Physiognomy is the theory, now discredited as a science, of relating an individual's character, personality, and temperament to the shape of his or her face, head, and/or body. The ideas behind it go back to Hippocrates, who believed that the physical characteristics of the human body revealed personality traits; Aristotle performed studies on how hair, limbs and facial features predicted personality and temperament. Such theories thrived throughout the Middle Ages and the Renaissance, and by the 18th century, the study of physiognomy was still taken very seriously as a medical topic. Physiognomy is not a true science, as the correlations between a person's physical appearance and their character and/or intelligence are not always accurate. Its association with scientific racism in the 19th century has further sullied physiognomy's reputation.