Women always seem to find the bad boy sexy. The rebellious rogues. Oh how they so darn attractive. But its never been clear why women tend to turn that attraction into long term relationships. That is until now, since there's some science to find out why this is so.

New research reveals that the secret lies in the hormones. A woman might choose to mate with an attractive male because evolutionary it means more attractive kids. But that doesn't paint the whole picture. Research conducted at the University of Texas at San Antonio and published in the Journal of Personality and Social Psychology suggests that during ovulation hormones affect judgment of parenting potential. Kristina Durante, one of the researchers, explains to Live Science:
When women are ovulating, they are more likely to believe that rogues would make better potential fathers, which is why they prefer to pick sexier men over the obviously more dependable men.

Female participants were asked to view online dating profiles of either sexy or reliable men during periods of both high and low fertility, and they were asked to predict the likely paternal contribution from the prospective partners close to ovulation. The result? The women thought the sexy men would contribute the most thinking they'd make better dads in the long run.

In conclusion, to crudely put, if a woman starts dating an asshole, she will be at least once a month be under the impression that he'll make a good long term mate. Durante explains:
So if you want to get the girl, its all about timing. Of course, we're not certified pick up artists so we won't know how to tell you how to ask a woman whether or not she's ovulating. Don't go asking that. You'll just get them weird eyes staring at you. [Journal of Personality and Social Psychology via Live Science]