There's a strange reason why most couples look alike.

We often face the fact that many married couples look more like brothers and sisters than partners between them. And we assume it's because they've spent so much time together, they take each other's shadow. Even when they start to dress alike and take each other's vices, we think that's also very nice. But when are their characteristics so similar that they look like twins?

Thanks to a medical study, we know the reason for this dilemma. And the answer is: Because married couples may have similar genes. Yeah, exactly.

Researchers at universities in Pennsylvania, California, and Boston have found that people are more likely to marry someone of the same origin. Before today, free travel and online flirting, people had no real choice but to contact (and reproduce) people within their local community.

Published in PLOS Genetics, the study found the pattern of white couples marrying and having children inside them as a recurring custom with time. Evidently, people of Jewish background from northern and southern Europe were more likely to marry someone of the same genetic background as themselves. Fortunately, they studied families over three generations and found that this tendency to mate with someone sharing the same background is in decline over time.