The two of them looked almost exactly alike: same skin tone, similar hair and beard, same height and body shape, similar age, similar glasses, wearing similar suits.

It was as if my pal was marrying himself.

Most couples do not look that much alike. But they do tend to look alike.

How about you and your partner? I bet you look similar in age. There is hell to pay socially if one partner looks much older than the other. Ask rich men who marry much younger women.

Does your skin colour match that of your partner? Opportunities and prejudices push us in that direction, perhaps less now than in the past.

Do you both wear glasses or not? Age plays a role here; so does amount of reading and preferences for appearance.

Similarity in physical attractiveness is common. In this regard, birds of a feather flock together.

I remember seeing photos of a PhD student and her husband. They had the same dazzling smile and the same level of attractiveness, and they sat in matching reclining chairs in their lounge room.

A recent study found that spouses tend to have more similar genes than do people in general. That could be because we tend to couple with people who live near us. We may share ancestors going back farther than anyone has records for.

We tend to partner with someone who is similar to us in various ways. That similarity can extend to likes and dislikes, education level, religious and political orientations - and appearance.

Scientists call the propensity to couple with a similar person assortive mating. The reason for this effect is not clear, but it may have to do with our knowing and liking ourselves. We may project our self-perceived positive qualities on to others who seem similar to us in some respects.

Couples may look alike because they unconsciously copy each other's facial expressions and mannerisms. We may also copy clothing and hair styles from our partner. This effect is more obvious with same-sex partners. Observational learning over many years can have powerful effects.

Although people tend to couple with others who are similar to them in appearance, there are exceptions. If you are in the exception group, you might wonder why. Chance? Or something more interesting about you, your partner, or your life?