Cognitive Daily

Low IQ leads to a short life?

The BPS Research Digest is reporting on a new article by Satoshi Kanozawa, who claims that the poor economic conditions and short life expectancy in many developing countries can be explained by low IQ.

The economic historian Richard Wilkinson has argued that economic inequality leads to shorter life expectancy because being at the bottom of the social pile puts people under prolonged stress. But Kanazawa rejects this hypothesis. He argues his data show that once population IQ is taken into account, a country’s average life expectancy is no longer related to economic development and inequality. Indeed, he found IQ was between seven and eight times more strongly related to life-expectancy than were measures of income inequality.

Since Kanazawa also argues that IQ is genetic, there seems to be little chance of escape from this cycle of poverty and death. Not having read the article, I can only point out that the logic appears to be a bit circular: wouldn’t the evidence which suggests that low IQ causes poverty also suggest that poverty causes low IQ? And what of the considerable evidence that IQ can be improved by education? What of the research suggesting that self-discipline is more important than IQ?

In Kanazawa’s favor, I should also point out that similar arguments can be made to contradict Wilkinson’s claim that low IQ is caused by poor economic conditions.


  1. #1 Sandeep Gautam
    October 16, 2006

    Kanazawa definitely ignores the accumulating evidence that poor socio-economic conditions are a cause rather than effect of low IQ. I have attempted to provide a more reasoned analysis of the facts he presents.

  2. #2 Chris
    October 16, 2006

    I don’t see how you could ever hope to disentangle the causes from the effects at the level of a whole society (not even mentioning third factors like climate or endemic diseases). Most likely, low IQ causes poverty *and* poverty causes low IQ – but since both effects are statistical, there is a way out for at least some people. (You can’t be born much poorer than Frederick Douglass – anyone want to accuse him of low IQ? Of course he’s an outlier, but the existence of outliers is part of my point.)

    You could perhaps rule out the genetic hypothesis by studying international adoptions of infants, though. If they clearly perform as well as the adoptive parents’ demographic and not their genetic parents’ demographic, genetic factors would be ruled out; unfortunately, the reverse is not true, because they weren’t adopted at conception and prenatal conditions (especially the health and nutrition of the mother) could have quite an impact. You would probably end up only being able to say that about X% of the difference was due to genetic plus prenatal environmental factors and the remainder due to postnatal factors (parenting, postnatal nutrition, education, endemic disease, etc.)

  3. #3 Gordon Worley
    October 17, 2006

    From the article description, this sounds as if the author confused correlation with causation, in which case the findings may be solid by the conclusions are not. Why must it be this direction of causation, rather than the opposite or some other, confounding factor?

  4. #4 Stephen
    October 19, 2006

    This argument has been used in the US to promote blatant racism. The trouble is that when education comes to poor families, the measured IQs shoot up to those of wealthier people.

    There was even the argument that smart people should have more kids, because otherwise the poor stupid people will outnumber the smart ones. They advocated sterlizing the poor.

    Fully half of all people have above average IQs. (The glass is half full.)
    Half of all people have below average IQs. (The glass if half empty.)
    Everyone of below average IQ should be sterilized. (Far from the glass is twice as big as it needs to be, this is blatant bigotry.)

    All analogies eventually break down. If one didn’t, it wouldn’t be an analogy, it’d be the thing you were describing.