Up to now our discussion has shown that mutations are the source of evolutionary change and progress. However, the elementary process which leads to a specific mutation is fundamentally undetermined. Consequently, deterministic selection theory is not in a position to predict the moment of appearance or the nature of a mutation. It is concerned rather with the higher-order problem of the physico-chemical conditions which have to be fulfilled in order for a mutation to be capable of reflection in macroscopic change. The emphasis here is upon the word “capable”, for the deterministic treatment ignores the fact that the amplification of a mutant is itself subject to statistical fluctuations. Since each mutant first appears as a single copy, fluctuations may be expected to influence its concentration until this reaches macroscopic values. The statement of deterministic theory that every better-endowed mutant Im+1 will certainly assert itself against its master sequence Im is only true in the limit of large numbers of copies.
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