The Genetic Origins of The Nerd Stereotype

“Stereotypical nerd appearance, often lampooned in caricatures, can include very large glasses, braces, buck teeth, severe acne and pants worn high at the waist.” 

Why is there a physical stereotype associated with being a nerd, something that is typically defined by mental characteristics (most notably high intelligence)? Is there some deeper connection here between intelligence, poor eyesight, and acne?

Eyesight and Intelligence

The correlation between poor eyesight (more specifically myopia or short-sightedness) and intelligence (as measured by IQ) seems to be particularly robust and well-studied so let’s start there. We can imagine a few explanations for why this relationship might exist. The common-sense explanation would be that intelligent people are more likely to enjoy reading (or other traditionally nerdy activities that require one to focus on something close up), and thus are more likely to develop myopia. Another possibility is that poor eyesight by itself has some kind of enhancing effect on intelligence.

Alex Guzey discusses the logic behind this explanation:

“We know that losing one sense makes you better at others [1, 2, 3, 4]. For example, losing eyesight improves hearing. Why? Apparently, (in the event of blindness) the brain rewires itself and uses the visual areas as auditory ones [3]:

Vision is such an important sense for humans that a huge portion of the brain is devoted to visual processing—far more gray matter than is dedicated to any other sense. In blind people all this brain power would go to waste, but somehow an unsighted person’s brain rewires itself to connect auditory regions of the brain to the visual cortex.

Well, why make this a dichotomy? It seems natural, that losing some eyesight during the critical period (i.e. childhood myopia), if left uncorrected, would cause some of the changes that we encounter in fully blind people. We already observe how the brain changes itself during the process of learning to read [5, 6, 7, 8, 9]!

Why do we lose vision in the first place? Many hypotheses, but one I like the most: being inside. So, a child likes reading –> spends time inside, instead of playing outside –> eyesight deteriorates –> parts of the visual cortex rewire themselves to other areas

What are books (especially fictional)? They’re essentially a tool that translates persistent visual deprivation into narrative-driven visual hallucinations. So we would expect that the visual neurons get recruited in the parts of the brain responding to “imagination”.

Interesting. There are a few ideas here, but the important one for our purposes is that a loss of vision in childhood can free up neural resources that can then be put towards enhancing something else like general intelligence or imagination (we might call this the compensation effect for lack of a better name). The compensation effect provides a theoretical reason for why poor eyesight on its own, and not reading, might cause increased intelligence.

So we have two models – (1) intelligent people are more likely to acquire poor vision from reading too much and (2) poor eyesight (either caused by genetics or environment) allows for a compensating mechanism that enhances intelligence. What does the research say about the relative importance and plausibility of these models?

A study entitled “Phenotypic and Genotypic Correlation Between Myopia and Intelligence” seems to be the most recent and comprehensive look at the question.

“Of the small phenotypic correlation the majority (78%) was explained by genetic factors. Polygenic risk scores were constructed based on common genetic variants identified in previous genome-wide association studies of refractive error (a measure of myopia) and intelligence. Genetic variants for intelligence and refractive error explain some of the reciprocal variance, suggesting genetic pleiotropy; in the best-fit model the polygenic score for intelligence explained 0.99% (p=0.008) of refractive error variance. These novel findings indicate shared genetic factors contribute significantly to the covariance between myopia and intelligence.”

This result, if I understand it correctly, means that about 78% of the correlation between intelligence and myopia is explained by genetics and that the genetic variation in intelligence (the polygenic score) explains about 1% of the variation in myopia. This may seem counterintuitive, but although intelligence and myopia have just a small fraction of shared genetic factors, these factors are responsible for most of the observed correlation between these traits at the population level.

This surprised me - the conclusion is that most of the connection between myopia and intelligence is explained by genes and not environment (i.e. reading) (edit - but maybe I shouldn’t have been surprised, see Emil O. W. Kirkegaard’s comment below). The commonsense story of smart nerds having glasses because they read a lot does not seem to be supported. The authors elaborate on this result at length in the discussion:

“The argument that highly intelligent children, who may spend more time on near-work activities, increase their risk of developing myopia has long been favored. However the association between near-work and myopia is inconsistent, and importantly refraction in young children, prior to the experience of intensive education and near-work, can significantly predict those who will later become myopic. The possibility that increased time studying can increase an individual’s IQ has been largely discounted; there is no robust evidence that a large effect on IQ can be achieved by such an intervention. Shared genetic factors may play a role in both traits. Early proponents for this theory identified an association between myopia and IQ where the intellectual gain preceded the development of myopia, and differential status in siblings. A single myopia gene that influenced brain development with evolutionary advantages for urbanized living was proposed. The idea of a single gene controlling brain development and eye growth, in light of modern knowledge of the polygenicity of both traits, now appears implausible. However, the possibility of a number of genes of small effect, perhaps inherited simultaneously and linked, that control neural signaling influencing ocular growth and learning abilities remains interesting.”

It seems these authors favor a different mechanism than the compensation model for how myopia and intelligence may be biologically linked. In the compensation model, a gene that causes worse eyesight has the indirect effect of enhancing intelligence through compensatory neuroplasticity. The authors of this article suggest a model in which the activity of a gene has a direct effect on both traits (i.e. the genes are pleiotropic).

