When it comes to sex differences, the overlap between genders, even in terms of anatomical differences, can be quite significant. For instance, the female and male pelvises have different shapes, which can affect how the legs are attached. Yet according to the classic study on pelvises, only 40 to 50% of actual women have a female pelvis as defined in anatomy books; 33% have an “android” or maletype pelvis. How is our ability to make generalizations about the sexes affected by such differences?