HBD: Human Biodiversity

Intelligence, Lifespan, and Race

The differences in average IQ among races has been fairly well-established, with Asians having the highest IQ scores, whites next, and blacks third. This order – Asians, whites, blacks – or the reverse order, can be seen in many aspects of life and society. For instance, crime rates show the reverse order (with blacks having the highest, Asians the lowest); in personality, blacks are more aggressive and more extroverted than Asians, with whites again in the middle. (These examples are all taken from Philippe Rushton's Race, Evolution, and Behavior, where many more examples can be found.) A perhaps less remarked-upon race difference is that of aging and longevity, where again we find the same order: Asians live longest, blacks the shortest, with whites in between. (Asian American women have the highest life expectancy of any group in this country, at 85.8 years.) Naturally, it might be expected that the various factors and outcomes which show racial variation and in the order described here will be correlated, and that is indeed the case. For instance, IQ has been shown to be correlated with longevity.

Why in fact does IQ affect longevity, or maybe vice versa? This is the subject of some debate among IQ researchers. It appears, for example, that those with higher IQ have better health practices (diet, exercise, etc.); they also are more likely to be better informed about health and illness and as such will seek a doctor's care earlier than others, as well as being better able to understand a doctor's orders and comply with them better. (Don't laugh: “26% of the outpatients at two urban hospitals were unable to determine from an appointment slip when their next appointment was scheduled, and 42% did not understand directions for taking medicine on an empty stomach.” [see PDF])

Some researchers have posited the notion that the correlation between longevity and intelligence is due to a so-called “fitness factor”, which makes intuitive sense. Since the brain is the organ of intelligence, and a healthy brain will ceteris paribus be correlated with higher intelligence, and since a healthy brain is more likely to be found in a healthy body, it follows that higher IQ should be associated with health. Indeed, intelligence and semen quality are positively correlated.

A paper by Deary and Der reports that reaction time explains IQ's association with death.

ABSTRACT—Lower IQ is associated with earlier death, but the cause of the relationship is unknown. In the present study, psychometric intelligence and reaction times were both significantly related to all-cause mortality in a representative sample of 898 people aged 56 years who were followed up with respect to survival until age 70. The association between IQ and mortality remained significant after adjusting for education, occupational social class, and smoking, all of which have been hypothesized as confounding variables. The effect of IQ on mortality was not significant after adjusting for reaction time, suggesting that reduced efficiency of information processing might link lower mental ability and earlier death. This new field of cognitive epidemiology provides arguably the strongest evidence for the importance of psychological factors in physical health and human survival. Finding the mechanisms that relate psychometric intelligence to mortality might help in formulating effective interventions to reduce inequalities in health.

Deary and Der hypothesize two possible factors: one, that reaction time picks up subtle clinical factors that affect longevity, i.e. a deteriorating brain is a sign of a deteriorating body; two, the fitness factor noted above, i.e. a fit brain in a fit body.

However, I believe that a case could be made for another factor, one that has to do with the nature of aging itself. Without going into great detail, suffice it to say that the causes of aging are controversial, the most common theory being that aging amounts to the accumulation of damage. The many problems with this theory have led some to an alternate theory, namely that aging is a quasi-program, one that is necessarily the flip side of growth. The same program that causes growth and development causes aging.

This leads us back to racial differences in life expectancy. Since different races grow and mature at different rates, it might be expected that they age at different rates. Blacks mature faster, Asians slower, and Asians live longer, blacks live shorter.

So, while many factors could conceivably link intelligence with longevity, it appears that the very nature of growth and maturation, leading inevitably to aging and death, could be one of them. It's a biological version of “live fast, die young”, and appears to apply to groups of people just as it does to individuals.