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1891[evol-psych] Re: Iq" genetic or environmental?

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  • Irwin Silverman
    Dec 4, 1999
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      On Sat, 4 Dec 1999, Peter Kabai wrote:

      > Zilch heritability, however, does not mean that there were no genes
      > involved in the development of such a trait. In a random sample of
      > families not much variation could be found for bilateral symmetry, or
      > the number of eyes, therefore heritability of those traits could not be
      > estimated. On the other hand, genes involved in bilateral symmetry,
      > the formation of eyes etc. have been mapped and their action is pretty
      > well known. Indeed, traits under higher selection pressure
      > tend to be under more precise genetic control and show less
      > "heritability".

      Granted there must be an adequate distribution of a trait
      in order to assess its heritability estimate, but I do not view this as a
      critique of the method where it can be applied. For example, the N for
      schizophrenia in the population is sufficient for heritability estimates to
      be obtained and these stand at present as virtually the sole evidence for
      a genetic influence in the disorder. On the other hand, there are probably
      insufficient cases of Munchausan Syndrome for a similar analysis, but I
      don't see where this impacts in any way on the schizophrenic data.
      Regarding your last point, I have argued also that traits under
      high selection pressure (directional selection in any case) will show less
      heritability. (see my paper on r/k theory in Ethology and Sociobiology,
      1992), maintaining that the high heritability figures for I.Q. reflect, if
      anything, the lesser influence of the attributes measured by I.Q. tests in
      hominid evolution. But again, I do not see that this bears on the
      validity of the heritability measure, properly applied. Heritability is an
      estimate of the relative influences of genetic and environmental factors on
      measureable trait variances in extant populations ... albeit a crude measure
      which will undoubtably, eventually give way to advances in genetics ... but
      the best we have right now and useful in many ways. For example,
      developmental psychologists who follow the prevailing social learning and
      role modeling theories should be very interested in the data on the lack of
      effects of shared environmental effects on personality traits. Piagetian
      scholars should appreciate the data on maturational level differences in
      heritability estimates for specific cognitive capacities, etc ...
      Regrettably the method has become inappropriately entwined in
      contentious sociopolitical issues, whether this is a fault of its users or
      its critics, and when this happens objectivity inevitably goes out of the

      Irwin Silverman
      Psychology Department
      York University
      4700 Keele Street
      Toronto, Ontario M3J 1P3
      Ph. 416-736-2100 x66213
      fax 416-736-5814
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