Unlike wolves or dogs, human teeth are not made for chewing meat. Human teeth are grinders, not slicers, meaning that meat does not break apart. This is why our closest animal relatives, chimpanzees, spend about half their day chewing. Although cooking helps to tenderize meat, making it easier to chew, evidence of human cook fires only goes back about 500,000 years, and fossil records show that humans were eating meat 2.5 million years ago. So what did humans do before that, since weaker jaws and smaller teeth had already evolved? Simple: they cut it up.
A study published March 9 in the journal Nature addresses the question of why and how our ancient ancestors developed smaller and weaker teeth and jaws just at the time they were starting to eat more meat. Harvard University professor and paleoanthropologist Daniel Lieberman says that it was only possible after those early humans started using tools to cut up their food.
The study used more than a dozen volunteers to eat raw meat and root vegetables while the researchers observed how much chewing was required to ingest it. They found that there was a 17 percent reduction in the number of chews required if the meat was first sliced up and the vegetables pounded. Katherine Zink, a human evolutionary biology researcher also from Harvard, says that comes out to 2.5 million chews per year less than if the food was not pro-processed with stone tools.
Electrodes attached to the test chewers’ faces measured the activity of the four main chewing muscles. In addition, a dime-sized force transducer was placed between the first left molars to measure chewing force. The volunteers were then given samples of raw meat and vegetables to chew. Some were preprocessed by slicing or pounding with a stone tool, some were completely unprocessed, others were roasted.
Raw goat meat was used for the tests since it is the closest to wild game that the researchers could obtain. The participants were asked to chew each sample until they could swallow it, although they were then asked to spit it out so the particle sizes could be measured. The findings showed that the meat that had not had some kind of processing simply could not be consumed, but that even a small amount of slicing let it be broken down enough to swallow.
Results of the chewing experiments led the researchers to conclude that simple mechanical processing would have been necessary for primitive people to include meat in their diets. This ability led evolutionary changes resulting in smaller jaws and teeth.