Some people like to think there's something fated about who we fall in love with. It's that perfect mix of attraction, compatibility, and of course timing. But in some cases, fate may be taking its cues from birth control pills. First, let's go over a woman's cycle and how that affects attraction. When women are ovulating, their features change in ways that men unconsciously pick up. So men are particularly attracted to women when they're fertile. And it works the other way, too. When a woman is fertile, she's more attracted to men with more traditionally masculine features and who are genetically dissimilar to her, or more compatible in terms of procreating. Of course oral contraception changes a woman's hormonal cycles. Her body thinks it's pregnant and doesn't go through ovulation-induced changes. And in a study published this month in the journal Trends in Ecology and Evolution, researchers say that women on the pill do not show the ovulation-induced attraction to genetically dissimilar partners. So they might be choosing men who are more genetically similar—which could lead to some of the problems with conception that have become increasingly common. Because attraction isn't fate. It's chemistry.