DRUSE

Ian Deary wrote an essay in Nature (13 November 2008) about intelligence and ageing. At the outset, he stressed the validity of intelligence tests:

“Scores from cognitive-ability tests (also known as intelligence tests or IQ tests) have validity that is almost unequalled in psychology (Deary, 2001).”

He highlighted four non-exclusive possibilities for the link between intelligence and death:

“First, what occurs to many people as an obvious pathway of explanation, is that intelligence is associated with more education, and thereafter with more professional occupations that might place the person in healthier environments.”

“Second, people with higher intelligence might engage in more healthy behaviours.”

“Third, mental test scores from early life might act as a record of insults to the brain that have occurred before that date.”

“Fourth, mental test scores obtained in youth might be an indicator of a well-put-together system.”

He wrote further:

“Although intelligence plays a part in health behaviours and health outcomes that contribute to specific causes of death, a clear chain of causation from intelligence to health outcomes and then to death has not emerged. Different types of mortality, including cardiovascular disease, homicide and suicide, seem to demand their own explanations for being associated with early-life intelligence. Those who found the intelligence–death association ‘obvious’ must think again.”

In the end, he asked:

“Why do we die when we do, and to what extent is this question tractable?”

Deary, I. J. Intelligence: A Very Short Introduction (Oxford Univ. Press, 2001).