This stunning chart is in Bill Gates’ annual letter. It shows that people in countries with a heavier burden of infectious disease tend to have a lower I.Q.
Apparently this is due to several factors. Malaria directly damages the brain of those infected. Children with infectious diseases don’t get enough nutrition for their brain to develop properly. But it also has to due with the body’s allocation of resources: where the prevalence of disease s high people must spend energy that would otherwise be used on brain development on fighting it
Thanks to Alex Tabarrok at Marginal Revolution for the pointer.