ABSTRACT
The norm of reaction of a genotype is the pattern of the phenotypes that can be realized by placing that genotype in some range of environments. The variation that Darwin perceived was phenotypic; evolution was the process of the conversion of phenotypic variation between individuals into phenotypic variation between populations and species. The transmission of this variation from parent to child was assumed by Darwin and Galton to be blending in character: the expected phenotype of a child was the average of its parents' phenotypes. The theory of selection on the genotype has been most extensively studied under the assumption that the selection is due to differences among genotypes in their ability to survive from birth to adulthood. Unfortunately, rules of transmission for the phenotype are not as simple as Mendel's rules for genetic transmission. Fisher's theory identifies the transmission of genes and phenotypes by taking each genotype to contribute in a precise way to the phenotype.
