School shootings like the one at Columbine High School in 1999 motivated educators, social workers, sociologists and psychologists to investigate the forces that had driven the shooters to violence. One such investigator was Case Western Reserve psychologist Roy Baumeister, PhD, who suspected that social rejection played an important role, perhaps by triggering negative emotions that were then expressed as aggression.

That hypothesis led him into a series of studies on the psychological effects of social rejection that is providing new insights into the importance of social relationships for self-regulation. "Our initial theory about this was that rejection would cause a great deal of emotional distress," said Baumeister at APA's 2002 Annual Convention in Chicago. "We thought, OK, we're going to reject people in the laboratory, they'll have anxiety and other emotions, and then after that they'll show all sorts of behavioral side effects."

After a number of studies, however, it has become clear that while social rejection does have powerful effects on behavior, those effects are unlikely to be mediated by emotion. "We've gotten all the behavioral effects, but we haven't gotten the emotional part," said Baumeister.

Instead, social rejection seems to undermine self-regulation, making negative behaviors more likely. "Functioning in a social group requires a whole set of inner processes to regulate your behavior," explained Baumeister. "Prosocial behavior--for example, helping others, making sacrifices--often involves doing something that's against your immediate self-interest. Your selfish inclinations have to be held in check. All these sacrifices are compensated to some extent by the benefits of belonging to the group."

Without those benefits, self-regulation can fall apart. "A great deal of psychological functioning is predicated on belonging to the group and enjoying the benefits, both direct and indirect, of that belongingness," said Baumeister. "Social exclusion undermines the basis for these sacrifices--it ceases to be worth it. The whole purpose of controlling yourself, behaving appropriately and making sacrifices is defeated. And so behavior may become impulsive, chaotic, selfish, disorganized and even destructive."

Baumeister's lab has used two basic manipulations to explore social rejection. In the first, a small group of participants is brought together for a brief discussion. At the end of the discussion, the participants are asked to name privately one other participant with whom they would like to continue working. In the social acceptance condition, the researchers then tell participants that all of the other participants have chosen them; in the social rejection condition, they tell them that none have. In the second manipulation, participants are given personality tests and told either that people with their profiles tend to be surrounded by friends as they grow older or that people with their profile tend to become increasingly alone.

Baumeister has found that people who are socially rejected show much higher levels of antisocial and self-defeating behaviors than those who are accepted. A series of experiments, each based on one of the two manipulations described above, has shown that social rejection makes people more aggressive. It also makes them more likely to cheat, less likely to help others, more likely to place risky bets, more likely to procrastinate, less likely to choose healthy behaviors and less able to delay gratification--in other words, less able to self-regulate. People who have been rejected also score more poorly on intelligence tests.

"Social exclusion produces significant changes in behavior towards a variety of maladaptive, pathological, undesirable patterns," concluded Baumeister.