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Why Do Women's Periods Usually Happen At The Same Time?

We're just so in tune with each other.
PHOTO: Getty

If you've ever lived in a house full of women, you'll be aware of the hormonal chaos that can erupt once a month. Because as if one period wasn't bad enough, we girls tend to sync up, meaning there are a lot of #feels happening at the same time.

But why does it happen? It's not like we sync up with anything else. Like if one of your housemates' hair is going through an enviable growing spurt, she'll be admiring her brilliant new length while you're still tugging away at your split ends urging them to get a move on.

While it's great to have your friends literally feeling your pain both physically and emotionally at that time of the month, it is still a weird thing for our bodies to do. And it's not in our imagination or some kind of urban myth, either.

A scientific study dating back to 1971—which analyzed 8 continuous cycles of 135 American women all living in a dormitory together—discovered that there was an increasing likeness in the girls' menstrual cycles. So why is that?

It's all to do with "socially mediated synchrony," apparently, which applies to groups of women both of human and animal species. Its purpose, according to the Sydney Morning Herald, is that groups of females become sexually receptive all together, meaning they won't be singled out and therefore targeted by men.

So in the animal kingdom, for example, it prevents the dominant male from taking control of a women simply because of the timing of their "sexual receptiveness." Basically, it's a protective feature put in plays by Mother Nature to make sure we don't get treated as objects by the opposite sex just because we're the only one on our period. 

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That, and it means there's always enough ice cream to go around. Cheers, love. 

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This article originally appeared on Cosmopolitan.co.uk. Minor edits have been made by the Cosmo.ph editors.