Why is the heritability of adaptations generally zero?
One often reads in the paper that researchers have discovered the gene for homosexuality or shyness, or, more generally, that some trait is ‘heritable’. Heritability means that variation in some trait (like the presence or absence of homosexuality) is correlated with genetic variation (e.g., the presence or absence of some gene). It is a common mistake to assume that if a trait is heritable, it is adaptive. The opposite is generally the case! Adaptations evolve by the differential reproduction of alternative alleles. Novel alleles arise by mutation. If the phenotypes associated with these novel alleles interact with aspects of the environment in such a way as to gain a reproductive advantage over phenotypes associated with other alleles at the same locus, the novel allele will (with some exceptions discussed below) go to fixation–that is, its frequency in the population will be 100%. Heritability is the proportion of variance in a phenotypic trait that is accounted for by genetic vari
