Are human genetic processes sufficiently plastic to permit the development of intraindividual flexibility? Before addressing this question it is useful to consider how thoroughly human genetic endowment ensures systematic interindividual differences. Our genetic endowment provides a basis of the uniqueness of each human life and provides substance to the claim that all humans have a unique heredity–environment interactive history (Hirsch, 1970; Lerner, 1976, 1978, 1979; McClearn, 1981). Estimates of the number of gene pairs in humans typically range between 10,000 and 100,000 (Bodmer & Cavalli-Sfarza, 1976; Stern, 1973), and if one considers how much genotypic variability can be produced by the reshuffling process of meiosis occurring with 100,000 gene pairs, then the potential for variability is so enormous that “it is next to impossible that there have ever been two individuals with the same combination of genes” (McClearn, 1981, p. 19).

Indeed, Hirsch (1970) conservatively estimates that there are over 7 × 1017 (70 trillion) potential human genotypes. Bodmer and Cavalli-Sforza (1976) estimate that each human has the capacity to generate any one of 103000 different eggs or sperm; by comparison, their estimate of the number of sperm of all men who have ever lived is only 1024. Thus, considering