Relational Aggression Overview
Until the 1990s, it was widely assumed that girls were nicer than boys; that they didn’t engage in bullying and domination of their schoolmates. The assumption was wrong.
What researchers found when they focused on the folkways of adolescent girls was a form of aggression that was far more sophisticated, covert and possibly more harmful than the physical oppression of the traditional male schoolyard bully.
Instead of targeting a victim’s physical inferiority or isolation, girl bullies attacked their victims through what girls value most—their friendships and social acceptance. The girl bully’s weapons were exclusion  , gossip, rumor and slander—techniques that kept their assaults well below adult radar. This cruel form of bullying was dubbed relational, social or indirect aggression, and it has proven to be at least as common among preadolescent and adolescent girls as physical bullying is among boys. 
Adding to the invisibility of the Machiavellian girl subculture that practices relational aggression is the nature of the bully. Instead of the openly domineering goon that springs to mind at the word “bully,” the oppressors in the female social system were likely to be among the most attractive, popular and socially prominent girls in the class—the kind teachers and school administrators dote on.
As the study of relational aggression progressed, it was discovered that girls held no patent on it. Boys practiced it as well, although at a less sophisticated and probably less destructive level. Since physical prowess largely defines the childhood and adolescent male social order, physical bullying remains the preferred form among boys.
The female preference for relational aggression is usually attributed to society’s image of the ideal female as a non-aggressive nurturer, and the resulting social stigma that attaches to overtly aggressive behavior by women, who risk negative labels (e.g., bitch, nag or shrew). However, the origins of the preference probably lie far deeper in human evolution. There are several likely components:
In short, indirect aggression may be somewhat hard wired into the female human psyche, and the expectation of overtly nurturing; cooperative female behavior (and the reality of covert female aggression) may date back to our proto-human and even pre-human ancestors.
Another factor in the female preference for social aggression is that it does a very effective job of achieving aggression’s purpose—inflicting pain. Indeed, it produces pain equivalent not only in intensity but also in kind to that of physical injury.
Modern medical imaging techniques have recently demonstrated that the pain of social exclusion arises, in part, from the same brain regions that report physical pain, and, in animal experiments, opioid pain reducers, like morphine, and increased levels of the brain’s own the pain-blocking endorphins, also blunted the pain of social loss. 
The vulnerability of adolescent and preadolescent girls to relational attacks arises from the importance they attach to their friends and other social relationships. The motivation to use those relationships as weapons derives from the same source.
 While excluding other girls from groups or activities is included in almost all descriptions of indirect bullying, an Australian study found that girls did not consider the activity aggressive. The author of the study suggests that it may be perceived as a way of defending their friendship circle from intruders. See Leckie, B, Girls, Bullying Behaviours and Peer Relationships: The Double Edged Sword of Exclusion and Rejection, University of South Australia/Flinders University, 1997, available at www.aare.edu.au/97pap/leckb284.htm, accessed 12/3/2004
 Österman, K., Björkqvist, K., et. al; Cross-cultural evidence of female indirect aggression, in Aggressive Behavior, 24, 1-8, 1998, available at www.vasa.abo.fi/svf/up/indirect.htm., accessed 12/6/2004
 Foregoing components drawn from Campbell, A., Female competition, causes, constraints, content and contexts, in Journal of Sex Research, 2004, available at www.looksmart.com, accessed 12/6/2004
 Panksepp, J, Feeling the Pain of Social Loss, in Science, vol. 302, pp. 237-239. 10 October 2003, available at www.sciencemag.org, accessed 12/6/2004