Progression of Animals
Aristotle
tr. A.S.L. Farquharson

"At the beginning of our inquiry we must postulate the principles we are accustomed constantly to use for our scientific investigation of nature, that is we must take for granted principles of this universal character which appear in all nature's work. Of these one is that nature creates nothing without a purpose [ἠ φύσις οὐθὲν ποιεῖ μάτην], but always the best [ἄριστον] possible in each kind of living creature by reference to its essential constitution. Accordingly if one way is better than another that is the way of nature." (704b12-18)

"The reason why snakes are limbless is first that nature makes nothing without purpose, but always regards what is the best possible for each individual, preserving [διασώζοθσαν] the peculiar substance [οὐσία] of each and its essence [τὸ τὶ ἦν εἶναι]...." (708a9-12)

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