Just as the differentiation of human beings from other species has traditionally been thought to be based on some common essence or nature, so has the division of humankind into certain groups, in particular, men and women and races, been thought to be based on their distinct natures. There are many similarities between the concepts of human nature, ‘women’s nature’ (what we now call gender) and race, and how these concepts have functioned ideologically: For all three, the traditional idea was that there were fixed, natural essences determining the cognitive, moral, and emotional traits and abilities of the group in question. Some, e.g., Plato, and Herrnstein in recent years, have applied the idea to different social classes as well. I will call this view essentialism, and note that it is compatible with various metaphysical analyses. One could be opposed to metaphysical essentialism, but accept essences in this sense, as, for example, Hume did.