1869[evol-psych] Re: Iq" genetic or environmental?
- Dec 3, 1999
> Mark Macnair wrote:This basic model is additive, because variances are additive. Quite simple.
> 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.
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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