The Ancient Greek philosopher Pythagoras is best known today for his mathematical theorem, which haunts the dreams of many geometry students, but for centuries he was also celebrated as the father of vegetarianism. A meatless diet was referred to as a “Pythagorean diet” for years, up until the modern vegetarian movement began in the mid-1800s.

While Pythagoras was an early proponent of a meatless diet, humans have been vegetarians since well before recorded history. Most anthropologists agree that early humans would have eaten a predominantly plant-based diet; after all, plants can’t run away. Additionally, our digestive systems resemble those of herbivores closer than carnivorous animals. Prehistoric man ate meat, of course, but plants formed the basis of his diet.

Pythagoras and his many followers practiced vegetarianism for several reasons, mainly due to religious and ethical objections. Pythagoras believed all living beings had souls. Animals were no exception, so meat and fish were banished from his table. Strangely enough, he also banished a vegetable that has a place of honor on most vegetarian menus today, the humble bean. His followers were forbidden to eat or even touch beans, because he thought beans and humans were created from the same material. Fava beans were especially bad, as they have hollow stems that could allow the souls of the dead to travel up from the soil into the growing beans.

While the edict against beans was lifted not long after Pythagoras’ death, his followers continued to eat a meatless diet. His principles influenced generations of academics and religious thinkers, and it was a group of these like-minded individuals who founded the Vegetarian Society in England in the mid-1800s. The virtues of temperance, abstinence and self-control were all tied to vegetarian ideals, while lust, drunkenness and general hooliganism all resulted from a diet too rich in meat products. Notable early vegetarians included Leo Tolstoy, George Bernard Shaw, Mahatma Gandhi and American Bronson Alcott, a Transcendentalist teacher, reformer and the father of “Little Women” author Louisa May Alcott.

It wasn’t until the 1960s that vegetarianism moved into mainstream American life and the movement’s growth picked up speed in the 1970s when a young graduate student named Francis Moore Lappe wrote a book called Diet for a Small Planet. In it, she advocated a meatless diet not for ethical or moral reasons, but because plant-based foods have much less impact on the environment than meat does. Today, many vegetarians refuse meat because of animal rights issues, or concerns over animal treatment, a principle first espoused in Peter Singer’s 1975 work “Animal Liberation.”