Have you ever wondered why old couples look alike so much that they could even be confused for siblings? Well, here’s an answer to that, as provided by scientists.

Trying to understand what could be responsible for this phenomenon, psychologist Robert Zajonc of the University of Michigan conducted his popular ‘Facial Likeness’ study in 1987 and found that couples who have been together for as long as 25 years looked so similar in appearance that participants in the study did not have any trouble pairing them together despite having no prior knowledge of their marriage.

During the study, Zajonc and his team asked volunteers to look carefully at photographs of men and women and match them based on facial similarity. The researchers found out that couples who'd been married for 25 years were rightly paired together a lot.

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An explanation for this, according to Zajonc, is that couples who have been together for that long would have had a lot of shared experiences that left similar lines on faces, and that couples would therefore begin to look more similar. In essence, couples would have had a lot of moments of shared laughter, shared sadness, and would have gone through a lot of emotions together, which leaves the same facial lines on them.

As you grow old together, you tend to adapt yourself and change in accordance with your partner. Your life experiences are reflected in your face. Couples that have shared a happy and joyful life together develop muscles and wrinkles related to smiling and laughter, whereas couples that have been unhappy have frowns, anger and depression reflected in their faces.

On the other hand...

In some other cases, when partners look alike, it could have nothing to do with how long they’ve been together. According to a 2010 report from Personality and Social Psychology Bulletin, people tend to be attracted to members of the opposite sex who look like them or their parents.