Just a few years ago, the two superhuman specimens comprising Brangelina decided to join forces in marriage while the rest of us mere mortals looked on in celebration — and envy. Today, however, we've learned that Angelina Jolie has filed for divorce from Brad Pitt. And, somehow, we'll all have to just get on with our lives.Sure, it can seem like certain people are truly made for each other (especially when their "perfect" personas, for better or for worse, take on cultural significance ). But celebrities are people, too. And people in the U.S. have a divorce rate of around 40-50% (and it's even higher after the first marriage). So it's not uncommon for even those seemingly perfect relationships to end for totally unpredictable — yet totally understandable — reasons.Luckily, research has uncovered some very interesting (and helpful) patterns in our pairings. Click through to see a few things science can tell us about the way relationships develop and, ultimately, end.