According to the ‘first law’ of behavior genetics, ‘All human behavioral traits are heritable.’ Accepting the validity of this first law and employing statistical methods, researchers within psychology, sociology, political science, economics, and business claim to have demonstrated that all the behaviors studied by their disciplines are heritable—no matter how culturally specific these behaviors appear to be. Further, in many cases they claim to have identified specific genes that play a role in those behaviors. The validity of behavior genetics as a discipline depends upon the validity of the research methods used to justify such claims. It also depends, foundationally, upon certain key assumptions concerning the relationship between genotype (one's specific DNA sequences) and phenotype (any and all observable traits or characteristics). In this article, I examine—and find serious flaws with—both the methodologies of behavior genetics and the underlying assumptions concerning the genotype–phenotype relationship. WIREs Cogn Sci 2017, 8:e1405. doi: 10.1002/wcs.1405This article is categorized under: Cognitive Biology > Genes and Environment Neuroscience > Genes, Molecules, and Cells