More from less, increased variance from bottlenecks

I have stated before that additive genetic variance is the relevant component of variance when modeling the response to selection in relation to a quantitative trait. In other words: Response = (additive genetic variance)/(total phenotypic variance) X Selection Consider height, which is about 80% heritable in the narrow sense in modern developed nations. What do I mean 80% heritable in the narrow sense? I mean that 4/5 of the variation in height, which is distributed in a normal fashion, is controlled by additive variation in the genotype. In other words, if I substitute allele 2 for allele 1 it is going to have an effect of deviation z upon the phenotype. What are the other components of variation? Obviously environmental variation. In regards to height we're probably talking about nutrition, but since in modern societies we have something of a nutritionally saturated environment this doesn't really vary too much (if ...