How does the book Expression of People and Animals describe human faces?

Psychologists believe that the face is a mirror of human psychology. Napoleon once said, "People are responsible for their faces after 40 years old." This statement is scientific to some extent. The influence of people's psychological state on appearance is realized through the activity of facial muscles. In the history of human development, expression initially had adaptive significance.

Darwin pointed out in the book Expression of Man and Animals that the expressions and gestures of modern human beings are the remains of the expressions and actions of human ancestors. These expressions are useful at first, such as gnashing one's teeth when angry and opening one's nostrils. These are the adaptive actions of human ancestors in fighting wild animals. After years of use, these expressions have been handed down. Other expressions are also traces left by human labor and life from ancient times to the present. Although it is not easy to detect, it exists objectively and cannot be changed.