Malaria and IQ

The figure below, from Bill Gates's annual letter, shows that countries with a higher disease burden have lower average IQs. The theory is that building brains and fighting disease are metabolically costly so more effort to fend disease diverts resources from brain development lowering IQ. 

Tyler blogged this research earlier writing "I'm not sure the authors have a very good test against alternative hypotheses, but still a correlation remains after making some appropriate adjustments."

Further evidence on causality is given by Atheendar Venkataramani in Early Life Exposure to Malaria and Cognition and Skills in Adulthood. Venkataramani finds that men born after widespread malaria eradication began in Mexico in the late 1950s have higher IQs (Raven scores) and are more likely to work in white collar jobs than men born shortly before eradication efforts began. Importantly, the effect is larger for men born in those states that began with high exposure to malaria.   


I am glad I am so healthy, so that I could become super-smart. Unfortunately, I had no energy left to build up any sense of modesty.

That's what Bill Gates said. :O

I'd be inclined to trust the individual-level data much more than the country level stuff. I haven't actually bothered to check the paper, so I could be completely off base with this, but last I looked into it, most of the country-level IQ data available was pretty rubbish. (Very little based on actual tests, lots of data points imputed, which leads to confounding, etc.)

Who believes in IQ tests in this day and age anyway????? Just because it is something that people measure, has numbers attached to it and can be plotted on a chart do not mean it has meaning. Not to mention all the other caveats.

Shouldn't the measure be IQ of infected individuals vs that of the disease free living in the same country? Otherwise how do you filter out IQ variations resulting from nutrition, cultural factors, etc. ?

After thinking about it some more, I'm willing to bet the countries at both extreme levels are simply smaller countries where variance of the population around the mean is higher. If there's a relationship between size and geographic location of countries, that should be controlled. It may just be the case that you have a lot of small African and Latin American countries with high IQ variance due to small size and high rates of malaria due to location, and there could be other well-known factors that impact the IQ level directionally. Didn't Bill Gates' foundation make a similar mistake when they showed that the best performing schools tended to be smaller ones?

Lou, Huh? You think small countries have low average IQ because of random variance? How big do you think these countries are, population of 10? If that is what you mean, that is clearly wrong. Even for 100 people it would be extraordinary to get a 70 average if the expected average is 100 or even 85.

Cliff, I said I'm "shocked" and I "have a hard time believing" (my exact words) that there would be countries with an average IQ below 70.

@ Lou - there may be different IQ scales used so what does 70 mean? On some scales a little below that of the chimpanzees who used to drink tea for the famous Brooke Bond advert - on others above the level needed for literacy.
I personally find it difficult to believe that there are any countries with an average IQ below 70 on almost any scale that does not produce results below zero for individuals - it is possible for the average IQ test scores to be below 70 if that country has a high level of illiteracy so that a lot of test papers score zero if the testee cannot read the question, or if the IQ test is prepared by an American who imagines everyone in the world shares his/her cultural background and worldview.
MENSA used to set its scale at 147.6 was the level above which you had 2% of the world population but some modern scales have 0.01% above 148, so on the MENSA scale 70 would be the benchmark for the bottom 10% of the population and in the latter case for the bottom 2.7% of the population, but an arithmetical average would mean a single guy with my father's IQ (or my son's or any guy in my family except me) would need to be offset by a guy or two with *negative* IQs.

actually , i would think GDP vs IQ would also have a higher correlation

I suppose "Smart People Move Away" would be have been far too succinct and pithy for something as important as the Bill Gates Annual Letter.

Malaria and other diseases impose a huge burden on the body. Instead of using energy to build better bodies and minds, energy is used instead to simply survive the effects. It also consumes resources that are used to compensate for the effects of the disease (such as lower productivity) that could be used on things that would benefit IQ or development in general (such as schooling).

There is also the problem of lead exposure in many poor countries. I believe lead has clear effects on IQ and in many poor areas large groups are exposed to lead in water, paint, etc. So malaria+lead+random diseases+poverty and poor nutrition could easily damage IQ. Remember a third of the world lives on well under $2 per day and doesn't have clean water.

You can see how severe a fitness burden falciparum malaria is in what evolution has whipped up to fight: the sickle cell mutation. If you inherit one copy of the sickle cell allele, you are more likely to survive malaria, although your overall energy level will likely be somewhat lower. If you inherit two copies, you die (without modern medical care). That's pretty harsh.

Garbage in... Bill Gates out...

John77, in what way does it not fit with "elementary mathematics"? The only IQ scale I have ever heard of being used is Stanford-Binet. A person can have an IQ below 20 but cannot have a negative IQ.

The general rule is that, as Kingsley Amis said in Lucky Jim: "There was no end to the ways in which nice things are nicer than nasty ones."

The paper by Eppig et al that Bill Gates cites includes a potential evolutionary explanation for why selection might favor immune system over intelligence in high disease burden regions:

"We also propose a complementary hypothesis that may explain some of the effects of infectious disease on intelligence. As we mentioned, it is possible that a conditional developmental pathway exists that invests more energy into the immune system at the expense of brain development. In an environment where there has consistently been a high metabolic cost associated with parasitic infection, selection would not favour the maintenance of a phenotypically plastic trait. That is, the conditional strategy of allocating more energy into brain development during periods of health would be lost, evolutionarily, if periods of health were rare. Peoples living in areas of consistently high prevalence of infectious disease over evolutionary time thus may possess adaptations that favour high obligatory investment in immune function at the expense of other metabolically expensive traits such as intelligence."

Jeffrey Sachs created an index of the disease environment of a location based on purely geographic and climate-related factors -- that is, it should be exogenous to things like sanitation and public health programs. If we had better IQ data, one could correlate this index to IQ test scores. Unfortunately, IQ data for most poor countries -- to say nothing of localities in those countries -- is crap.

Your question is like asking "How can a country have an average income of $1/day when it is possible for a person to have an income of $1 million/day". It makes zero sense.

As already mentioned, what is the quality of the data? The fact that so many countries seem to have an average IQ below 70 does not make sense. According to the (APA) DSM-IV-TR an IQ between 55-70 implies that you have "mild mental retardation".

If you argue that these data are reasonable, do you argue that the average person in up to a 1/4 of the countries have mild mental retardation? Interesting...

IQ statistics are the product of education. Well educated societies have high IQ. Well educated societies are developed societies. Developed societies are less prone do disease. South Korea has the highest IQ in the world because South Koreans study 12 hours a day. High national IQ is the product of hard work, not innate intelligence.

IQ and disease are negatively correlated for the same reason that porn sales and disease are negatively correlated: wealthy societies are better educated and consume more porn.

About the thesis that African countries have low IQ because their population has developed less brains and more immune system well that's plain racist crap. The same type of crap eugenicists did 100 years ago.

Obviously there may be more to it than what Bill Gates shares from his research. Read Freakonomics. At the same time, it makes sense that the healthier the bodies of the parents, the mother during pregnancy and the offspring through life, the better chances they have for a brighter mind.

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