The parasite-stress hypothesis
I ran across an interesting article in this week's Economist, which covers a new paper in the Proceedings of the Royal Society of Biology--an ecologic study that correlates countries' population burden of infectious diseases to levels of intelligence. The authors of the paper conclude that countries with the the highest rates of infectious diseases have the lowest IQs, even when controlling for confounders such as GDP, education, and climate. The investigators hypothesize that the energy consumed by infections in early childhood affect brain development, leading to lower intelligence. The paper is intriguing, the association seems biologically plausible, and the authors seem careful to identify potential confounders and caution the reader on the limits of observational studies.