Studies have shown that about 2 million years ago, humans began to use stone tools to process food, such as cutting meat and smashing plants  At the same time, humans gradually evolved to form smaller teeth and face shapes, as well as weaker chewing muscles and biting power  Therefore
Research on primates that are closer to humans found that they spend half of the day chewing, their oral muscles are very developed, and their faces are also larger.
 Researchers speculate that the use of tools weakens the power of chewing, which leads to changes in the shape of human faces