On the Relations Between Compositional and Evolutionary Theories

Abstract

On the basis of breeding ratios arrived at as a result of experiments with edible peas, Gregor Mendel concluded that certain ‘differentiating characters’ of the plants were paired with one another in such a way that an individual hybrid plant, though it might possess elements capable of causing either of the observable characters, nevertheless would in such a case manifest only one (the dominant as opposed to the recessive character). Crossing of plants with alternative characters of such pairs, moreover, led him to two fundamental ‘laws’ of heredity:

• (1) Segregation, according to which, in such matings, the members of each pair in one parent separate to unite with a member of the corresponding pair from the other parent; if the parents each have a dominant (A) and a recessive (a) factor of the pair, the offspring may be either AA, Aa, aA, or aa; and those alternatives are equiprobable, so that the observed ratios of dominant to recessive character in the offspring of hybrids will be 3:1.

• (2) Independent assortment, according to which any pair of elements does not affect the equiprobability of alternative combinations of any other pair.