Girls form cliques with like-minded friends and exclude those who don't fit in. Boys take risks, show off, and never back down from a fight. Adults should not be surprised by this behavior. We acted the same way when we were teens. Teens haven't changed much, but the world around them has changed a great deal.
Modern culture is saturated with violence.
Television, movies, and pop music feed teens a steady diet of mayhem, killings, and degradation. With the emergence of video arcades and computer games, kids can take an active role in the killing. More disturbing, kids are repeatedly exposed to real images of violence as well. The evening news is filled with car crashes, suicides, and mass killings. Teens watch kids shoot classmates, and land on the cover of Time magazine.