When we think of aggression, we typically associate it with males. I picture in my head guys exhibiting physical violence against other guys. For the most part, this is true if it pertains to physical aggression. Researchers believe that males tend to display physical aggressiveness more than females because males have higher levels of the hormone testosterone. However, the correlation between testosterone and aggression is quite controversial because aggression may cause higher testosterone rather than the other way around. Regardless, research has shown that testosterone has a positive correlation with aggression.
Despite the popular belief that males are more aggressive than females, it has been discovered that girls tend to be higher than boys in relational aggression. Relational aggression is a form of indirect aggression that's displayed by acts of gossiping, social exclusion, and nonverbal putdowns. Girls tend to show their aggression through actions that "stab others in the back." One of the possible reasons for this is because of the cultural acceptance of aggression. Girls receive more negative feedback for physical aggression during their developmental years. This makes indirect aggression more socially acceptable for girls. More information regarding gender differences in aggression can be found here.
I thought it was interesting that the gossipy behavior that girls tend to use is a form of aggression. I suppose in a way that it's their way of displaying their anger and getting back at others rather than fighting physically. Additionally, girls tend to be weaker than guys so they're not as capable of using physical force. I still wonder what factual evidence there is that supports the stance that girls have higher relational aggression. Is it more observational? Nevertheless, it appears that males tend to display physical aggression more and females tend to display relational aggression more.