12 Fantastic Scientific Facts About Friendship

Tina Fey and Amy Poehler are so close they're practically "sisters." Jennifer Aniston and Courtney Cox have been BFFs since their time on Friends. And what would the world be without Harry Potter, Hermione, and Ron watching each other's backs?

Friends are indispensible. And we're not just saying that to make you smile (like your bestie would.) Here, 10 science-based facts that we all need a pal we can lean on — and why.

1. You choose your friends and they choose you. You can't be forced to become close with someone. (A lesson you probably remember from when you were a kid.) 

2. We need allies. Scientists aren't totally sure why we have friends. One theory, though, is that we're unconsciously buidling a support system in preparation of future conflicts. (Be it the need for a tampon right before yoga class or a major earthquake hitting.)

3. Friends cross paths regularly. Scientists have found that we're more likely to become friends with people we see frequently. Think: someone who lives on your block vs. someone who's seven streets over.

4. Every true friendship has certain prereqs. There are five "musts": First, it has to be voluntary. (See #1.) It also has to be affectionate. You and your friend need to be on equal footing and actually LIKE each other. And there also needs to be a mutual sense of give and take.

5. Our best friends are most like us. We're not talking hair color or that you both live in your Frye boots. You and your bestie both share a "social identity" —  that is, how you view yourself and hope the world does as well.

6. Women prefer prudish friends. A Cornell University study found that women tend to snub other females they find sexually promiscuous. (Which is the scientific term for "slutiness.") The reason? We instinctively fear that they're a threat to our own romantic relationship.

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7. Quality, not quantity, counts. It doesn't matter how many "friends" you have on Snapchat — OR in real life. It's way more important how you feel about those friendships. Being happy in them means that you're probs more happy with your life overall. (Interestingly, that's especially true for lesbian and bisexual women.)

8. Giving is more important than receiving. You'd think we'd like friends more when they do stuff for us, but just the opposite is true. Research shows that we cherish doing favors for friends be it cooking them dinner or giving their car a jump-start. The reason has to do with us affirming to ourselves that we're doing something nice because this PERSON is really nice.

9. Having friends has serious health benefits. Seriously. Having a posse of friends reduces stress and depression and boosts immunity. You're less likely to have memory problems as you grow older, and you'll probably also LIVE longer. More time to spend with your friends!

10. Women rely on friends to get through tough times. You know how our bodies have a "fight or flight" switch that's triggered by a potential threat? Well, women are wired slightly differently than men. In times of stress, we "tend and gather." Tend, as in tend to our families, and gather, as in gathering our friends around us for support.

11. Your friends influence your weight. If your BF eats a healthy diet, you are FIVE times as likely to do the same. Friends don't let friends eat crap, in other words.

12. Pals also influence your job performance. Don't have a close bud at work? Then you only have a 1 in 12 chance of enjoying what you do on the job. But having a best friend at work changes everything — you're seven times more likely to get in the flow and be productive. We're pretty sure that phenomenon also translates to PTA meetings.

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