Running Head: Assumptions of nature-nurture




Examining Unproven Assumptions of Galton’s Nature–Nurture Paradigm


Charles L. McLafferty, Jr., PhD

Charlottesville, Virginia 22903


An earlier version of this comment was published in American Psychologist in February, 2006.
Robert Sternberg's response may be found here (last paragraph).
Please contact the author if you need to cite this unpublished revision.



Examining Unproven Assumptions of Galton’s Nature–Nurture Paradigm



Sir Francis Galton’s (1892) notion of nature vs. nurture is a cornerstone of psychology. It was featured prominently in the March and April, 2004 issues of the Monitor and infused throughout the January, 2005 issue of American Psychologist. Sternberg, Grigorinko and Kidd (2005) offer keen insights into the pitfalls of the study of intelligence and race, discerning between folklore and science. Similar scrutiny is needed to examine the premises of such studies, which imply that the nature-nurture paradigm is a scientific fact. This article challenges three assumptions underlying Galton’s thesis and offers a dimensional ontology to expand the theoretical perspective.

The first assumption, termed unitivity, is based on the idea that “heritability and environmentality add to unity” (Sternberg et al., 2005, p. 53). That is, only nature and nurture make us who we are. Thus variability from any other source must be incorporated into heritability, environmentality and/or their interaction, and therefore precluded from consideration outside of the paradigm.

The second assumption is related to the first. Unidimensionality refers to the concept that nature and nurture are complementary to each other, constituting a linear dichotomy. As Sternberg et al. (2005) note, “heritability has a complementary concept, that of environmentality” (p. 53). Conceptually, genetic and environmental influences constitute extremes of a continuum, a theoretical line that represents influences and interactions of both factors. For the variation of nature and nurture to be additive, they must be measured in similar units or be complementary parts of a whole.

The third assumption is unspoken. Universality requires that the nature–nurture paradigm be valid for every trait studied. 

These assumptions are required in the example of phenylketonuria (PKU), the inability to metabolize phenylalanine. Decades ago, PKU was purely heritable, resulting from an unknown genetic deficiency. Then a scientist discovered its mechanism and prescribed a palliative diet deficient in phenylalanine. PKU is regularly cited as exemplary of nature–nurture interaction (e.g., Sternberg et al., 2005). As will be demonstrated, it also illustrates violations of all three assumptions.

Galton’s (1892) postulates can be addressed through the use of a dimensional ontology, which allows a more parsimonious understanding of human development. Viktor Frankl (1967) noted that the person lives in three interpenetrating dimensions: soma (the physical body), psyche (the emotions and intellect), and the noëtic (the soul). The noëtic dimension includes free will, responsibility, choice, spirituality, and the unique meaning capacity of Homo sapiens. While humans share soma and psyche with animals, the noëtic dimension is defined as that which differentiates us from animals (Frankl, 1967).

In this ontology, genetic expression and variability is somatic in origin—genes synthesize amino acids, pure and simple. Given that most people today have adequate physiological support for normal genetic function (PKU being a notable exception), nurture has greatest variability in the psyche. From this perspective, nature and nurture are dimensionally different rather than complementary and unidimensional.

This relates to the example of PKU, as science has given the person a choice of whether to follow the diet and thus ameliorate the symptoms. The existence of another factor means that nature and nurture are not unitive. The discovery of PKU’s cause has virtually eliminated heritability, but the variability that has increased as a result has been choice, not environmentality. Choice creates a multivariate relationship between nature, nurture and that which chooses. In this respect, nature and nurture are no longer additive and unidimensional. This single exception also invalidates the universality assumption. By extension, on that theoretical day when the human genome is completely understood, Galton’s (1892) theory will be refuted: Scientists will have maximized human choice while minimizing adverse aspects of genetic inheritance.

Theorists have proposed factors that operate in conjunction with genetics and environment, such as symbol systems (language, science, math, musical notation) (Gardner, Hatch, & Torff, 1997) and human agency (Biddell & Fischer, 1997; Frankl, 1967). Assuming that animals do not have language, science and math, nor the “tiny arena of choice” (Frankl, 1967) and free will needed for agency, these distinctly human variables are noëtic. How do they affect nature-nurture research?

Studies of twins regarding language development and IQ invariably involve the measure of noëtic symbol systems, using the manipulation of language and/or representations of math or logic. Research regarding substance abuse involving twins ignores the noëtic dimension. For example, the most successful treatment involves 12-step programs that invoke a “Higher Power” to strengthen the ability to choose. Twin studies of career selection assume nature and nurture alone determine choice, precluding the Jungian sense of “finding one’s calling.” For each of these fields of study, the noëtic dimension is a confounding variable, its variability subsumed into genetic and/or environmental components.

From a clinician’s standpoint, the “tiny arena of choice” is likely the most powerful fulcrum available for change. The healer’s role is arguably to help the client discover and develop a sense of agency capable of harnessing and transcending nature and nurture. With choice comes responsibility and the realization of freedom, which cannot occur without meaningful and purposeful options. Indeed, it is through exercising our ability to choose that we become fully human (Frankl, 1967). Galton’s (1892) paradigm ultimately assumes that the person has no true freedom. To rephrase Frankl (1967), nature and nurture represent our fate, while the noëtic represents our capacity to take a stand towards that fate.

For over a century, Galton’s (1892) nature-nurture paradigm has anchored psychological research and theory. Though renowned, his idea and its derivations were never scientifically validated. Examination of assumptions of unitivity, unidimensionality and universality indicate that Galton’s idea, and all studies based on it, bear reconsideration. Inclusion of the noëtic dimension and its intercourse with genetics and environment allows the researcher to consider the person in studies of human development.

It is time for a new paradigm: Nature, nurture, and the noëtic.





Biddell, T. R., & Fischer, K. W. (1997). Between nature and nurture: The role of human agency in the epigenesis of intelligence. In R. J. Sternberg & E. Grigorinko (Eds.), Intelligence, heredity and environment (pp. 193-242). Cambridge, England: Cambridge University Press.

Frankl, V. E. (1967). Psychotherapy and existentialism. New York: Washington Square Press.

Galton, F. (1892). Hereditary genius: An inquiry into its laws and consequences (2nd ed.). New York: MacMillan. Retrieved November 22, 2005 from (Original work published 1869).

Gardner, H., Hatch, T., & Torff, B. (1997). A third perspective: The symbol systems approach. In R. J. Sternberg & E. L. Grigorinko (Eds.), Intelligence, heredity and environment (pp. 243-268). Cambridge, England: Cambridge University Press.

Sternberg, R. J., Grigorinko, E. L., & Kidd, K. K. (2005). Intelligence, race, and genetics. American Psychologist, 60, 46-59.