It is a well-known feature of Aristotle’s biology that he resorts to the analogy with human art to explain the concept of final causality operative in living things. In this Aristotle’s theory of biology is explicitly anti-Empedoclean: whereas for Empedocles a randomly generated animal part is preserved if it happens to suit an expedient function, for Aristotle the formal nature produces an animal part with a useful function in view. In this article, by contrast, I focus on those cases in (...) Aristotle’s biology in which nature adapts an apparently purposeless part to some useful function. I argue that such cases not only indicate a partial return of Empedocles’ logic of generation but are also thought by Aristotle by analogy with human prudence. To consider Aristotle’s account of nature as prudent is not only to disclose a hitherto underappreciated aspect of his biology but also to gain a more comprehensive understanding of prudence in his ethics. (shrink)