Prompted by the thread on cooked meat and the human evolution to like the smell and taste of cooked meat - I am wondering why some humans became vegetarians / vegans. Specifically:
This might be hard to answer. I think it’s true even today that much of the world’s population has a diet which is mostly or always vegetarian - i.e. meat is an occasional, luxury item, or is not eaten at all. This is basically environmental; once your population/lifestyle is such that you can no longer sustain yourselves by hunting, you feed yourselves through agriculture, and raising meat is generally inefficient in terms of resource utilisation by comparison with raising edible crops, so - especially where populations are dense and/or agricultural resources are scarce - there’s an advantage to a vegetarian or near-vegetarian diet.
That’s quite different, of course, from a vegetarian diet adopted for ethical reasons, but it does encourage the development of ethical vegetarianism, and also of cultural vegetarianism - i.e. you have a vegetarian diet not because you feel a moral obligation but because everyone around you does; it’s what you’re used to; that’s the food you know how to prepare; etc.
The result of all this is that if you look at vegetarianism in, say, Indian history it can be hard to say whether it’s a practical choice, the logical stance given social and environmental conditions, a stance adopted for ethical reasons or simply a cultural habit.
But, having said that, Jainism goes back to at least the fifth century BCE, and espouses a strictly vegetarian diet for explicitly ethical reasons. So that might be a candidate which fits your criteria.
This raises an interesting issue. With Jainism being such an old religion and having been practiced in the same area for millennia, there are probably some people in India whose ancestors have practiced vegetarianism for the over fifty generations. Have there been any medical studies conducted on these people to see what the effects of this have been?
Well, I think you have two problems there. The first is that, while Jainism enjoins a strictly vegetarian diet, how can you be sure that someone’s ancestors have faithfully observed this injuction for the past fifty generations? (Compare Chrisitianity’s injunctions to sexual continence and marital fidelity with how people have actually lived over the years, and you see what I mean.) The other problem is that your control group (non-Jains living in the same society) have also largely followed a mostly vegetarian diet most of the time.
For one thing, even strict vegetarians are not as strictly vegetarian as they think they are, especially if they consume minimally processed natural foods as opposed to commercially refined ones. “Unintentional entomophagy” is the name for involuntarily eating insect parts as contaminants in other foods. It’s claimed that in fact this is an important source of vitamins in traditionally vegetarian diets (especially rice-based ones), with possible health risks for vegetarians if abandoned in favor of “cleaner”, less insect-nutrient-rich grains.
For another, anecdotal evidence suggests that people from strictly vegetarian Jain families who turn to voluntary meat-eating do not have any more physiological difficulty with it than people of other backgrounds do.
What do generations have to do with it? Diet does not affect your genes. (Well, OK starvation can have epigenetic effects that are felt a generation or two on, but vegetarianism is nothing like being starved.) Any medical effects, good or bad, of a lifelong vegetarian diet are going to be manifest, at full strength, in the first generation to live that way.
¬¬¬¬¬¬¬¬
The ancient Greek Pythagoreans are traditionally held to have been vegetarians (they would not eat beans either, as they thought that the souls of deceased people and animals were given to migrating into beans). Pythagoras is thought to have lived in the late 6th to early 5th century BC. (However, scholars now hold that most of the stories told about Pythagorus and the Pythagoreans in later antiquity are, in fact, extremely unreliable legends, so very little is known for sure about their beliefs and activities, and much of the information you will find online, in textbooks, and even in scholarly books from before the 1970s, is mostly without good foundation.)
I think what Little Nemo had in mind (although I can’t speak for him) is something like the development of lactase persistence in certain human populations within the past 10000 years owing to dairy farming and the advantages it bestows on adults who continue to be able to digest fresh milk.
Of course, strict socially-mandated vegetarianism has probably been around for a much shorter time than dairy farming and may not have been practiced consistently enough to exert any significant evolutionary pressure. But I don’t think it’s an unreasonable speculation to wonder if, say, people from long-term strictly vegetarian populations might have experienced a certain amount of selection pressure in favor of, say, more efficiently extracting from vegetable sources some nutrients that are more easily obtained by non-vegetarians from meat.
However, my speculation about that speculation would be that probably no such changes happened, because it’s really not that difficult to get full nutrition from an abundant and varied lacto-vegetarian diet anyway, so there’s no particular advantage to evolving a way of digesting vegetarian food more efficiently.
people became vegetarians because carrots couldn’t run as fast.
Vegetarian: An ancient word meaning “lousy hunter.” (joke)
On a more serious note, vegetarianism is also found in ancient Greece. It was called ἀποχὴ ἐμψύχων (Greek for abstinence animate, meaning to abstain from eating “animated things”, aka things with a soul). It was practiced by members of the Orphic religion and also by Pythagoras (yes, that Pythagoras, the triangle theorem guy) and his followers, as njtt already mentioned. There are also references to the Lotus Eaters in Homer’s Odyssey.
Wikipedia article on Orphism:
Wikipedia article on Pythagoreans:
Orphism and Pythagoreanism both had fairly similar views and were probably influenced by the other.
The Greek references go roughly back to the same time period as the Indian references, 5th century B.C. or thereabouts.
Please take note of what I said in post #6. Given the current state of scholarship concerning Pythagoras and the Pythagoreans, Wikipedia articles on them (as well as most other web sources) should be treated with even greater caution than usual. (I suspect it is not very reliable about teh Orphics, either, for similar reasons.) The best online source on Pythagoras and the Pythagoreans is undoubtedly The Stanford Encyclopedia of Philosophy, which, unlike Wikipedia, is written by accredited subject experts.