Opposites may attract, but that doesn’t mean they’re a match made in heaven. In fact, recent research has helped explained the phenomenon of doppelganger couples. While participants in a Canadian study were less likely to choose people with similar-looking faces for a short-term relationship, they were more trusting of people with faces that resembled their own — and therefore more likely to end up with them in the long term. The researchers theorize that this response evolved to prevent accidentally becoming sexually attracted to relatives, while at the same time guiding us to fall in love with long-term mates who are reasonably similar to us. “We do not want to date relatives, but we do trust people who are similar to us,” Grossman says.