We hear almost daily reports of new studies that weigh in on the question of “nature versus nurture”—nature trumps nurture when it comes to criminality, or parenting matters more than genes when it comes to intelligence. Why do people care about nature versus nurture? One reason has to do with understanding: investigating the nature and nurture of a trait like intelligence helps to understand what contributes to its development and variation.

Another reason has to do with intervention: assessing whether nature or nurture contribute more to a trait like intelligence directs efforts to increase it at either genes or the environment. There is a long history of assessing whether traits are the result of nature or nurture, with the hope being that getting answers will increase understanding and direct interventions. Indeed, much of eugenics was organized around the idea that traits are primarily the result of nature, and so interventions should be targeted at increasing the prevalence of genes associated with traits deemed desirable and decreasing the prevalence of genes associated with traits deemed undesirable. The “nature versus nurture” dichotomy is gradually being replaced by a realization that both are essential and inextricably intertwined.

Francis Galton: Father of “Nature Versus Nurture” and Eugenics
Francis Galton (1822-1911), a cousin of Charles Darwin, is credited with first envisioning a science of nature versus nurture. (Interestingly, he was not the first to coin the nature/nurture alliterative phrase; in Shakespeare’s The Tempest, Prospero described Caliban as “a devil, a born devil, upon whose nature/Nurture can never stick.”) For Galton, the question of nature versus nurture was of interest in part because it contributed to understanding where human traits of interest came from. To determine whether heredity or environmental exposures contributed more to traits like criminality or intelligence, Galton developed several methodologies to answer the question. First, he made use of family studies; in Hereditary Genius, Galton collected data on generations of judges, military commanders, and scientists and concluded that these eminent figures were confined to a relatively small number of families. Galton also pioneered the use of twin studies, examining the results of identical twins reared together or apart and comparing twins to other siblings.

Galton was also interested in the nature/nurture question because he thought an answer to it could be used to guide interventions in the world. For Galton, the interventions came in the form of eugenics—a “science which deals with all the influences that improve the inborn qualities of race.” Eugenics, meaning “good birth,” was Galton’s vision for a science that increased the prevalence of traits deemed desirable and decreased the prevalence of traits deemed undesirable (the former is considered the positive form of eugenics, while the latter is the negative form of eugenics). Galton believed that his family studies and twin studies pointed to nature trumping nurture when it came to traits such as criminality and intelligence, and so he envisioned eugenics as a scientifically-guided social program which would encourage more intelligent and less criminal people to marry and breed more, while less intelligent and more criminal people would be encouraged to marry and breed less.

Nature Versus Nurture after Galton
Galton died in 1911, but questions about nature versus nurture and efforts to use the answers to intervene in the world persisted. Throughout the twentieth century, human geneticists continued to undertake family and twin studies (as well as adoption studies, which compared adopted children to children raised by their biological parents). When the science of eugenics fell out of fashion in the mid-twentieth century, it was replaced by fields such as sociobiology and behavior genetics. Sociobiologists studied the biological basis of social behavior, attempting to understand how traits such as altruism or cheating could arise and persist in a population based on their adaptive advantage for the population. Behavior geneticists studied the relative importance of nature and nurture on human traits ranging from criminality and intelligence to schizophrenia and depression, reporting the “heritability of” such-and-such trait or the “genetic variation attributable to” such-and-such trait.

The results of such studies also continued to be used to justify where interventions should be targeted (or not targeted). For example, a debate played out in the 1970s concerning whether the gap in IQ scores between black Americans and white Americans was due to things like discrimination and a history of slavery (i.e. nurture) or due to genetic differences between blacks and whites (i.e. nature). Claims that the IQ gap was due to nature led to calls for the elimination of public funding for social programs designed to educationally compensate minority groups due to the poorer environments they encountered (see Kevles’ book for a history of this episode). Likewise, public controversies have ensued regarding the imbalance of men and women in fields such as science and mathematics. Some have claimed women are less prevalent because they are biologically less suited to these disciplines (an appeal to nature), while critics have countered that the best explanation of the imbalance is an educational environment that steers young girls away from these disciplines (an appeal to nurture) (see Halpern et al.’s article for a review of the scientific literature bearing on this debate). Thus, controversy often follows research on nature/nurture, as arguments for using the results of those studies to shape the world we live in play out in the form of appeals to nature as a biological reality versus appeals to nurture as a thing to be actively shaped.

Moving Beyond the Nature Versus Nurture Dichotomy
Scientists have come to realize that the question of “nature versus nurture” is a false dichotomy. In reality, very few human traits are the result of only genes or only the environment. Rather, the two are inextricably mingled. For example, molecular genetic researched has revealed that genes are turned on and off depending on which environment they are exposed to (a process called “gene expression”). Likewise, individuals with different genes can respond very differently to the same environment; criminality, for instance, has been reported to be more prevalent in individuals with a particular gene but only when those individuals were also exposed to childhood maltreatment (a phenomenon called “gene-environment interaction”). Understanding processes like gene expression and phenomena like gene-environment interaction has implications for intervention; efforts to increase traits deemed desirable or to decrease traits deemed undesirable must target both nature and nurture.

In this way scientists, on the one hand, continue to follow in Galton’s footsteps but also, on the other hand, have taken their own path. Like Galton, scientists continue to ask questions about nature and nurture with the goal of understanding how the world works and a hope of using that understanding to intervene in the world. But unlike Galton, scientists now know that nature and nurture are not mutually exclusive, and so understanding and intervention must take account of both.

-James Tabery

• Conley, James J., 1984, “Not Galton, but Shakespeare: A Note on the Origin of the Term ‘Nature and Nurture’”, Journal of the History of the Behavioral Sciences 20, pp.184-185.

• Galton, Francis, 1869, Hereditary Genius, an Inquiry into Its Laws and Consequences. London: Macmillan.

• Fox Keller, Evelyn, 2010, The Mirage of a Space between Nature and Nurture. Durham: Duke University Press.

• Kevles, Daniel J., 1995, In the Name of Eugenics: Genetics and the Uses of Human Heredity. Cambridge, MA: Harvard University Press.

• Longino, Helen, 2013, Studying Human Behavior: How Scientists Investigate Aggression and Sexuality. Chicago: The University of Chicago Press.

• Moore, David S., 2002, The Dependent Gene: The Fallacy of “Nature vs. Nurture”. New York: Henry Holt/Times Books.

• Panofsky, Aaron, 2014, Misbehaving Science: Controversy and the Development of Behavior Genetics. Chicago: The University of Chicago Press.

• Stotz, Karola, 2008, “The Ingredients for a Postgenomic Synthesis of Nature and Nurture”, Philosophical Psychology 21, pp. 359-381.

• Tabery, James, 2014, Beyond Versus: The Struggle to Understand the Interaction of Nature and Nurture. Cambridge, MA: The MIT Press.

• Wahlsten, Douglas, 1990, “Insensitivity of the Analysis of Variance to Heredity-Environment Interaction”, Behavioral and Brain Sciences 13, pp.109-161.

• Halpern, Diane F., Camilla P. Benbow, David C. Geary, Ruben C. Gur, Janet Shibley Hyde, and Morton Ann Gernsbacher, 2007, “The Science of Sex Differences in Science and Mathematics”, Psychological Science in the Public Interest 8, pp. 1-51.

• Segerstråle, Ullica, 2000, Defenders of the Truth: The Sociobiology Debate. Oxford: Oxford University Press.