Why are some women "catty"? What is their motivation?

Some women seem to really delight in making passive-aggressive attacks on other people (usually women), trying to make the other feel bad about themselves in some way. I’ve also noticed the catty women seem to target attractive women the most. Why is this behavior so common? What motivates this person to make others feel worse? Best theory I have is it is somehow a competition to solidly entrench oneself as being perceived as the prettiest and most popular within . This sounds like a high school problem, but it is just as prevalent in adulthood. Less attacks maybe, but with sharper claws.