Surely you remember that fateful day you met the love of your life. What was it that first made you swoon? Was it his sparkling eyes, his sense of humor, or his love of death metal? Despite all the heart-eye emojis in your memory, it probably wasn't any of those things. One of the real secrets of white-hot attraction is something a lot less sexy, according to a recent study published in Nature: It's a part of your genetic coding.
All humans have their own unique human leukocyte antigen (HLA) complex, which helps the immune system differentiate between its own cells and those of unwanted viruses and bacteria. But they also can be hugely influential when it comes to attraction. The researchers studied attraction patterns in 254 couples and found that having a partner with a very different HLA complex "correlates with sexuality and enhances the desire to procreate." That means your genes determine how badly you want to get it on with your partner. So opposites do attract!
It also might account for why you think your significant other smells sooooo good. The researchers saw that most of the couples were more inclined to think fondly of their partners' odors if their HLAs differed. (However, the researchers noted that because predilections for odor were self-reported, it could have been influenced by the fact that they were already smitten and in a relationship.)
All of this is more than just quirky trivia to shout out at a bar. It can actually benefit evolution—at least, in the case of animals. The researchers found that if two animals with unalike major histocompatibility complexes (or MHC)—which is what scientists call all animals' version of HLA—loved each other very much and they mixed their bodily fluids together, then their baby would be born with a super-charged immune system.
Instead of asking "Hey, baby, what's your sign?" next time you're out, try asking "What's your genetic HLA blueprint?"