Which of the following describes the forces that destroy polymorphism?

The forces that contribute to the destruction of polymorphism, which is the occurrence of different forms or morphs within a population, can be effectively described by the interaction of selection and drift.

Natural selection acts on phenotypic variations within a population, favoring specific traits that enhance survival and reproductive success. This can lead to a reduction in genetic diversity as certain allele frequencies increase while others decrease or vanish altogether.

Genetic drift also plays a significant role, particularly in small populations, where random fluctuations can lead to the loss of alleles simply by chance. This stochastic process can overpower the effects of natural selection, especially when the population size is limited.

Combining selection and drift provides a comprehensive understanding of how these forces can drive a population toward a more uniform genetic makeup, thereby destroying the polymorphism present initially. This dual effect is crucial in evolution, as it highlights how both deterministic (selection) and stochastic (drift) processes influence genetic variation within populations.

In contrast, the other options involve processes that may not directly lead to the destruction of polymorphic traits. For instance, migration introduces new genetic material, while environmental changes can lead to adaptation but don't inherently destroy polymorphism without the accompanying forces of selection and drift.