Published online by Cambridge University Press: 01 April 2022
These days ‘evolution’ is usually defined as any change in the relative frequencies of genes in a population over time. This definition and some obvious alternatives are examined and rejected. The criticism of these definitions points out the need for a more holistic analysis of genotypes. I attempt such analysis by introducing measures of similarity of whole genotypes and then by grouping genotypes into similarity classes. Three sorts of measures of similarity are examined: a measure of structural similarity, a measure of functional similarity and one of relational or historical similarity. The functional approach is shown to be superior and a definition of ‘evolution’ is suggested.
I wish to thank Eric Bush, Dick Lewontin, Ernst Mayr and W. V. Quine for their helpful comments on earlier drafts of this paper. Thanking them does not imply that they agree with anything I say. Also the referee comments from this journal have led to substantial improvements in the paper.