The environment and the genotype in polymorphism

Abstract

It is argued that polymorphism is a useful broad term applicable to all forms of discontinuous variation affecting the same stages of development within populations. This unqualified term is particularly applicable when the fact of variation is known, but its causation is not known. The term “genetically determined polymorphism” is proposed for those polymorphisms where the genotype is paramount in morph determination, and where the environment is of little, if any importance (e.g. blood groups). Where the environment interacts with the genotype to elicit a particular morph the term “environmentally cued polymorphism” is apposite. Genetically determined polymorphisms result from discontinuously distributed, but continuously active genetic material, whilst environmentally cued polymorphisms appear to depend on universally distributed, but differentially active genetic resources. Environmentally cued polymorphism produces morphs congruent with current ecological conditions, and in fluctuating or alternating environments it avoids the worst effects of selection for the previously existing conditions. In fluctuating environments genetically determined polymorphism is a particularly costly method of achieving adaptation.