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1869[evol-psych] Re: Iq" genetic or environmental?

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  • Peter Kabai
    Dec 3, 1999
      > Mark Macnair wrote:
      > The standard model is additive:
      > > P=A+D+E+G*E+I etc
      > I guess explanation of why it has to be multiplicative is
      > not sufficient. Perhaps someone can explain why it has to
      > be additive.

      This basic model is additive, because variances are additive. Quite simple.
      Realistic models are far more complicated than the basic model, mainly
      because the interactive variance cannot be neglected in most cases.

      The interpretation of heritability is also simple: the fraction of genetic
      variance (specifically, the additive variance in the narrow sense of
      heritability) of the total variance in a given population for a given trait
      measured in the given way. So when discussing what heritability really means,
      besides being critical about the methods of measuring the trait, one also
      should keep in mind, that the estimate is restricted to the population in
      which it was measured.

      Heritability of the eye colour is zero in a population of individuals all
      having brown eyes (or blue for that matter). Of course we all know, that the
      colour of our eyes is pretty much controlled by our genes. We would know
      that, even if there was no variation in eye colour, because we know precisely
      how the specific genes act. Learning about the action of the genes give a
      clue to the mechanism, while heritability estimates are purely descriptive.

      There is hope (or worry) that combining neurobiology and genetic data the
      normal variation in IQ will be explained on the level of mechanism.

      Cheers, Peter Kabai
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