from waste dumps, fossils and contemporary hunter gatherers we know that the primary food source was the much more reliable plant foods. Except on the rare occasion where people settled a previously uninhabited area with much docile wildlife, a stone age hunter would manage to get big game only quite rarely. Anyone interested in this topic should read Jared Diamond’s Third Chimpanzee for a good account of this lifestyle.
(Regarding) the meat-brain growth hypothesis, this idea has previously been nearly universally thought at schools, however its foundation is actually rather weak since increased meat consumption and our increase in brain size don’t quite match up in time (meat consumption being increased somewhat later). The current best explanation for our high intelligence is given in Chimpanzee Politics by primatologist Frans de Waal. He shows that due to the peculiar social structure of chimps (and our ancestors) compared to gorillas and bonobos, there occurred a near a continuous struggle for dominance in the group. This struggled favored those who could best form alliances, plot, deceive and lie, i.e. it favored intelligence, leading to the intelligence explosion that lead to us.
…In the relatively short periods (compared to our entire existence as a species) of colonizing areas such as Europe, Asia, Australia, the Americas and the Polynesian islands (including Madagascar) people tended to hunt existing fauna intensively. This often led to the total extinction of many species as predation greatly exceeded birthrates for the nonhuman animals. The hypothesis that climate change killed those species… simply wouldn’t explain the timing (people arrive > fauna dies; regardless of prior climatic changes the animals did survive). For the majority of the existence of our species though people predominantly ate plants.