Nice eyes and a sense of humor are great, but it turns out what will really lock her in for life is how generous you are, according to a new study in Evolutionary Psychology.

Researchers from the University of Worcester in the UK showed more than 200 women pictures of the same two men—one more attractive, one less—in different scenarios. Some portrayed the more handsome guy being altruistic, while others favored the less attractive guy. 

As expected, the physically attractive men were rated higher than the less handsome guys in general, and this was only amplified when they were shown rescuing a kitten from a tree. But it was actually the charitable chaps who were consistently rated as more desirable for long-term relationships—regardless of how good looking they were.

“Possibly most interestingly, we found that if a women could choose only one of these traits for a long term partner, then it would be more likely that he was altruistic than physically attractive,” says study author Daniel Farrelly, Ph.D., senior lecturer in Psychology at the University of Worcester. In their study, ladies opted for a less attractive fellow if he was generous over a hot-but-selfish guy.

Why? Female mate preference has evolved to where women are more choosey in what they look for in a partner who will potentially father their offspring, Farrally explains. “One thing that is important in mate selection are signals that a long-term partner has the necessary psychological characteristics to indicate that he will be a good father, including kindness, generosity, and an altruistic nature,” he adds.

Interestingly, the opposite was actually true for one-night stands—women found giving guys specifically less attractive when considering short-term relationships.

So are you screwed if you don’t volunteer at a soup kitchen? Not so much. You can show her your charitable side with anything where there is clearly a cost involved, Farrally says. You have a few options:
•    Financial philanthropy, like giving a dollar to a homeless guy or adopting an endangered animal in the local zoo.
•    Giving your time, like volunteering or helping out in a local charity shop.
•    Enduring physical costs, like donating blood or bone marrow.
•    Any heroic act (think less throwing yourself in front of a bus and more that rescuing a stranded kitten from up a tree).