Male and female correlations for taster (P.T.C.) phenotypes and rate of adolescent development

Abstract

Growth and development from infancy to age 18 years in tasters and non-tasters of phenylthiocarbamide (P.T.C.) were studied in 50 female and 44 male subjects. Taster girls reached all indices of maturation an average of 3.8 months earlier than non-taster girls. The reverse was true for boys, non-tasters maturing on average 6.2 months earlier than tasters. For both sexes, there was a significant correlation between an overall Maturity Index and P.T.C. sensitivity, positive for girls and negative for boys. Thirty-two of the females and 20 of the males could be classified according to P.T.C. genotype. For these, the onset, midpoint, and end of the pubertal growth spurt was estimated. Heterozygotes reached these points at times intermediate to homozygotes. Taster females preceded non-taster females and non-taster males preceded taster males by about 6 months. The finding of reversed associations between P.T.C. phenotype and maturation in males and females implies that factors underlying the P.T.C. polymorphism may not be confined to mediation through thyroid metabolism, but may also involve other complex pathways of the hypothalamic-pituitary-gonadal axis, particularly those of the sex hormones. The data were examined for evidence of whether or not the findings could be related to a means of maintaining the P.T.C. polymorphism. A significant negative assortative mating pattern was found. This accords with reports from the literature indicating personality differences between early and late maturers and a tendency for spouses to have similar personality characteristics. However, disassortative mating alone could not produce a stable equilibrium. A hypothesis for the maintenance of the P.T.C. polymorphism is developed on the assumption that the timing of puberty is related to reproductive fitness and subject to balancing selection. Heterozygotes for P.T.C. would be at an advantage because they have intermediate maturation times. In this small sample, P.T.C. heterozygotes were also found to produce more offspring than homozygotes.