If something can take hours debating at the forums, videos and blog comments, is the question of whether we were vegetarians from the beginning of humanity or whether we become vegetarians much later, as Paleo's fans often saying.
And with the word "fan" I do not want to sound ironic and I'll give you an example. The founder of the Paleo movement, Loren Cordain , in his book "The Paleo Diet: Lose Weight and Get Healthy by Eating the Foods You Were Designed to Eat" [Amazon], and specifically on page 28 he writes :
The clogging of arteries that eventually results in fatal heart attacks comes about through a process called atherosclerosis, in which plaque (cholesterol and calcium) builds up in the arteries that supply the heart itself with blood.[…]
So, do dietary saturated fats from fatty meats cause the artery-clogging process known as atherosclerosis? If we look at the evolutionary evidence, the answer is a resounding yes.[…]
So, now we have the facts we need to come to closure with the saturated fat-heart disease issue.
Dietary saturated fats from excessive consumption of processed fatty meats and feedlot-produced meats increase our blood cholesterol concentrations, but unless our immune systems are chronically inflamed, atherosclerosis likely will not kill us from either heart attacks or strokes.
However, he promotes a diet high in meat, based on the fact that the Eskimos consume large quantities of meat and they don't die from cardiac problems, regardless of his own notes that, according to research, excessive consumption of meat is causing serious health problems.
Paleo's logic is not wrong, meaning the avoidance of processed foods and the consumption of fresh products is the best choice, but Paleo promotes high meat consumption, with 55% of the daily calories coming from it , which is not the best choice [4, 5, 6, 7].
So the question is if our ancestors were really meat-eaters, as the Paleo movement says or they were vegetarians. Certainly previous generations ate meat but not always because of the lack of money. Meat was something "sacred" and eaten in special occasions, such as Easter or Christmas. That's why in old movies, the people with extra pounds were usually the rich ones.
However, what makes a special impression is that, the Neanderthals who were living in the region of Spain did not eat any meat but consumed fruit, moss, tree bark and mushrooms, doing, as the researchers say, the true Paleo diet.
What the researchers saying is that the Neanderthals were adapting to their situations and their environment, so the nutritional differences between them were probably due to the environment itself. Surely in the next years, Neanderthal's DNA will provide more information on this issue.
But the vegetarians VS meat-eaters issue concerns and another culture as well. According to another study , the ancient Egyptians were also vegetarians.
Scientists examined mummies from 3500 BC to 600 AD and discovered that, like most Europeans, ancient Egyptians were mainly vegetarians, and even though they lived near the Nile River, they consumed almost no fish .
This shows us that our ancestors were nearly all vegetarians . Certainly the need for survival made them change their diet frequently and adapt to the environment they were in. The lack of fruit and vegetables may caused them to start eating meat, and vice versa. Surely the next studies will give more answers about this.
Closing, I want to write about Eskimos' diet and that the traditional Eskimos have lived free of heart disease, cancer, and most other chronic diseases affecting western civilizations these days, maybe are just rumors . A thorough review of the evidence concludes that "Eskimos have a similar prevalence of CAD (coronary artery disease) as non-Eskimo populations, they have excessive mortality due to cerebrovascular strokes, their overall mortality is twice as high as that of non-Eskimo populations, and their life expectancy is approximately 10 years shorter than the Danish population." 
Also, Alaskan Eskimos who are older than the age of 40 have been found to have a 10% to 15% greater deficit in bone mineral density compared to Caucasians in the US . Keep that in mind when you are ready to start any fad diet.