Historically speaking, few scientific theories have exercised a greater appeal to ethical thinkers than the Darwinian theory of evolution with its attendant notions of "fitness" and "adaptation." Ethical theorists in both the Utilitarian and Pragmatist traditions have seen in it a scientific support for the contention that some forms of behavior, are preferable to other forms of behavior.' At the same time, there has never been any shortage of thinkers who are quite willing to call our attention to the weaknesses of the so-called evolutionary approach to ethics. These men have pointed out quite effectively that equating the fitness of a mode of behavior with its moral value depends upon some previous value judgments.2 That is to say, one must first have assented to the proposition "Adaptation is a value" before one can assent to the proposition "This mode of behavior is valuable because it is adaptive." One can hardly argue with such observations, since they must of necessity apply to any nontautologous value statements. Yet the fact remains that it is precisely the nontautologous value statements which are of practical interest to men. In the final analysis, it may well be the case that a logical justification of nontautologous value statements is impossible. Given this situation, however, at least three courses of action remain open. One is to refrain from any nontautologous value statements for fear of being accused of having committed the naturalistic fallacy. Another is to dismiss arbitrarily the naturalistic fallacy as a pseudoproblem. The former course of action would reduce ethical discourse to a series of vacuous assertions. The latter would ignore what appears to be the positive contribution of the notion of the naturalistic fallacy, namely, the realization that all synthetic value statements are based on certain unstated assumptions involving value judgments. The third alternative is to discern the evaluative assumptions underlying any given synthetic statement and to try to build a case for the general applicability of these evaluative assumptions. I propose to follow this third course of action here with specific reference to the evaluative assumptions underlying the use of adaptation as a normative principle. This will require a three-part analysis of the problem in question. First, we shall determine the meaning of the term 'adaptation' within the context of modern evolutionary theory. Second, we shall have to determine the evaluative assumptions underlying the ascription of value to adaptation thus understood. Having resolved these issues, we will then be in a position to determine just how strong a case can be built in favor of the general applicability of these assumptions.