“In axial myopia, the commonest form of myopia, elongation of the eye results in a focused image falling in front of the retinal plane. The retina, together with a number of other ocular structures, including the ciliary body which controls accommodation (near focus), originate embryonically from the same tissue as the brain (neuroectoderm). Retinal signaling, through detection of focused light, influences scleral remodeling and ultimately ocular axial length. Therefore, could the same genetic factors in the retina and brain theoretically be involved in the regulation of both structures? There is some evidence that people with high IQ have a ‘larger brain’, with correlations estimated at 0.38 to 0.45. Brain size itself does not predict cognitive ability within families, although incorporating other neuroimaging variables can provide a modest prediction of IQ variance.”

So maybe a gene that causes you to grow longer axons could cause bad vision and a bigger brain?

Acne and Intelligence

So what about acne? We can basically map the same explanations from myopia on to the link between acne and intelligence.

Behind door 1, we have the more common-sense explanation that it’s the acne itself that leads to increased intelligence. Acne makes one shy and less confident (I know it did in my case), which leads to less social interaction and increased participation in more solitary pursuits that tend to be more intellectual (like reading), thereby enhancing intelligence. We can concoct a compensation effect story like we did for eyesight – nerdy children spend less time interacting socially so their brains spend less neural resources on developing social cognition, and thus can spend more resources on things like mathematical intelligence. Acne seems to be predominantly caused by genetics (roughly 80% heritable) so this explanation means that genetics are still largely responsible for the link between acne and genetics. Behind door 2, we have the purely genetic explanation – acne and intelligence have shared genetic factors (either by pleiotropy or genetic linkage); this is the same model discussed above for eyesight and intelligence.

If we take anything from the story on myopia and intelligence, we might suspect that the more common-sense explanation (door 1) is incorrect. What does the research say about the purely genetic explanation (door 2)? A quick investigation shows we might have put the cart before the horse – are we even sure that intelligence and acne are correlated? The closest thing I can find is a study that shows a relationship between educational attainment and acne.

“The love of books, the need for glasses and high intelligence are traits found among the top earners in many fields across the country. Now, a Ball State University researcher suggests that a case of acne in high school should be added to those traits.

In his study, "Do Pimples Pay? Acne, Human Capital, and the Labor Market Abstract," Erik Nesson, a Ball State economics professor, found that having acne is positively associated with overall grade point average in high school, grades in high-school English, history, math, and science and the completion of a college degree.”

This study only demonstrates an association between educational attainment and acne – this could easily be explained by motivation or social environment and not necessarily higher intelligence (i.e. people with acne are more motivated to do well in school and have more time to do so because they don’t have as many friends).”

So it is possible that acne isn’t necessarily associated with intelligence. The fact that acne is associated with educational achievement is certainly suggestive though (because educational attainment and IQ are highly correlated), and I can’t find any evidence showing that there is not a connection between them.

I can find exactly one article that hints at a biological connection between acne and intelligence, but it has a very different focus and doesn’t really answer why these two traits might be correlated within human populations. Interestingly, acne seems to be almost solely a human phenomenon, the only other examples being the very minor forms found in cats and dogs (perhaps it’s notable that the only examples of animal acne are from domesticated animals that live the same environments as us). Why might this be? The proposed hypothesis is fascinating and kind of hilarious.

“Acne is a disease unique to humans and is associated with sebaceous glands that are found in a high density on the scalp, forehead and face. Despite being a near universal problem in adolescence, the reason why such troublesome sebaceous glands exist at all is not well understood. Some interesting theories have been postulated including roles for skin maintenance, immunological function and perhaps even pheromones, but pre-pubertal skin which has sebaceous glands that are largely inactive, is healthy. Dystocia, obstructed labour, is unique to humans and no other animal has as much trouble giving birth as humans. This is thought to reflect the relatively large human foetal head and proportionally small maternal pelvis. There is high density of sebaceous glands on the face, chest and back; these are exactly the same structures that pose the greatest obstruction during childbirth. Sebaceous glands develop after the fourth month of gestation and are large and well-developed at birth. Sebum production is also relatively high at birth. Having extra lubrication at these sites would help make the baby more slippery for birth conferring a selective advantage to successful delivery, as does the presence of the vernix caseosa, a white creamy substance, unique to humans that coats newborn infants. It is proposed that the sebaceous glands that cause acne are present on the face and forehead as they confer a selective advantage by ‘lubricating’ the widest parts of the newborn baby to ease the passage of childbirth. Later in 3 life, sebaceous glands may be inappropriately and pathologically primed, driven by a combination of hormones, diet and lifestyle to create acne.”

So the reason humans have acne might be because we needed to lubricate our big heads so they could slide out of the vagina during childbirth? This sounds just ridiculous enough to be true. Jokes aside, this does suggest one interesting hypothesis – the correlation between acne and intelligence arises from the correlation between head size and intelligence (head size and intelligence are correlated in adults, and head size at birth does show a correlation with IQ later in life). Thus, the selective pressure favoring a genetic and phenotypic linkage between acne and intelligence comes from the fact that big-headed babies need more lubrication. A first step towards finding evidence for this model would be to look at the relationship between acne and head size, something that has never been studied as far as I can tell from a quick search.