Two key factors combined to doom animals since the beginning of human civilization. First, a perennially angry and vengeful god, manifested through natural disasters and battlefield failures, was requiring constant appeasement through animal sacrifices. Moreover, animal labor was as essential then as the combustion engine and electric power are today. Consumption of animal flesh was rare and associated primarily with hunting and trapping.
Animal sacrifices were practiced on a massive scale by Jews around the Jerusalem Temple, from its construction in 960 BCE to its destruction by the Romans in 70 CE. The increased use of animal flesh for food may well have grown out of the need to dispose of the sacrificial victims’ bodies. However, beginning around 780 BCE, Israel’s later prophets Isaiah, Jeremiah, and Hosea condemned both animal sacrifices and consumption of animal flesh.
Verdamana Mahavira (599-527 BCE), in Northeastern India, founded Jainism and popularized the Sanskrit word “ahimsa,” or harmlessness. He taught that we should not inflict on others suffering that we would not want to experience ourselves. Although this sounds like an early version of the Christian Golden Rule, Mahavira applied it explicitly to both human and nonhuman animals.
The Buddha (566-486 BCE) was a younger contemporary in the same region of India who adopted and taught the principles of ahimsa. Unfortunately, most of the billions of Buddhists living today don’t get it.
Pythagoras (570–495 BCE), the great Greek mathematician, philosopher, and contemporary of the two Indian sages, condemned animal sacrifices and urged his followers to abstain from eating animals. For a couple of millennia, vegetarianism was known as the Pythagorean diet.
Greek philosopher Plato (425-347 BCE) propagated Pythagorean teachings, but his star pupil Aristotle (384-322 BCE) opposed them, proclaiming that animals exist only for the sake of humans.
Two historical factors combined to end most animal sacrifices in the first century of the Common Era. In the year 70, following the Jewish rebellion, the Romans destroyed the temple where sacrifices were held. At the same time, Paul, the chief promoter of Christianity, condemned animal sacrifices as an ingrate affront to a god who gave humanity his only son as a sacrificial lamb to expiate their sins. Many Moslems continue to practice animal sacrifices, particularly in conjunction with their Eid al-Adha festival.
By then, frequent consumption of animal flesh had already become part of social norms, and Jews and Christians adopted different ways of dealing with the associated ethical contradictions with their respective religious precepts.
Jewish sages created the Talmud, a massive manual governing human conduct. It includes elaborate rules of kashrut specifying which animals could be used for food and how they should be treated and killed to minimize cruelty. The vestiges can be found in today’s animal welfare and “humane slaughter” laws.
Paul and Christianity adopted Aristotle’s view that animals were created for human use and required no moral consideration, so using them as food was not an issue. He dismissed the biblical injunctions against cruelty to animals as mere metaphors for our treatment of other human beings. Twelve centuries later, this view of animals was reaffirmed by Christianity’s greatest philosopher Thomas Aquinas (1225-1274).
The use of animals for labor persisted till the invention and application of the steam and internal combustion engines toward the end of the 19th century. The steam engine led to the development of railroads, freeing thousands of horses from long distance transport. The diesel engine freed horses and other equines from farm labor. The gasoline engine displaced horse-drawn city carriages.
Human concern for our treatment of nonhuman animals, championed by the Jewish, Indian, and Greek sages as early as 780 years BCE, laid practically dormant for 24 centuries, until resurfacing in 19th century in England.
[I have abstracted most of this material from the scholarly masterpiece The Longest Struggle (2007) by historian Norm Phelps.]