Now if nature makes nothing incomplete and nothing in vain, the inference must be that she has made all animals for the sake of man.
Aristotle, Politics I, 1256b

It would not be especially interesting to know what beasts are if it were not a means of recognizing what we ourselves are.
Étienne de Condillac, Traité des animaux, 1755

In fact if one person is unkind to an animal it is considered to be cruelty, but where a lot of people are unkind to a lot of animals, especially in the name of commerce, the cruelty is condoned and (…) will be defended to the last by otherwise intelligent people.
Ruth Harrison, Animal Machines, 1964

We owe justice to men, and grace and goodwill to other creatures.
Michel de Montaigne, Essais, 1580

The world is not a machine and the beasts are not a product for our own use.
Arthur Schopenhauer, Parerga und Paralipomena, 1851