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
After using stone tools to process food, more and more food has undergone a higher degree of processing and become easier to chew.
 Researchers speculate that the use of tools weakens the power of chewing, which leads to changes in the shape of human faces