Ancient origins
Deliberate avoidance of flesh eating probably first appeared sporadically in ritual connections, either as a temporary purification or as qualification for a priestly function. Advocacy of a regular fleshless diet began about the middle of the 1st millennium bc in India and the eastern Mediterranean as part of the philosophical awakening of the time. In the Mediterranean, avoidance of flesh eating is first recorded as a teaching of the philosopher Pythagoras of Samos (c. 530 bc), who alleged the kinship of all animals as one basis for human benevolence toward other creatures. From Plato onward many pagan philosophers (e.g., Epicurus and Plutarch), especially the Neoplatonists, recommended a fleshless diet; the idea carried with it condemnation of bloody sacrifices in worship and was often associated with belief in the reincarnation of souls and, more generally, with a search for principles of cosmic harmony in accord with which human beings could live. In India, followers of Buddhism and Jainism refused on ethical and ascetic grounds to kill animals for food. Human beings, they believed, should not inflict harm on any sentient creature. This principle was soon taken up in Brahmanism and, later, Hinduism and was applied especially to the cow. As in Mediterranean thought, the idea carried with it condemnation of bloody sacrifices and was often associated with principles of cosmic harmony.
In later centuries the history of vegetarianism in the Indic and Mediterranean regions diverged significantly. In India itself, though Buddhism gradually declined, the ideal of harmlessness (ahimsa), with its corollary of a fleshless diet, spread steadily in the 1st millennium ad until many of the upper castes, and even some of the lower, had adopted it. Beyond India it was carried, with Buddhism, northward and eastward as far as China and Japan. In some countries, fish were included in an otherwise fleshless diet.
West of the Indus the great monotheistic traditions were less favourable to vegetarianism. The Hebrew Bible, however, records the belief that in paradise the earliest human beings had not eaten flesh. Ascetic Jewish groups and some early Christian leaders disapproved of flesh eating as gluttonous, cruel, and expensive. Some Christian monastic orders ruled out flesh eating, and its avoidance has been a penance and a spiritual exercise even for laypersons. Many Muslims have been hostile to vegetarianism, yet some Muslim Sufi mystics recommended a meatless diet for spiritual seekers.