Who was one of the first scientists to systematically study emotional expression, including the facial expressions and body language used to express different emotions?

It is Charles Darwin who is the first to systematically study emotional expression. He is known for his theory of evolution in biological science, but he had also made an important contribution in Psychology. Charles Darwin conducted an experiment on emotion, on how people recognize emotion in faces. He argues that all humans and even animals show emotion through similar behaviors. Examples are happiness, sadness, fear, anger, and disgust.