Oh, yeah. But I think It is probably true that it is difficult to build a model of a continuous trait in which truncation of one tail does not affect the equilibrium of the other tail.
The more relevant point is additive heritability (aka h^2 or narrow sense heritability. Any model will have some, so my condition of having any is not helpful. But if a trait has a lot, that means the trait is pretty close to counting genes, hence the distribution must be a bell curve. But that doesn’t mean that it is a constraint on models.
The more relevant point is additive heritability (aka h^2 or narrow sense heritability.
Not all traits are additively heritable, e.g., the malaria protection/sickle cell anemia gene, and in particular its not obvious that intelligence is additively heritable. One theory I’ve heard is that things like autism are a result of having too many “intelligence genes”.
Even in the most extreme case of dominance, where H^2 greatly diverges from h^2, the additive heritability is not zero. (But if you had a trait in which heterozygotes were distinguishable from homozygotes, but the two types of homozygotes were not distinguishable, then h^2=0. I know of no such trait.)
Oh, yeah. But I think It is probably true that it is difficult to build a model of a continuous trait in which truncation of one tail does not affect the equilibrium of the other tail.
The more relevant point is additive heritability (aka h^2 or narrow sense heritability. Any model will have some, so my condition of having any is not helpful. But if a trait has a lot, that means the trait is pretty close to counting genes, hence the distribution must be a bell curve. But that doesn’t mean that it is a constraint on models.
Not all traits are additively heritable, e.g., the malaria protection/sickle cell anemia gene, and in particular its not obvious that intelligence is additively heritable. One theory I’ve heard is that things like autism are a result of having too many “intelligence genes”.
Even in the most extreme case of dominance, where H^2 greatly diverges from h^2, the additive heritability is not zero. (But if you had a trait in which heterozygotes were distinguishable from homozygotes, but the two types of homozygotes were not distinguishable, then h^2=0. I know of no such trait.)