In this paper I will examine two responses to the argument from marginal cases; the argument from kinds and the similarity argument. I will argue that these arguments are insufficient to show that all humans have moral status but no animals do. This does not prove that animals have moral status but it does shift the burden of proof onto those who want to maintain that all humans are morally considerable, but no animals are.

We live in an age of great scientific and technological innovation, and what seemed out of the question or at least very doubtful only a few years ago, today lies almost within our grasp. In no area is this more true than that of human health care, where lifesaving and life-enhancing technologies have given, or have the enormous potential in the not so distant future to give, relief from some of the most terrible human illnesses. On two fronts in particular, (...) xenograft or cross-species transplantation and genetic engineering of animals on behalf of gene therapy in humans, such relief appears very promising, if not actually on the horizon. Certainly, extensive research work on both fronts is underway both in the United States and abroad. (shrink)

Animal liberation ethics and environmental ethics have recently come of age. Concerning concrete moral rules considered by researchers in these areas there is much consensus. Highly general theories formulated to justify the rules are more problematic. However, the search for such theories may well be misguided.