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Cavities, Fuel-Efficiency, and IQ Variation

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  • Russell Johnston
    A recent University of North Carolina at Chapel Hill study coordinated by Dr. David H. Overstreet, associate professor of psychiatry at the UNC-CH School of
    Message 1 of 1 , Nov 24, 2000
      A recent University of North Carolina at Chapel Hill study
      coordinated by Dr. David H. Overstreet, associate professor of
      psychiatry at the UNC-CH School of Medicine and a member of Skipper
      Bowles Center for Alcohol Studies showed "a strong correlation
      between men's preference for sweet tastes and whether their twin
      brothers liked sweets too." (It also suggested a correlation between
      alcoholism and a preference for sweets.) Preliminary results of the
      continuing research, that included 19 pairs of twins, were presented
      Nov. 6, 2000 at a Society for Neuroscience meeting in New Orleans.
      (See news article at: http://www.eurekalert.org/releases/unc-tss110300.html)

      Meanwhile the BBC is reporting that an American team headed by
      Professor Robert Plomin may have already zeroed in on the few genes
      responsible for IQ variation in a Tuesday, 8 August, 2000 article
      entitled "Genius of Genes". "The researchers, working for the US
      National Institutes of Health, analysed the DNA of 200 of the
      brightest kids in America and compared them with the genetic material
      from ordinary children." Although what the genes do isn't known the
      BBC article theorizes that the genes may turn out to "help make nerve

      Now for some thorough speculation, on my part, before it's too late
      to embarrass myself:

      That first study reminds me of a stray fact I stumbled over many
      years ago in a popular work on Psychology by the somewhat
      controversial Dr. Hans Eysenck, which might be of relevance to the
      second. If I remember correctly the story he told there, during the
      Second World War, everyone entering the U.S. Army was given an IQ
      test. Someone who knew statistics and didn't want to end up at the
      front busied himself for years hand-calculating correlations between
      all the variables in the induction data, looking in particular for
      relationships to IQ scores, just to keep themselves busy with
      clerical work and well away from the firefights. Eysenck dismissed
      out of hand the rather startling result - the highest correlation
      found was a very strong .63 between an inducted soldier's number of
      fillings and IQ! And this from a truly huge sample.

      Somehow, Eysenck was utterly unimpressed, concluding that this only
      proved how worthless empirical investigations could be in the wrong
      hands. Not a very scientific attitude to my mind, then or now. But
      here's some speculation that might make sense of that remarkably
      statistically significant result, obtained from millions: just maybe
      what's most clearly inheritable about intelligence, and responsible
      for most of the present variation - is how much of a gas-guzzler the
      brain is tuned to be. After all, the brain uses up about 20% of the
      glucose/energy of the body as a whole, I believe - a very substantial
      amount that is disproportional to its weight. In more traditional
      circumstances when food shortages were predictable hurdles to
      survival, having a brain with better glucose mileage which just
      sipped glucose might have an obvious evolutionary advantage. Of
      course, such energy efficiency is not of great practical use anymore
      in first world nations, at least, nor has this been the case for
      generations. It seems reasonable to me to suppose that the more you
      burn, the more you'll yearn - the more likely you'll be seeking out
      readily available energy in carbohydrates, including sugars like
      sucrose that are responsible for cavities. Just to fill this out a
      little, sucrose is especially attractive to the mutans bacteria
      responsible for cavities, and sucrose releases it's energy very
      quickly compared to, say, fructose (fruit sugar). Also, cavities are
      most closely correlated with the frequency of sugar intake
      (particularly sucrose), not simply quantity. To cite anecdotal
      evidence: at Sandia Labs the carbohydrate consumption per capita by
      researchers is said to be extremely high, leaning towards frequent
      snacks such as pop and chocolate bars that are loaded with sucrose.
      The high-powered brains there, at least, would seem to be gas-

      Against this, it could be argued that those who have high IQs are
      therefore given jobs that demand more thinking, and who then turn
      into heavy fuel-burners, in which case no simple genetic difference
      could be expected to be directly responsible for the variation in IQ
      between humans. But what of manual labor? Does mental activity
      require more frequent or more available energy sources than muscular
      effort - and therefore lead to more cavities? Possibly there's a
      difference, not so much in the quantity of energy and fuel required
      for heavy thinking, as the kind and frequency. Maybe Stevedores ate
      quantities of more complex carbohydrates, less frequently.

      Of course there are other explanations. Maybe wealth correlated
      highly with being able to purchase both books and dental services
      back in 1940, etc. And whether alcohol fits into any of this I'm
      wouldn't care to guess. Certainly it's an energy source, and burned
      preferentially (thus letting other substances concentrate in the
      blood.) But whether it would be sought out for its value as an energy
      source is another question entirely. If this is so for at least some
      of the population, I suppose it's not impossible that alcoholism
      could turn out to be a side-effect of recent evolutionary trends
      toward greater neural energy use and linked energy-seeking behavior.
      It's hoping for a lot to seek out explanations that simple, even as
      partial explanations, but it might be worth mentioning as an

      I also wouldn't care to speculate whether, if the above is tue, it
      might be that significant gene-frequency change has occurred in some
      populations since the introduction of Agriculture, and perhaps even
      since the agricultural revolutions that accompanied the Industrial
      Revolution in the nineteenth century - thus offering what might be
      taken to be a relatively innocuous explanation of "IQ differences"
      between populations, if there are any to be accounted for. Despite
      some recent studies showing selection acting more rapidly than had
      been thought, that's a very short time span, evolutionarily speaking.
      I suppose it might be thought that the second-best thing to our
      discovering no IQ differences between human populations would be to
      discover that there are such differences, but that their cause is
      trivial, and easily altered if we choose to do some quick human re-
      engineering. But I'm not getting so far ahead of the field that I'm
      saying this is so, or any remedies desirable.

      If all this rank speculation holds, it might even be that increasing
      fuel consumption is a fairly simple tweak, perhaps just one gene (or
      any one of several). For future generations, this might be an easy
      way to dramatically alter human beings and society as a whole in
      train. I'm not suggesting that such tinkering should happen: although
      as a "gas guzzler" myself, the prospect of a world teeming with
      chocoholics grubbing for more sweets seems pretty normal to me - for
      all that it may make Lord Winston (who recently called for critical
      discussion of human re-engineering) shudder.

      That's a whole lot of airy speculation to be tagged onto one article
      about the genetics of sweet-craving, and a hint from a gene study
      that's not finished, I know. But, if it's any defense, the astronomer
      Kepler was worse still at charging well beyond the available data, to
      name just one miscreant.

      Also, apologies are in order as my citations could obviously use some
      plumping up here - if you know relevant bibliographic details, I'll
      welcome them with gratitude and some shame.

      PS. - It's been a long time since I read Eysenck - if it turns out
      that the .63 correlation was an inverse one, just shoot me.

      PPS. - In "A Neural Basis for General Intelligence." Dr. John Duncan
      of the Cognition and Brain Science Unit of the Medical Research
      Council in Cambridge, England and his colleagues recently reported
      research in Science showing the dramatic importance for IQ-test
      problem-solving of the lateral prefrontal cortex, a small part of the
      brain. I take this to be independent of my speculations, without
      implications either way for the sort of hypothesis I've put forward

      Russell Johnston
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