For decades, the theory has been that the emergence of stone tools led early humans (around 2.6 to 3.5 million years ago) to hunt for increasingly larger animals and therefore to eat more meat–and that increase in nutrition led to the increase in human brain size. “Flaked tool use and meat eating became defining characteristics of the Homo genus.”
A newer theory, however, suggests that, instead of hunting and eating meat, early humans used those stone tools to scavenge carcasses left by large predators–to break bones to get at marrow and brain. Bone marrow (fat) may have been more important than the meat (protein) itself; marrow stays fresher longer, is obtained more easily than flesh-meat, does not require as advanced a tool, and is highly nutritious and involved with brain and eye development.
Early humans may have been scavengers rather than hunters …
Read the article (Richard Kemeny, Sapiens, 31 March 2019).
And, go to the source — Origins of the Human Predatory Pattern: The Transition to Large-Animal Exploitation by Early Hominins (Jessica C. Thompson, et al., Current Anthropology, February 2019).