There is a reptilian brain component that is strong when people are passionate or angry. I wonder if greed falls into this as well? Greed for power, control, and money certainly are the driving forces of Dubya's White House. Here is a google search on reptilian brains. (I'll leave it to you to sort through them--the links on the first page appear all to be commercial or from popular opinion publications in nature, diluting their general credibility without more research).

SRS