First, a twist in the tale: the shape of our jaws and teeth suggest that we were not designed for eating meat.
This is true. If we examine the shape of the jaws and teeth of early humans, there is nothing to tear flesh. We need inch-long canines to tear flesh if we were persistent meat eaters (carnivores). But this does not mean that we did not eat meat. I'd suggest humans first started as vegetarians. There were times in earth's history when the climate was too unbearable; something like a small period of rain, followed by a longer period of draught. This could have forced the species to migrate to new lands in search of food. This could have either lead to two consequences - the species forced to eat their own in order to keep themselves alive, or, the species would have consumed other inferior species (mostly herbivores) after killing it.
Then it became a play of natural selection. Those humans who remained to be only herbivores perished slowly; the others survived. This selection would have driven the species to have a omnivorous diet. But humans were not primarily carnivores. If they were carnivores, we would have in time developed sharper canines. So well, the omnivorous argument could be one reason we don't have canines.
Now I'll be using the above argument and coming to a different conclusion which is more interesting to note...Raw meat takes time to digest. Breaking down the proteins and fat in meat would have taken straight 5-6 hrs of digestion alone. If this was the rate food assimilated in the body, then we would have definitely become undernourished. We have to note the primitiveness of our digestive systems; there were designed for a vegetarian diet.
So consuming meat would have "slowed" the species. They had to take long hours of rest to complete their digestion. This meant they were more susceptible to being prey by other carnivores. They would not have been in a position to flee if they were faced with a threat. This on the one hand could have brought down the population, and this could have resulted into extinction.
But fortunately we were intelligent enough to know how to scare out predators away. On the one hand we did have tools to hunt, and butcher our dinners. They had also provided a means to defend ourselves against threats. On the other had we had fire.
Many historians agree that fire and hunting tools were discovered during a period referred to as the Early Stone Age or the Lower Paleolithic age. I googled to find out how exactly our primitive species looked like around the time. The result - fairly primitive enough.
Their jaws and teeth were similar to ours - they had no sharp and long canines. So what did happen eventually.
They say meat eating has impacted our evolution. But this would have not made sense if we disregard the discovery of being able to tame fire. Fire lead to another discovery - cooking. Cooking processed the food we consumed. Now what actually took 5-6 hrs to digest hardly took an hour or two. We were sufficiently nourished. We had the energy to hunt more, etc. And we were top performers at what we did. This fostered a small change in us. You could say it was the breeding ground for a much more powerful version of ourselves.
The most notable evolutionary change the discovery of fire and cooking brought in was an increase in brain mass. Our brains evolved tremendously. This is partially because of the meaty diet we grew fond of. Now since we had cooked food, we only needed a small time to chew. Hence we didn't need extraordinary canines to chew our food. Plus, we started to consume more meat (proteins), and this lead to many startling changes in the entire body. Here is a small contrast of the times:
Initially primitive humans spent most of their time sitting idle and chewing their food. Now they were sitting idle and perfecting their tools.
Anthropologists would interpret this and remark this was something that indeed revolutionized the human species.
Really there is no meaningful purpose in sitting and perfecting our tools, when they are actually good at whatever their purpose was. But now they actually put their thought into it, and perfected their tools with a view to improve their hunting capabilities. Though they did not actually realize the ballistics of a sharper spear at the time, they observed that sharpers spears were more accurate and effective tools for securing their baits. And tools and hunting were not only the stuff they invested their thought processes in; they actually thought of many other things - constructing sheds so that they avoided rain and the sun, polishing stones to make them sparkle, etc.
We started using our brains. We started becoming creative at what we were already doing.
The increase in brain mass suggests that there were several inter-neural connections within the brain which never existed before. Even at present we are trying to learn more about that. Because it is probably after this we started "settling", forming societies, etc. You'd be truly amazed how far we've come from there...From that small creativity spark to how advanced our civilization has become; truly amazing.
Most of this discourse, was taken from a two-hour documentary from NatGeo. I had seen it a long time ago; when I was in college. I would have rightly titled this post The Story of Fire, but my motive was to make you understand that we owe a part of ourselves to being the meat eaters we once were. We would have been different if we were vegetarians. So I don't think a vegetarian lifestyle is the only one to adopt. Of course it has its advantages. But I don't know what vegetarian life style alone would have resulted our species to become. We have gone through a phase of being meat eaters. We could evolve better in future if we maintained that status. But I don't suggest you have to take a complete carnivorous diet. A balanced diet would do fine.
And what is a balanced diet? I mean you'd have to go to a nutritionist and tell him/her that these are the things I do everyday. He/she would, ideally, do the math, and tell you how many calories you need, and how you can achieve it. So I hope you get the idea of a balanced diet.
So happy eating, and healty living...
PS: there is an enclosure link pointing to a national geographic news article about the same subject. Not that insightful though, but I guess you'd find more if you dig the site further...