This is a reply to commentaries on the target article (J. C. Wakefield, 1999) on the evolutionary foundations of the concept of mental disorder in defense of the harmful dysfunction analysis (HDA) of disorder. The author argues that the HDA is adequate to explain disorder and nondisorder judgments and is not disconfirmed by any of the claimed counterexamples put forward by the commentators; the commentators' proposed alternatives to the HDA are inadequate to explain disorder and nondisorder judgments; and the concept of natural function is a factual, scientific concept, contrary to K. W. M. Fulford's (1999) claim that it is inherently evaluative. The foundations of the HDA are clarified by providing a black box essentialist analysis (H. Putnam, 1975; J. C. Wakefield, 1997, in press) of the concept of natural function that underlies the concept of disorder.