Most philosophers believe that humans have far greater moral worth than nonhuman animals. This consensus position invites the following question: What characteristic or group of characteristics of human beings differentiates us from nonhuman animals so that we have greater moral worth than nonhuman animals? Philosophers have offered a number of characteristics that allegedly show human beings to be superior to nonhuman animals. At the top of the list we find thinking and the ability to be rational. Further down the list (...) we find more subtle abilities, for example, such as the ability to be self- conscious. Neither of these nor a host of other prospects provide an adequate ground for the claim of greater human worth.1 But philosophers attribute one ability to humans, or to most humans, that seems immune to the usual criticisms: the ability to be moral. In this essay I want to explore whether the ability to be moral plausibly makes humans more valuable than nonhuman animals. (shrink)