TG, Grossman is controversial but and he is extensively cited in the aggression literature.
The sheepdog cliche comes from a lot of folks - I don't know the exact origin but it goes along with the 'sheeple' line. Some linguist can track it down.
If you want another really interesting but long read relevant to us - Collins book entitled Violence is a great one.
As Lee mentioned - Skip is an awesome scholar of the issue. Having done the NTI three times - the FOF aspect of ATSA village, team tactics, 360 shoot house, etc. are very useful lessons for the FOGish warrior.
BTW - the last time I did it - there were 3 psychologists and an anthropologist, mixed in with folks like the Marine officer in charge of firearms training.