Our first ancestor, Australopithecus Africanus, was herbivorous and had a diet consisting of hard, brittle foods like nuts and other foods such as tubers and grasses which dominated their diet.
http://www.physorg.com/news175415022.html
After that, the earliest records of vegetarianism as a concept and practise amongst a significant number of people concern ancient India and the ancient Greek civilization in southern Italy and in Greece. Jain and Buddhist sources show that the principle of nonviolence toward animals and vegetarianism was an established rule in both religions as early as the 6th century BC. The Buddhist emperor Ashoka (304 BCE – 232 BCE) was a vegetarian and a determined promoter of nonviolence to animals. He promulgated detailed laws aimed at the protection of many species, abolished animal sacrifice at his court, and admonished the population to avoid all kinds of unnecessary killing and injury.
In Ancient Greece and Rome, people such as Pythagoras, Plato, Plutarch, Socrates and many others were vegetarians and have many quotes relating to their disgust at the treatment of animals.
Many gladiators were vegetarians as well. They were referred to as hordearii which translate into "Barley Men" because their diet consisted of barley to make them fat so that during fights, fat could be sliced off and entertain the crowd but the gladiator could still fight. The strontium levels in their bones, as well as confirming reports from lunista's from that time period (lunista's are the men who ran the gladiator training schools) about their diet, confirms that many were vegetarians.
http://www.archaeology.org/0811/abstracts/gladiator.html
Humans are not designed to be anything. We have evolved as advanced scavengers that can consume different types of foods and non foods and still derive nutrients from them. Some choose to eat meat, some choose not to, either way a human being can still be healthy and meat is not necessary for the human body.
Deer Hunter: My mistake, I was referring to afarensis (The Lucy species)
http://humanorigins.si.edu/evidence/human-fossils/species/australopithecus-afarensis
Although it states small vertebrates may or may not have been consumed, their teeth indicated the diet I explained above ^ and according to your link, the earliest humanoid was still a vegetarian:
http://humanorigins.si.edu/evidence/human-fossils/species/ardipithecus-kadabba
The majority Gladiators were vegetarian because barley was cheap and fattening food. I have taken courses on Roman history and read extensively into Roman life, as well as the Gladiator diet, and I am entirely sure I know more about the subject than you do. You are also wrong on the account of the Roman diet as well. Only the rich or well off could afford to eat meat frequently and the majority of the population only had the opportunity to eat meat at Religious festivals, where animal sacrifice occurred, or at other big events. Large meals with many different kinds of meat were only common when the rich citizens had banquets and wanted to show off their wealth. Their diet mainly consisted of wheat and wheat based porridge, vegetables, mushrooms, herbs and fruit either grown in the country or imported from various corners of the Empire.
They didn't want to feed them meat because meat was expensive and because barley was an easier, and cheaper, protein option. It's really that simple.
Also, relating to a supposed point made in the blog you provided, the blog poster said: "...perhaps these soils were depleted of zinc over the last 1800 years, but if the soils are low in zinc then the animal that eat these plants are going to be low in zinc also, and the people who eat the animals will also be low in zinc." Or perhaps the people that ate the PLANTS themselves would have had lower zinc, not just the people who ate the animals that ate the plants. That is kind of a ridiculous point to make.