The introduction of raw meat into the diet and the use of basic stone tools could explain evolutionary changes characteristic of early humans, reports a paper published in Nature. The study suggests that meat and tools, not the later advent of cooking, would have freed early humans to develop smaller chewing related features - such as smaller, shorter faces, and smaller teeth - which may have allowed selection for other functions, such as improved speech or thermoregulation.
By the time of Homo erectus (about two million years ago), humans had evolved bigger brains and bodies that had increased our daily energy requirements, but, paradoxically, also evolved smaller teeth, weaker chewing muscles and bite force, and a smaller gut than earlier human ancestors. It has been suggested that these changes were made possible by incorporating more meat in the diet, by slicing or pounding food using stone tools, or by cooking. However, cooking did not become common until 500,000 years ago.
Daniel Lieberman and Katherine Zink assessed chewing performance by feeding adult subjects standardized samples of meat (goat) and the starch-rich storage organs of plants (jewel yams, carrots and beetroots). They measured the muscular effort required for chewing and how well the food was broken up before swallowing. They find that by eating a diet composed of one-third meat, and slicing the meat and pounding the plant material with stone tools before eating, early Homo would have needed to chew 17% less often and 26% less forcefully.