How did the study of human development emerge as a discipline?

Answer 1

people struggled to cure illnesses since ancient times and this prompted them to seek understanding of the human body... as times pass, it developed into various disciplines like anotomy and physiology

Answer 2

Study of any topic sufficiently interesting makes it into a discipline and this field is no exception. After all human beings will naturally be interested to study how they have come this far and where they are headed. It is a multi-disciplinary field drawing upon archaelogy, history, civics, anthropology, science, philosophy etc.