My point is that ethics is a subject. It is pursued by methods that are continually being developed in response to the problems that arise within it. Obviously the creatures who engage in this activity are organisms about whom we can learn a great deal from biology. Moreover their capacity to perform the reflective and critical tasks involved is presumably somehow a function of their organic structure. But it would be as foolish to seek a biological evolutionary explanation of ethics as it would be to seek such an explanation of the development of physics. The development of physics is an intellectual process. Presumably the human intellectual capacity that has permitted this extremely rapid process to occur was in some way an effect, perhaps only a side-effect, of a process of biological evolution that took a very long time. But the latter can provide no explanation of physical theories that is not trivial. What human beings have discovered in themselves is a capacity to subject their prereflective or innate responses to criticism and revision, and to create new forms of understanding. It is the exercise of that rational capacity that explains the theories.

(T. Nagel, “Ethics as an Autonomous Theoretical Subject,” in Morality as a Biological Phenomenon: The Presuppositions of Sociobiological Research, rev. ed., ed. Gunther S. Stent [Berkeley, Los Angeles, London: University of California Press, 1980], 196-205, at 203-4)