Diogenes Laertius Vitae philosophorum 7.1.107

[107] Again, of things preferred some are preferred for their own sake, some for the sake of something else, and others again both for their own sake and for the sake of something else. To the first of these classes belong natural ability, moral improvement, and the like; to the second wealth, noble birth, and the like; to the last strength, perfect faculties, soundness of bodily organs. Things are preferred for their own sake because they accord with nature; not for their own sake, but for the sake of something else, because they secure not a few utilities. And similarly with the class of things rejected under the contrary heads.

Furthermore, the term Duty is applied to that for which, when done, ¹ a reasonable defence can be adduced, e.g. harmony in the tenor of life’s process, which indeed pervades the growth of plants and animals. For even in plants and animals, they hold, you may discern fitness of behaviour.