Several studies provide evidence that laboratory rats respond to another rat in distress. Two experiments were conducted to determine why. Two general classes of motivation were considered: social and nonsocial. Social-motivation explanations suggest that rats respond because they are concerned about reducing the other rat's distress. This would seem to imply at least the rudiments of altruism. Nonsocial explanations suggest that the response to another rat's distress is not different from the response to one or more inanimate stimuli. Results of the two experiments provided evidence for two nonsocial explanations, sensitization and conditioning. They provided no clear evidence for either innate or acquired social concern. These results suggest that when laboratory rats help a distressed companion, it is not because of altruistic concern for the other; their concern is for themselves.
Available at: http://works.bepress.com/joseph_lucke/7/