Plutarch, De facie quae in orbe lunae apparet
Harold Cherniss and William C. Helmbold, Ed.

What is more, if we are finally to throw off the habits <and> opinions that have held our minds in thrall and fearlessly to say what really appears to be the case, no part of a whole all by itself seems to have any order, position, or motion of its own which could be called unconditionally ‘natural.’ ¹ On the contrary, each and every such part, whenever its motion is usefully and properly accommodated to that for the sake of which the part has come to be and which is the purpose of its growth or production, and whenever it acts or is affected or disposed so that it contributes to the preservation or beauty or function of that thing, then, I believe, it has its ‘natural’ position and motion and disposition. In man, at any rate, who is the result of ‘natural’ process if any being is, the heavy and earthy parts are above, chiefly in the region of the head, and the hot and fiery parts are in the middle regions; some of the teeth grow from above and some from below, and neither set is ‘contrary to nature’; and it cannot be said that the fire which flashes in the eyes above is ‘natural’ whereas that in the bowels and heart is ‘contrary to nature,’ but each has been assigned its proper and useful station. Observe, as Empedocles says,² the nature of ‘Tritons and tortoises with hides of stone’ and of all testaceans, ‘Thoult see earth there established over flesh;’ and the stony matter does not oppress or crush the constitution³ on which it is superimposed, nor on the other hand does the heat by reason of lightness fly off to the upper region and escape, but they have been somehow intermingled and organically combined in accordance with the nature of each.