Women are so mean. I'm the new girl at work, having started my job two weeks ago. Yesterday, I had a date after work, so I wore my date outfit to the office. It wasn't scandalous, but it was a little sexier than my usual workwear. I was in a bathroom stall, and I overheard two female co-workers talking about me: mean, nasty, catty talk. And really, my outfit was not terribly revealing. Why are women so awful to one another?

--Upset

Imagine if there'd been three women in the Garden of Eden -- one wearing a fig leaf a little on the small side and two to ostracize her for flirting with the snake.

Welcome to Putdownapalooza! This sort of catty little gossip fest is a female specialty -- an underhanded form of aggression against women who dare to commandeer male eyeballs.

For women, competition for mates is a beauty contest. (Sorry, but Miss Congeniality doesn't cut it.) While it's good to be a good-looking man, for men, appearance just doesn't matter as much as it does for women. Because women get pregnant and left with mouths to feed, women evolved to prioritize finding a "provider" -- a man who's willing and able to commit resources -- over landing some Mr. Adonis. Men know this, having co-evolved with women. They're more likely to dis each other and also trash each other to the ladies over how much money they make than, say, how tight their pants are.

In short, if you're an ugly millionaire, it's best if you're a man. However, if you're a hot barista or pizza delivery person, you'll still get plenty of dates -- if you're a woman. Because men evolved to prioritize physical appearance in mates, women will band together to punish other women for wearing skimpy, revealing clothes or just for being physically attractive. Women seem to recognize that other women do this. Research by social psychologist Jaimie Arona Krems suggests that women tend to dress defensively -- wear less revealing clothes and dampen their attractiveness -- when they'll be around other women that they aren't already friends with.

Prior research (by psychologist Joyce Benenson, among others) finds that girls and women tend to be vicious to newcomers in a way boys and men are not. For women, there generally seem to be "costs from incorporating a female newcomer," Krems explained to me. The women we already know -- "even those we can have some conflict with -- may be less competitive with us. At times, their gains can be our gains. And very often, female friends protect one another" -- sometimes from other women's aggression. "In fact, we might even dress a little more revealingly ... when we're with our female friends than when we're heading out alone ... perhaps because our friends have our backs."

As for you, knowing this, when you're going to be around women you aren't yet friends with, you might want to take it down a notch in sexy or wait till you're leaving work to slinky it up. Remember, as Michelle Obama said, "There is no limit to what we, as women, can accomplish" -- for example, hacking into the new office hottie's LinkedIn and promoting her to "Vice President of Lap Dances."

For pages and pages of "science-help" from me, buy my latest book, "Unf*ckology: A Field Guide to Living with Guts and Confidence." It lays out the PROCESS of transforming to live w/confidence.