Anyone who has ever attended high school will no doubt be familiar with "mean girls", which are usually cliquish girls who behave intentionally mean towards members of their own sex.

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While most of us will eventually outgrow this phase, the need for power and validation can sometimes manifest into controlling, manipulating and denigrating behaviors in adulthood.

But why do we behave this way in the first place? According to one scientific review published in Philosophical Transactions of the Royal Society B, evolution could be the reason why women are so catty and gossipy towards each other:
"...females prefer to use indirect aggression over direct aggression (i.e. verbal and physical aggression) because this form of aggression maximizes the harm inflicted on the victim while minimizing the personal danger involved."

"...females punish other females who seem to make sex too readily available using indirect aggression," by devaluing them in a "concealed way which diminishes the risk of counterattack."
To support this theory, the paper cited an earlier study which revealed how females across several species would rather engage in "indirect aggression" when competing for mates. This was to reduce the chances of being injured or killed, which in turn would leave their offspring more vulnerable:
[T]he benefits of using indirect aggression seem clear — fewer competitors and greater access to preferred mates, which in ancestral times would have been linked to differential reproduction rates, the driving force of evolution by sexual selection.
But it's not just the ladies who do this. As the study author notes, "There is virtually no sex difference in indirect aggression. By the time you get to adulthood, particularly in work situations, men use this too."

[Livescience]