Describe what is physiognomy and how does it relate to 'why they do what they do " regarding the criminal piece?

Physiognomy is the study of physical characteristics of the person in order to determine it's life style and personality. It was considered as a legitimate and respected science during the 18th and 19th century. In this period study of the faces could be related to the criminal look was proposed. This relation was used for the identification of criminals perhaps even before they have committed the crime.