E.B. Ford worked for many years on genetic polymorphism. Polymorphism in natural populations is frequent; the key feature is the occurrence together of two or more discontinuous forms of a species in some kind of balance. So long as the proportions of each form is above mutation rate, then selection must be the cause. As early as 1930 Fisher had discussed a situation where, with alleles at a single locus, the heterozygote is more viable than either homozygote. That is a typical genetic mechanism for causing this type of polymorphism. The work involves a synthesis of field research, taxonomy, and laboratory genetics.