In 2002, Evolution and Human Behavior published a study purporting to show that the differences in toy preferences commonly attributed to girls and boys can also be found in male and female vervet monkeys, tracing the origin of these differing preferences back to a common ancestor. Despite some flaws in its design and the prima facie implausibility of some of its central claims, this research received considerable attention in both scientific circles and the popular media. In what follows, I survey some of the problems with this study that seem to be characteristic of research into sex differences in a particular research program in evolutionary psychology. I suggest that an epistemology of ignorance is at work that suppresses the methods and insights of an earlier research program, which emphasized the complexity and contingency that ultimately grounds the variety of human behaviors, in favor of one that has been widely criticized as empirically flawed and politically pernicious. I conclude with some speculative remarks on the persistence of this problematic research program in evolutionary psychology.