Among the things most characteristic of organisms--most distinctive of living as opposed to inorganic systems--is a sort of directedness. Their structures and activities have an adaptedness, an evident and vital usefulness to the organism. Darwin's answer and ours is to accept the common sense view...[that] the end ("telos") [is] that the individual and the species may survive. But this end is (usually) unconscious and impersonal. Naive teleology is controverted not by ignoring the obvious existence of such ends but by providing a naturalistic, materialistic explanation of the adaptive characteristics serving them. [Book review in "Science," 1959, p. 673.]