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1890[evol-psych] Iq" genetic or environmental?

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  • Peter Kabai
    Dec 4, 1999
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      Hi, let me briefly respond to M. Hubey and Irwin Silverman.

      Peter Kabai:
      This basic model is additive, because variances are additive. Quite simple.

      M. Hubey's response:
      THis is backwards. The variances are additive because the model is additive.

      It might be backwards, depending from where one looks at it. However, the basic
      model, analysis of variance was not invented by geneticists. It was just applied
      to a very simplistic model: a number of independent factors affect the trait
      additively. In any such model, the total variance of the sum of independent
      factors equals the sum of the variances of these factors.

      > Peter Kabai: Heritability of the eye colour is zero in a population of
      > individuals all
      > > > having brown eyes
      >
      > Irwin Silverman: This seems pointless - If eyes were all one color then there
      > wouldn't be variance to measure and it would not be a variable.

      Estimating heritability for a trait without variation is indeed pointless. 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".

      I think it is important to know, that IQ even within the "normal" variation has
      measurable genetic variance. Whether it is 0.5 or 0.8 might be irrelevant, once
      we learn more about the mechanism. It might be a long way to go, seems that so
      far we search for the key, where there is light, and not necessarily where the
      key might be.

      I am refering to studies on neurotransmitters involved in learning and problem
      solving or metaanalysis on the correlation of brain size and some measure of
      intelligence or behavioural plasticty.

      Some self criticism here:
      Stewart, M.G., Kabai, P.et al (1996). The involvement of dopamine in the striatum
      in passive avoidance training in the chick. Neuroscience 70:7-14.
      Lefebvre, L., Gaxiola, A., Dawson, S., Timmermans, S., Rozsa, L. and Kabai, P.
      (1998). Feeding innovations and forebrain size in Australian birds. Behaviour,
      135:1077-1097.

      I agree, that questions on mechanim, such as posed by Roger D. Masters on the
      effect of lead exposure are highly relevant (and fortunately not hopeless to
      unswere). Not because the true heritability estimates might be some points lower
      than previously thought, but because learning about the actual effects give a
      clue for intervention on the level of the individual (hope or worry).

      Best wishes, Peter Kabai
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