But in evolution, the sensible definition of “significant” is “having a significant effect on allele frequency”, and that’s not arbitrary. The point is that any significant truncation is not a stable equilibrium condition. Significant truncation implies a significant effect on allele frequency, which moves the distribution in the next generation until the truncation is no longer significant. So under constant selection pressure (a stable environment), you will generally see an approximately normal twotailed distribution.
Now, this is biology, so of course it’s not a perfect model, there will be second order effects, some traits may have genes with larger effect than most, the extreme tails will not be normal, etc. But the basic first order model that quantitative traits controlled by small contributions from many loci will have an approximately normal distribution has a sound theoretical foundation and good empirical support.
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Last edited by Riemann; 11122018 at 11:24 AM.
