I summarized the evidence in my papers and Storfer has summarized it in the target paper). Embryologically, the eye is an outgrowth of the brain. This makes it very plausible that one growth related gene could affect the size of both the eyeball and the brain. While a proportionately larger eye would not be more prone to myopia, the cornea and lens develop from the surface ectoderm of the embryo, whereas the retinal tissues develop from the neural ectoderm (Barber, 1955). Thus, the hypothesized gene for a larger eyeball and brain need not result in a proportionately greater increase in the focal length of the eye. A study of Japanese school children (Otsuka, cited by Baldwin, 1981, p. 520) reported "the result that a person with a better scholastic record has a longer axial length and a smaller refractive power of the lens than a person having a poor scholastic record." The refractive power of the cornea was virtually the same for both groups.The above theory is easily tested. I understand the late Professor Willerman at the University of Texas started a study of the correlation of head size, eye dimensions, and myopia, but I am aware of no publication of his results.

9. If such a polymorphic gene exists, it can easily explain the IQ myopia correlation, without the very speculative mechanism Storfer proposes. Since the IQ myopia correlation might also be explained by the intelligent doing more reading and studying, there really seems no reason to postulate a new inheritance mechanism. Storfer seems unwilling to regard ethnic group differences in intelligence (in Jews and Asians especially) as being due to genetic causes. However he does seem to recognize that such differences exist and that standard environmental mechanisms are inadequate to explain them. While many are unwilling to use traditional genetics to explain differences between ethnic groups in intelligence, traditional genetics can easily handle the problem. With reproductive isolation for many generations and stronger selection for a trait in a population, that trait can be expected to emerge at higher levels.

10. MacDonald (1994) has explained the evolution of higher Jewish intelligence in a way that is consistent with standard genetic theory. Many, including Rushton (2000) and myself (Miller 1995) have provided theories that can explain the higher intelligence of Orientals using standard natural selection theories. I explain the higher Oriental intelligence by differences in the climates in the regions where they evolved, with the Orientals having evolved in somewhat colder climates. In my differential paternal investment theory (Miller 1994), the females evolving in the coldest climates were dependent on males for provisioning. This in turn led to large differences in many traits. Cold climates select for intelligence because males need intelligence to avoid being cuckolded, and females need intelligence to avoid being impregnated by males who will not help raise their offspring (Miller 1994). While it may be politically more correct to explain group differences in intelligence by the inheritance of acquired characteristics, traditional evolutionary theory appears up to the problem.

11. Admittedly, the speculations of Storfer just might prove to be true, although no real case for them has been made so far. Perhaps information relevant to the construction of the brain is transferred other than through the genome. Interestingly, evidence has been presented that most of the mouse brain, including the cortex, is made by maternal genes (Allen et al 1995). If anything, this goes against the disproportionate role for males that Storfer hypothesizes.

12. The major facts Storfer attempts to explain by unorthodox theory of the inheritance of acquired characteristics including the correlation of myopia and intelligence, the increase over time in myopia and intelligence, and ethnic group variations in intelligence and myopia are easily explained within the framework of traditional genetics and evolutionary theory.


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