Sir Francis Galton's (1869/1892) notion of nature versus nurture is a cornerstone of psychology: It was recently featured in two issues of the Monitor (March and April 2004) and was infused throughout the January 2005 issue of the American Psychologist. R. L. Sternberg, E. L. Grigorenko, and K. K. Kidd offered keen insights into the pitfalls in the study of intelligence and race, discerning between folklore and science. Similar scrutiny is needed of the premise underlying these articles: that the nature-nurture paradigm is a scientific fact. Ultimately, the validity of statistical formulae derived from Galton's thesis depends on unproven assumptions. Further, a dimensional ontology allows expansion of the theoretical perspective. The idea that nature and nurture make people who they are is easily distilled into a statistical formula: In terms of variance, "heritability and environmentality add to unity" (Sternberg et al., 2005, p. 53). The first assumption, termed exclusivity, stems directly from that idea: Only nature and nurture make people who they are. This leads to a paradigmatic requirement: No influences exist other than genetics and environment. The second assumption implicit in the body of nature-nurture research, termed universality, is that the paradigm is valid for every human trait studied. A discussion of phenylketonuria is presented as an example of a possible exception to the universality assumption. A third assumption, complementarity, must also be addressed: Nature and nurture constitute a linear dichotomy, even in interaction. As Sternberg et al. (2005) noted, "Heritability has a complementary concept, that of environmentality" (p. 53). This dichotomous structure requires that variation from any other source automatically be included under heritability, environmentality, and/or their interaction, thus precluding its consideration outside of the paradigm (Biddell & Fischer, 1997). In the example of PKU, if heritability is minimized, is environmentality correspondingly increased? However, as mentioned earlier, the ability to choose likely has become the greatest source of variability. A dimensional ontology allows a more parsimonious inclusion of these factors. From a clinician's standpoint, the small arena of choice is likely the most powerful fulcrum available for change. For decades, Galton's (1869/1892) nature-nurture paradigm has anchored psychological research and theory. Though renowned, his idea and its derivations were never scientifically validated. Galton's idea, and all studies based on it, bear reconsideration.