EarlyHomoevolved bigger encephalon and larger bodies than our more ancient ancestors , yet member of our genus also had smaller jaws and a weaker pungency force . According to a newNaturestudy , using canonical stone tools to slice up raw marrow allowed ourHomoancestors to build up smaller features colligate to chewing . These curt faces and smaller jaw may have led to further changes , such as ameliorate speech .
By about 2 million years ago , Homo erectuswere feature big brains and big body that , along with larger forage ranges , increase their daily energetic requirements . But in addition to their smaller , more characteristically human facial features , they also had humble catgut . This seemingly self-contradictory combination of increased energy demand with decreased chewing and digestive capacitance may have been made possible by introducing more refined meat into the dieting – but cooking was n’t common until just 500,000 yr ago .
To consider the chewing performance of modern - day humans , Harvard ’s Katherine Zink and Daniel Lieberman fed dozens of adult guinea pig goat meat and starch - plenteous underground storage organ like gem yams , carrots , and red beetroots . They measured the mesomorphic effort require for chewing by using pawn attached to the jaw , and they also examined how well the food for thought was broken up before it was swallowed . " What Katie did was creative but sometimes , frankly , a little stomach - churn , " Lieberman says in astatement . " Not only did she have people come into the lab , masticate raw meat and other foods , and spit them out , but then she had to analyze the stuff . "
By consuming a diet that ’s one - third meat , and by using stone tools to slice up rude meat and pound plant stuff before eat , earlyHomowould have need to masticate food 17 per centum less often and 26 percent less forcefully . This would have carry through them 2 million chews a year .
" Humans can not consume naked as a jaybird center in effect with their low - tufted tooth . When you give people raw goat , they chew and chew and chew , and most of the butt is still one large clunk – it ’s like chewing gum,“Lieberman adds . " But once you start processing it automatically , even just slicing it , the effects on manducate functioning are spectacular . "
Not to mention , a diet that ’s one - third meat would have enabled earlyHomoto rise their pricy prominent encephalon and enceinte bodies . Unlike most other animals that swallow their food whole , mammals chew their solid food into small pieces that leave digestive enzymes to break in them down efficiently . But most mammal last on comparatively low - calibre diets ( of locoweed , for illustration ) , so they have to chew all twenty-four hour period to extract enough vigor . Even our close congenator , the chimps , spend half their sidereal day chew – and forcefully too .
Over evolutionary time , the littler manduction - bear on bones and muscles of our ancestor may have made it possible for other purpose related to speech production , motive power , thermoregulation , or even changes in the size and shape of the brain .
