Is the ethical debate over killing and farming animals only a recent thing? Or did it span back further?

Although there are some of the probably older traditions around the world (like ancient Indian jainism, which advocated a path of non-violence towards all living beings, animals and humans alike) I'll limit my answer to ancient Greek philosophy – field of my academical interest.

We'll start with Pythagoras (Samos, c. 570 – c. 495 BC), presocratic philosopher who, same as Socrates, didn't write down his thoughts, but had a faithful bunch of students and followers to whom we own his historical record. Dicaearchus (Aristotle's pupil) wrote how Pythagoras': „most universally celebrated opinions, however, were that the soul is immortal; then that it migrates into other sorts of living creature [...]“

Now in this, his doctrine of the transmigration of souls (metempsychosis), lies bio-ethical stance on killing animals. For one more example of the metempsychosis doctrine we can observe quote from Empedocles (c. 490 – c. 430 BC): „For already have I once been a boy, and a girl, and a bush, and a fish that jumps from the sea as it swims.“

The important part of this doctrine is that it proclaims personal survival of bodily death. By Xenophanes' writing considering this context, Pythagoras even recognized the dog as one of his late friends. Now, if I held this opinion, we can see how easy it would be for me to defend non killing and farming animals – how can I eat a chicken, if there's possibility that that chicken was my mother?

Both Empedocles and Pythagoras were vegeterians. By Empedocles' surviving fragments, which are concerned with „not killing living creatures“, we learn that we are enjoined to abstain from „harsh-sounding bloodshed“, to avoid sacrifice and moreover, we must not eat meat, beans or bay leaves. As explained, the sheep you slaughter and eat was once a man, and once, perhaps, your son or your father. That said, to avoid patricide and filicide you must avoid all bloodshed.

Pythagorean school was an interesting mix of philosophy and mysticism, with an unique set of rules, such as not taking roads which public uses (out of fear of being defiled by the inpure, as Aristotle explains), dietary restrictions, vows of silence for new initiates, etc., and I encourage you to read further on this funky crew.

For now and to conclude, let's jump few centuries forward to confront Empedocles and Pythagoras with Aristotle. Aristotle (384–322 BCE) assigned to men and animals the faculty of sentience (capacity to suffer), but which gives men a title to moral consideration. That means animals don't have rationality or moral qualities which could match ones that we find in humans. He argued how plants are created for the sake of animals, and animals for the sake of men. What he did is establish some sort of hierarchy, taxonomical categorization - scala naturae (or Great Chain of Being) and at the top of that chain are masters who are gifted with rationality – men.

As we can see, Aristotle's position that humans and animals create two opposite moral circles, one rational and one non-rational is directly clashed with Pythagoras' and Empedocles' stance. To further this ancient debate, Aristotle's pupils, Theophrastus (c. 371 – c. 287 BC) argued also for vegeterianism, as he tried to explain how animals can feel same as men do and thus killing them is morally wrong. These are the beginnings of the ethical debate of killing animals in Western philosophy, and further thinkers followed in next centuries – Seneca, Plutarch, Plotinus and Porphyry, to name ancient Roman ones, for example.

Sources:

Jonathan Barnes, The Presocratic Philosophers, Routledge, 1979.

Terence Irwin, The Development of Ethics: A Historical and Critical Study, Oxford, 2007.

Historia Animālium, Aristotle

Robert Audi, The Cambridge Dictionary of Philosophy, Cambridge, 1999.