Perhaps no question in developmental psychology has created more contro­ versy than that o f whether psychological traits and behaviors are caused by the child's "natural” endowment or whether they are caused by the environmental experiences the child has in the course o f his or her life. Referred to as the nature-nurture controversy, this issue has been as powerfully debated by those concerned with youthful aggression as by other developmental psychologists. In the context o f youth violence, the extreme form o f the nature-nurture con­ troversy boils down to the question o f whether a child’s aggression is caused by the child’s innate biological disposition, or whether it is caused by environmen­ tal factors such as the child’s early experiences, family life, economic conditions, school experiences, and choice o f friends.