There are significant amount of proof that early humans relied more on plants then meat. Because early men found that it was far more easier to gather than hunt for their food, they mainly focused for their diet, on plants.
I have often encountered the misconception of people needing a high protein level to function. However, the body only needs about 50 to 63 grams of protein a day to function. One ounce of a quarter house steak ( which is about 4 oz total) has enough protein to provide nearly over half of the needed protein! So a whole quarter house steak provides almost double the amount of protein the body needs! Spinach on the other hand, (one ounce) is 15 grams of protein. If one eats a variety of vegetables and fruits and nuts and seeds, they can meet the required amount of protein easily. I should know, I am a long distance runner! I have been constantly told that I need to eat meat to function as a runner. But I still have been able to run the same amount to miles as my cross country team with all the energy and speed I need.
Source from “China Study”.