Compare ancient human with modern human in food habits! We can make this comparison based on availability of a variety of foods and food habits. Ancient humans usually lived on roasted raw meat of animals hunted by them. They also lived on raw plant foods they could search in forests. Modern humans have a great variety of plant and animal foods to eat. This was about food availability in ancient and modern times. If we make food habit-based comparison between ancient and modern humans, we find that ancient human had no specific choice to adopt a habit of eating vegetarian or non-vegetarian foods.
Vegetarian and non-vegetarian
The concepts of vegetarian and non-vegetarian emerged few centuries ago when humans were able to make a choice of their foods. This created a different class of people based on their food habits: vegetarian and non-vegetarians. This trend also caused creation of vegetarian restaurants, a separate category of restaurants that serve foods derived from plant products only, without an animal content. These restaurants became more popular because both vegetarian and non-vegetarian could dine on these places, though latter are served only vegetarian dishes here.
Distinction between a vegan and vegetarian
Some vegetarian people have more diet limitations. For them, definition of animal products is entirely different. For instance, in Jainism, people have prohibition of eating products derived from animals. If you consider this aspect, egg is not an animal but a product derived from animal. Milk is a dairy product but obtained from a cow, an animal. So, a different class of people with strict vegetarian food habits emerged which is more than a vegetarian, or rather call pure vegetarian. Accordingly, a new category of restaurants, called vegan restaurants, also emerged for strictly vegetarian people. The difference between a vegetarian and vegan is quite clear from this discussion. You can understand in what way vegans are distinct from vegetarians.