The newspaper article summarising the research: http://www.guardian.co.uk/science/2010/jun/30/disease-rife-countries-low-iqs
People who live in countries where disease is rife may have lower IQs because they have to divert energy away from brain development to fight infections, scientists in the US claim.
The controversial idea might help explain why national IQ scores differ around the world, and are lower in some warmer countries where debilitating parasites such as malaria are widespread, they say.
Researchers behind the theory claim the impact of disease on IQ scores has been under-appreciated, and believe it ranks alongside education and wealth as a major factor that influences cognitive ability.
[…]
The actual research article: http://rspb.royalsocietypublishing.org/content/early/2010/06/29/rspb.2010.0973.full?sid=f65fe5b5-b8d4-4e62-82ee-60c7bd44e3d3
Abstract
In this study, we hypothesize that the worldwide distribution of cognitive ability is determined in part by variation in the intensity of infectious diseases. From an energetics standpoint, a developing human will have difficulty building a brain and fighting off infectious diseases at the same time, as both are very metabolically costly tasks. Using three measures of average national intelligence quotient (IQ), we found that the zero-order correlation between average IQ and parasite stress ranges from r = ?0.76 to r = ?0.82 (p < 0.0001). These correlations are robust worldwide, as well as within five of six world regions. Infectious disease remains the most powerful predictor of average national IQ when temperature, distance from Africa, gross domestic product per capita and several measures of education are controlled for. These findings suggest that the Flynn effect may be caused in part by the decrease in the intensity of infectious diseases as nations develop.
For reference, the Flynn effect: http://en.wikipedia.org/wiki/Flynn_effect
The Flynn effect describes an increase in the average intelligence quotient (IQ) test scores over generations (IQ gains over time). Similar improvements have been reported for other cognitions such as semantic and episodic memory.[1] The effect has been observed in most parts of the world at different rates.
The Flynn effect is named for James R. Flynn, who did much to document it and promote awareness of its implications. The term itself was coined by the authors of The Bell Curve.[2]
The effect’s increase has been continuous and approximately linear from the earliest years of testing to the present. There are numerous explanations to the Flynn effect and also some criticism. There is currently a discussion if the Flynn effect has ended in some developed nations since the mid 1990s.