Disease and intelligence

Parasites and pathogens may explain why people in some parts of the world are cleverer than those in others

HUMAN intelligence is puzzling. It is higher, on average, in some places than in others. And it seems to have been rising in recent decades. Why these two things should be true is controversial. This week, though, a group of researchers at the University of New Mexico propose the same explanation for both: the effect of infectious disease. If they are right, it suggests that the control of such diseases is crucial to a country’s development in a way that had not been appreciated before. Places that harbour a lot of parasites and pathogens not only suffer the debilitating effects of disease on their workforces, but also have their human capital eroded, child by child, from birth.

Christopher Eppig and his colleagues make their suggestion in the Proceedings of the Royal Society. They note that the brains of newly born children require 87% of those children’s metabolic energy. In five-year-olds the figure is still 44% and even in adults the brain—a mere 2% of the body’s weight—consumes about a quarter of the body’s energy. Any competition for this energy is likely to damage the brain’s development, and parasites and pathogens compete for it in several ways. Some feed on the host’s tissue directly, or hijack its molecular machinery to reproduce. Some, particularly those that live in the gut, stop their host absorbing food. And all provoke the host’s immune system into activity, which diverts resources from other things.

The other prediction, of course, is that as countries conquer disease, the intelligence of their citizens will rise. A rise in intelligence over the decades has already been noticed in rich countries. It is called the Flynn effect after James Flynn, who discovered it. Its cause, however, has been mysterious—until now. If Mr Eppig is right, the near-abolition of serious infections in these countries, by vaccination, clean water and proper sewerage, may explain much if not all of the Flynn effect.

When Dr Lynn and Dr Vanhanen originally published their IQ data, they used them to advance the theory that national differences in intelligence were the main reason for different levels of economic development. This study turns that reasoning on its head. It is lack of development, and the many health problems this brings, which explains the difference in levels of intelligence. No doubt, in a vicious circle, those differences help keep poor countries poor. But the new theory offers a way to break the circle. If further work by researchers supports the ideas of Mr Eppig and his colleagues, they will have done the world a good turn by providing policymakers with yet another reason why the elimination of disease should be one of the main aims of development, rather than a desirable afterthought.


http://www.economist.com/node/16479286?story_id=16479286&fsrc=scn/tw/te/rss/pe

Healthcare for None by the year 2010.
An addition to the numerous ways our leaders continue to under-develope our country.