Abstract The study of psychological gender differences (GDs) originated with the earliest studies linking brain structures to differences in behavior, especially in the area of intellectual performance. These lines of research purported to explain sex differences in behavior by comparing brain structures of men and women that were believed to account for them (Shields, 1975). These inquiries represented one facet of the continuing “nature–nurture” debate over the relative impact of genetic heritage and environmental influences as causes of behavior. Present‐day neuroscience research has found evidence for neural plasticity that supports a biopsychosocial interactionist view, which is gaining acceptance over earlier monocausal models (Halpern et al., 2007). However, in the presence of ideological and political commitments to differing views of “human nature,” debates continue over how much of a difference is a just‐noticeable difference, as this depends on who is doing the noticing, and over what is a functionally important difference, as this depends on the function, its context, and its consequences.