Primer The heritability fallacy David S. Moore 1 * and David Shenk 2 The term ‘heritability,’ as it is used today in human behavioral genetics, is one of the most misleading in the history of science. Contrary to popular belief, the measurable heritability of a trait does not tell us how ‘genetically inheritable’ that trait is. Further, it does not inform us about what causes a trait, the relative inﬂu- ence of genes in the development of a trait, or the relative inﬂuence of the envi- ronment in the development of a trait. Because we already know that genetic factors have signiﬁcant inﬂuence on the development of all human traits, mea- sures of heritability are of little value, except in very rare cases. We, therefore, suggest that continued use of the term does enormous damage to the public understanding of how human beings develop their individual traits and identities. © 2016 Wiley Periodicals, Inc. How to cite this article: WIREs Cogn Sci 2016. doi: 10.1002/wcs.1400 INTRODUCTION I f someone were to tell you that research has proven that human intelligence is highly ‘heritable,’ what would you think that means? Most people would probably assume that it means people inherit a signiﬁ- cant percentage of their intelligence directly, via their parents’ genes. In fact, though, the scientiﬁc terms ‘heritable’ and ‘heritability’ actually have very little to do with genetic inheritance. This is confusing, because ‘heritability’ sounds like it means the same thing as ‘inheritability.’ The confusion about what ‘heritabil- ity’ actually measures signiﬁcantly adds to a deep mis- understanding about how, exactly, our genomes contribute to our observable characteristics (see Char- ney, Genes, behavior, and behavior genetics, WIREs Cogn Sci, also in the collection How We Develop). THE APPROPRIATION OF ‘HERITABLE’ For hundreds of years, the word ‘heritable’ was used without confusion as a synonym for ‘hereditary.’ But in the early 20th century, the word was repurposed to represent something new and rather narrow. At that time, geneticists had a strictly deterministic under- standing of how genes inﬂuence the formation of traits. They considered the relationship between genes and the environment to be akin to the relationship between a plant seed and the rain that waters it: Genes were thought to contain speciﬁc, blueprint-like instructions for the formation of traits, whereas the environment provided the nutrients and other salubri- ous conditions that would allow those instructions to unfold. According to this earlier way of thinking, a person’s DNA has speciﬁc instructions for blue eyes, or athletic arms, or a mathematical mind; the environ- ment merely allows for emphasis or de-emphasis of those already-designed traits. (If this sounds familiar, it’s probably because it strongly resembles what many of us were taught about genetics in grade school.) The term heritability was ﬁrst given this new mean- ing in J. L. Lush’ s 1937 book Animal Breeding Plans. 1 In that text, Lush proposed a calculation for what he called ‘heritability’ that neatly codiﬁed the then-popular deter- ministic viewpoint. Because, Lush argued, an animal ’s phenotype (i.e., its observable traits, such as intelligence, height, eye color, etc.) is a function of genetic instructions plus the ﬁnishing inﬂuence of the environment, we should be able to statistically separate the inﬂuence of each. 2 Relying on mathematical guidelines from the geneticist Sewall Wright, Lush proposed that in any given group: Vp phenotypic variation ð Þ = Vg genetic variation ð Þ + Ve environmental variation ð Þ *Correspondence to: David_Moore@pitzer.edu 1 Pitzer College and Claremont Graduate University, Claremont, CA, USA 2 DeLTA Center, University of Iowa, Iowa City, IA, USA Conﬂict of interest: The authors have declared no conﬂicts of inter- est for this article. © 2016 Wiley Periodicals, Inc.