In his excellent book On Killing Dave Grossman outlines a more complex version of fight or flight based on his observations and experiences in combat. He suggests that rather than fight or flight, we should speak of Fight, flight, posture or submit when talking about intraspecies conflict. The basic idea of his book is that people are very reluctant to kill each other even when ordered to and placed in life threatening situations. He gives numerous examples of soldiers who did not Fight or Flee, but, rather, chose to submit to the enemy, or to posture (that is try to scare the enemy without harming him.)