Maroney describes a neuroscientific fear-extinction study as preliminary evidence supporting the notion that out-group hostilities might be influenced by biological predispositions. In the fear-extinction study, subjects were conditioned to fear the presentation of black or white faces with the introduction of an electric shock when such faces appeared on a screen. Then the experimenters stopped using the shock when that race's faces appeared on the screen. Subjects' fear was extinguished much more effectively when the subject was conditioned to fear faces of individuals of her own race than when the subject was conditioned to fear faces of individuals of another race.
Terry A. Maroney,
Unlearning Fear Out-Group Others,
72 Law and Contemporary Problems
Available at: http://scholarship.law.duke.edu/lcp/vol72/iss2/8