The earliest humans ate a diet similar to that of apes and chimpanzees, consisting mostly of fruit and leaves with occasional insects and meat. As humans developed tool use, meat became a much larger portion of the human diet. Eventually, the development of agriculture helped round out the omnivorous diet.
Around one million years ago, most of the human diet came from gathering and scavenging. Homo erectus used stone tools, however, so occasionally a tribe brought down a large beast to add meat to its diet. By the time of the Neanderthals, around 300,000 years ago, hunting became a primary source of protein for early humans. Those not involved in the hunt would gather fruits, vegetables, roots and nuts to round out their diet.
The major change in human diet occurred around 10,000 years ago with the development of agriculture. Domestication and cultivation of wild grains led to a significant increase in the calories available to humans, increasing the population and removing the need for every group member to spend most of his time acquiring food. This, in turn, led to the establishment of civilization and the growth of human society, paving the way for further technological and scientific development.