POLYMORPHISM
| Collection | International Encyclopedia of Systems and Cybernetics |
|---|---|
| Year | 2004 |
| Vol. (num.) | 2(2) |
| ID | ◀ 2582 ▶ |
| Object type | Discipline oriented, General information |
The occurence of different basic characters, forms or types in a population.
The concept comes from population genetics, but has a more general scope.
Polymorphism may be transient when the environment acts as a filter and eliminates some variants. It may be permanent if some variety is necessary for a better global adaptation of the population to a fluctuating environment.
According to R. LEVINS: “Polymorphism contributes to the fitness in two distinct ways. If the environment heterogeneity is large compared to the tolerance of the individual (if the environment consists of several discrete niches, in which different phenotypes are optimal, or if it is distributed bimodally about modes which are sufficiently far apart compared to the tolerance), a certain phenotypic heterogeneity is advantageous as a 'mixed strategy' in conditions of temporal fluctuations.
- “Regardless of whether this first type of polymorphism is desirable, genetic heterogeneity is necessary for any response to selection. The response to selection is advantageous if the environment is sufficiently strongly autocorrelated” (1961, p.38).
Polymorphism guarantees that at least some individuals in a population will adapt even to strong environmental variations. It corresponds to ASHBY's variety.
The suppression of polymorphism as for example in excessive selection in plants, leading to mono-cultivation, may be risky. Inversely, the existence of polymorphism, for instance in a population of pests, explains the progressive appearance of varieties resistant to chemicals.
Conditions analogous to polymorphism also seem to exist in animal behavior and in human social and cultural life.
See also
Diversity