Thanks to Dr. Rebecca Raphael for sharing this passage on the teleology of the human ass with me. This is mostly for distraction, but it also functions as a timely reminder of some of the absurd conclusions that can arise from teleological thinking.
Aristotle, Parts of Animals 689b
“A human being is has no tail, but does have buttocks although the quadruped does not. A human being also has legs which are fleshy in the thighs and calves, while all the rest of the animals have fleshless legs—and not only those animals which have live births, but as many of the other animals who have legs—and they are covered with sinew, are bony, and full of spines.
There is one explanation, you might say, for these differences and that is that humans are the only animal to stand upright. So, nature removed some of the fleshy parts from above and transferred the weight below in order to make the upper portions of human beings easier to bear. This is why nature made human butts fleshy along with their thighs and their calves. With the same act, it made the nature of the buttocks useful for taking a break.
For it is not a problem for the rest of the quadrupeds and they do not get tired from doing that continually. This is because they have four supports holding them up, it works the same as if they are lying down.But human beings do not easily remain standing upright: our bodies need rest and need to sit down.
This is why a human being has a fleshy butt and thighs and the same reason why we don’t have tails. All the nutrition which heads that way is spent on butts and thighs. The need and use of a tail, moreover, is negated by having butts and thighs. In quadrupeds and the rest of the animals, the situation is the opposite: because they are like dwarfs, all their weight is centered in their upper parts and it is separated from the lower section. For this reason, they have no butt and have hard legs.
ὁ δ᾿ ἄνθρωπος ἄκερκον μέν ἐστιν, ἰσχία δ᾿ ἔχει, τῶν δὲ τετραπόδων οὐδέν. ἔτι δὲ καὶ τὰ σκέλη ὁ μὲν ἄνθρωπος σαρκώδη καὶ μηροὺς καὶ κνήμας, τὰ δ᾿ ἄλλα πάντ᾿ ἄσαρκα ἔχει, οὐ μόνον τὰ ζῳοτόκα ἀλλ᾿ ὅλως ὅσα σκέλη ἔχει τῶν ζῴων· νευρώδη γὰρ ἔχει καὶ ὀστώδη καὶ ἀκανθώδη. τούτων δ᾿ αἰτία μία τίς ἐστιν ὡς εἰπεῖν ἁπάντων, διότι μόνον ἐστὶν ὀρθὸν τῶν ζῴων ἄνθρωπος. ἵν᾿ οὖν φέρῃ ῥᾳδίως τἄνω κοῦφα ὄντα, ἀφελοῦσα τὸ σωματῶδες ἀπὸ τῶν ἄνω πρὸς τὰ κάτω τὸ βάρος ἡ φύσις προσέθηκεν· διόπερ τὰ ἰσχία σαρκώδη ἐποίησε καὶ μηροὺς καὶ γαστροκνημίας. ἅμα δὲ τήν τε τῶν ἰσχίων φύσιν καὶ πρὸς τὰς ἀναπαύσεις ἀπέδωκε χρήσιμον· τοῖς μὲν γὰρ τετράποσιν ἄκοπον τὸ ἑστάναι, καὶ οὐ κάμνουσι τοῦτο ποιοῦντα συνεχῶς (ὥσπερ γὰρ κατακείμενα διατελεῖ ὑποκειμένων τεττάρων ἐρεισμάτων), τοῖς δ᾿ ἀνθρώποις οὐ ῥᾴδιον ὀρθῶς ἑστῶσι διαμένειν, ἀλλὰ δεῖται τὸ σῶμα ἀναπαύσεως καὶ καθέδρας. ὁ μὲν οὖν ἄνθρωπος ἰσχία τ᾿ ἔχει καὶ τὰ σκέλη σαρκώδη διὰ τὴν εἰρημένην αἰτίαν, καὶ διὰ ταῦτα ἄκερκον (ἥ τε γὰρ ἐκεῖσε τροφὴ πορευομένη εἰς ταῦτα ἀναλίσκεται, καὶ διὰ τὸ ἔχειν ἰσχία ἀφῄρηται ἡ τῆς οὐρᾶς ἀναγκαία χρῆσις), τὰ δὲ τετράποδα καὶ τἆλλα ζῷα ἐξ ἐναντίας· νανώδεσι γὰρ οὖσι πρὸς τὸ ἄνω τὸ βάρος καὶ τὸ σωματῶδες ἐπίκειται πᾶν, ἀφῃρημένον ἀπὸ τῶν κάτωθεν· διόπερ ἀνίσχια καὶ σκληρὰ τὰ σκέλη ἔχουσιν.