Adaptation and Natural Selection

Environment of Gene Selection

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If the major drive of evolution is natural selection, as selective gene substitution, how can we take into consideration the complex interaction between a gene and other genes, between a geonotype and phenotypes, between individuals and their surroundings? Williams maintains that this question can be dealt with"without recourse to creative evolutionary forces that would not be predictable outcomes of selective gene substitution." But certainly we have to consider the environment of a gene. Williams' proposal is that we should distinguish three different levels of environment:

The gene is selected through a complex interaction with its environment, which can usefully be considered to include several levels: the genetic, the somatic, and the ecological. (p. vi).

Then, how does this distinction help? The crucial scenario is this:

No matter how functionally dependent a gene may be, and no matter how complicated its interactions with other genes and environmental factors, it must always be true that a given gene substitution will have an arithmetic mean effect on fitnesss in any population. (p. 57)

And discussions on each level follow.

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