Pit bulls were bred for hundreds of years for aggression towards other dogs and docility towards humans. Check out "Monser Myths" from a local Pit BUll rescue, BAD RAP.

Also, http://www.atts.org/ is worth taking a look at....temperament testing done on lots of breeds of dogs...the Pit Bull is one of the high scoring breeds on this test. 83.3% of them passed, as opposed to 65.6% of Scottish terriers, 64.8% of Schnauzers, etc.