 Talk of human nature is a common feature of moral and political discourse among people on the street and among philosophers, political scientists and sociologists. This is largely due to the widespread assumption that true descriptive or explanatory claims making use of the concept of human nature have, or would have, considerable normative significance. Some think that human nature excludes the possibility of certain forms of social organisation—for example, that it excludes any broadly egalitarian society. Others make the stronger claim that a true normative ethical theory has to be built on prior knowledge of human nature. Still others believe that there are specific moral prohibitions concerning the alteration of, or interference in, the set of properties that make up human nature. Finally, there are those who argue that the normative significance derives from the fact that merely deploying the concept is typically, or even necessarily, pernicious.