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We all know that every time a man gives us the once-over, he's probably thinking about sex. But now, science can explain why men are constantly checking us out. Turns out, there's a specific formula for their once-over. Some of it's silly, but most of it you can easily nail.

According to Business Insider, every time a men checks out a woman, he's performing a reproductive fitness assessment. Men were designed to look for key features in women. These features make women attractive because they are associated with good health and fertility. When men notice these features, they are subconsciously thinking, she could have my babies! Making them subconsciously, or very consciously, attracted to you.

Science has proven men to be attracted to women with these 6 features. According to the data, here's what it takes to be "attractive:"

A Wider Waist to Hips Ratio. A ratio of 7:10 is particularly pleasing, apparently. The waist and hips are related to childbirth, making men think, those big hips would be great for delivering my baby!

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A High Voice. According to a study cited in the video, a high-pitched voice evokes youthfulness and signifies a small, feminine body, both of which are attractive to men. Let's just say our high-pitched shrieks at the scandalous happenings on the Real Housewives is a sign of evolution at work.

Healthy Hair. Shiny, full, and long hair is very attractive. Again, it's a sign of health and fertility. And thankfully, very fake-able with regular salon visits and blowouts. Remember, it's for the future of the human race.

Smiles. Well obviously, happy people are attractive people. But science has also proven the whiter the teeth, the better.

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Less Makeup. You may think that contouring, layers of eye shadow, and bold lips are making you more beautiful, but it turns out, the natural look is more appealing to men. The video says that men prefer women who use up to 40% fewer cosmetics. But it shouldn't take science to tell you that the natural you, is the best you.

Wearing Red. There's a reason red is associated with lust. Scientists have proven that wearing red enhances attraction. In fact, they've found this phenomenon to hold true in other animals as well. Note to self: dry clean red dress for Saturday date night.

Dark Strands. Gentlemen don't, it turns out, prefer blondes, according to a 2008 survey of 130 men (and 112 women) published in the Scandinavian Journal of Psychology. "Contrary to expectations … brunettes were rated more positively than blondes," the researchers write. Hair length, on the other hand, "had only a weak effect on ratings of attractiveness."

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Height. One (incredibly thorough) 2010 analysis conducted by experts at The University of New South Wales in Sydney — titled "Much More Than a Ratio: Multivariate Selection on Female Bodies" — showed that although factors such as waist-to-hip ratio and bust size affect how men perceive women, they don't tell the whole story. Taller women were rated as more attractive, but — at least evolutionarily speaking — men aren't necessarily after willowy, runway-ready figures. The men surveyed preferred women with legs that were proportionate in length to their height.

Arm Length. Long legs weren't shown to be a feature men seek out, but long arms were. "Scanned bodies of taller women who had longer arms were strongly preferred," the Sydney-based researchers write. Upper arm girth played a role too — apparently men are attracted to women with long and slender arms.

Big Boobs. Hope you're sitting down: Believe it or not, men like big boobs. But especially in combination with a narrow waist, which, the researchers note, several previous studies had already established. In more news that will surprise no one, studies that tracked eye movement showed that when looking at images of women, men first checked out their breasts and waists. "Men also looked for longer at breasts, but attractiveness scores were more likely to be based on waist scores alone than the breast scores," they write.

Overall Grooming. In a 1997 study published in the journal Current Psychology, changeable features like how people groom themselves and posture were shown to be just as important as fixed features like height. The reason: Evidence of self-care signals to others that you're healthy and strong (and thus, a good reproductive partner).

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This all said, there's plenty of counter research that men are just happy to be getting laid at all. One thing's for sure – they're lucky to have us, just the way we are.

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Headshot of Jessica Leigh Mattern
Jessica Leigh Mattern
Web Editor
Jessica Leigh Mattern is a web editor and writer who covers home, holiday, DIY, crafts, travel, and more lifestyle topics. Prior to working for Country Living, she wrote for several lifestyle and women’s magazines including Woman’s Day, Cosmopolitan, and Redbook