"In point of fact, as MULLER (1955) notes, the less harmful a mutant, the greater the number of individuals it affects, inasmuch as reproduction remains possible. Thus the total measure of mutational harm is the number of mutations produced, of whatever degree of harmfulness, rather than the damage to any one individual or generation. In a population which, like the human, is not inbred, the generation showing the greatest effect of a mutation should be the first filial one; but the total effect in the posterity, over an indefinite number of generations, is still greater (CROW 1958). This point shall be illustrated in relation to the foreseeable effects of radiation upon descendants of man (see Part 11)."