“Women,” the British writer Anthony Burgess once said, “thrive on novelty and are easy meat for the commerce of fashion. Men prefer old pipes and torn jackets.” That’s not entirely true, of course. I’m a fashion-challenged male myself—and one of those rather rare gay ones to boot—but most men aren’t quite as indifferent about their appearance as Burgess would have us believe. Not today’s men, anyway. As Reuters correspondent Ellen Wulfhorst points out, the latest in menswear has a long history of playing second fiddle to female vogue, but those in the know now see it as a potential sleeping giant, with the wide valley in sales figures between what the two sexes are willing to spend on cosmetics and stylish clothes increasingly narrowing.

Still, if major industry events like last week’s Mercedes-Benz Fashion Week in New York City are any reflection of human psychology, it’s women who seem especially eager to invest their hard-earned dollars in feathering themselves up with designer labels, spending over $100 billion a year to do so. From handbags worth more than a new Hyundai, to stiletto heels that would set you back more than treating Jill Duggar’s whole litter to a feast, to sunglasses that…. well, you get the idea. It’s a decidedly feminine affair, this conspicuous consumption of high-priced fashion goods. And from a scientific perspective, that’s a bit of a puzzle. Here’s why.

The average heterosexual man simply doesn’t care what, or who, women are wearing. Study after study has found that men see a frugally attired woman as being just as sexually attractive as one whose outfit screams fashionista diva. Place her in a fancy pair of Jimmy Choo shoes or no-name heels from Walmart; male arousal just isn’t influenced by such vanity items.

It’s a very different story for women’s perception of male attractiveness, however. Women’s feelings about a man’s desirability are swayed by cues to his wealth. Put the same guy—even the same image of that guy, just photo-shopped accordingly—in an Armani suit, or a Mercedes, or (as Cardiff Metropolitan University psychologist Michael Dunn found in the most recent experiment) a luxury apartment, and women’s subjective evaluations of that man’s attractiveness are significantly higher than if they see him in a pair of boxers, a Toyota Corolla, or a cheap flat. Evolutionary psychologists explain this sex difference through “parental investment theory”: since the physiological risks associated with casual sex were so much higher for women than men in the ancestral past, women evolved to be choosier overall about their reproductive partners, preferring those males who signaled that they had the resources to help raise any shared offspring.

So if women aren’t spending big bucks on fashion and other luxury goods to score a man, why are they doing it? Saying it’s “for themselves” or “because it’s fun” is fine, but from an evolutionary, non-conscious perspective, it means nothing. It turns out that the real reason women flaunt their handbags and couture has to do with the other women around them. The latest Balenciaga bag may send a message that a lady has great taste, but it’s also telling other women around her that she probably has a man who bought it for her (so back off!) or it’s marking her as a formidable contender on the competitive scene of single ladies. At least, that’s what the data from two recent studies tell us.

The first comes from researchers Vladas Griskevicius and Yajin Wang at the University of Minnesota. When asked their impressions of a woman drenched in extravagant garb and dangling with currency incarnate, female participants perceived her as being in a more serious, committed relationship than those less sumptuously attired. This effect pans out regardless of who really paid for those luxury items; other women’s default assumption, for better or worse, is that she must have a male partner who lavishes her with such objects. Griskevicius and Wang also found that when women feel threatened and jealous in the romantic realm—like when some vixen flirts with their husbands—they’re more likely to splurge on designer brands. This broadcasts loud and clear that their partner is taken. In other words, it’s what other women think that matters most in this game of “intrasexual competition”.

The second study, cheekily titled “The Rival Wears Prada,” led by Lisa Hudders of Ghent University, Belgium. Hudders and her team fine-tuned the previous study, investigating the specific types of luxury goods that women use to prevent their men from getting poached. To do this, they recruited about 200 Flemish women to participate in a controlled experiment. Half of the sample (those randomly assigned to the “non-competitive” condition) saw a photo of a pretty landscape and were told to imagine walking through that place while enjoying the scenery. The second group (those in the “competitive” condition) saw a photo of an attractive woman and were told to imagine being at an event where this other woman began flirting with a guy whom they were interested in themselves: an “attractive, smart, funny, intelligent man with an engaging personality.”

After picturing one of these scenes, the participants were asked to read one of three different product descriptions: an advertisement for a mass-produced non-luxury product such as a cheap ballpoint pen; one for a pricey non-appearance-altering luxury item such as the latest smartphone model, or; for an attractiveness-enhancing luxury object, such as a one-of-a-kind designer dress. The women were then simply asked how much they personally wanted that object.

The results confirmed Hudders’s suspicions. Women who’d been primed with the competitive dating scene and who then read about the designer dress desired that item significantly more than did women in the other conditions (even women who read about that same designer dress but who didn’t imagine the other flirtatious woman beforehand). From this, the authors concluded that sexual competition between females spurs them on to purchase luxury goods, but only items that are capable of accentuating their physical beauty in the eyes of desirable men—things like figure-enhancing dresses, expensive face creams, Botox injections—not just expensive things like smartphones.

If this message of “don’t even try to compete with me, darling” is what women hope to communicate to rivals by glamming it up, it seems to work. After all, in a follow-up experiment, Hudders showed that women perceive other women who spend an exorbitant amount of money on luxury products as more attractive, more ambitious, sexier, and of higher status than their peers. They are regarded as intimidating opponents on the reproductive battlefield; therefore, they’re less likely to be challenged.

These data are rich pickings for anyone savvy enough to realize that predictable algorithms of evolved human psychology underlie consumers’ shopping decisions. So listen up, marketing gurus in the fashion business: advertising campaigns that play off women’s “intrasexual competition” (read, female rivalry and jealousy) push all the right buttons in female cognition. With all the theatrics trotted out last week at Lincoln Center for the Fashion Week, a catfight on the catwalk could have gone a long way.

Jesse Bering, an Associate Professor at the Centre for Science Communication at the University of Otago, New Zealand, is the author of Perv (2013), Why Is the Penis Shaped Like That? (2012) and The Belief Instinct (2011). Follow him on Twitter @JesseBering.