You're in a fancy restaurant when you look across the table and suddenly wonder: Are you on a date or are you looking in a mirror?

If you're with your long-term significant other, it may be both. Research suggests that partners who've been together for many years start to resemble each other.

In defining the rules of the mating game, psychologists and sociologists have long debated whether people seek out romantic partners with similar features to their own or whether opposites do indeed attract.

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And while a recent study suggests that we might not be attracted to people we look like, there may be some truth to the theory that we start to look like the people we’re attracted to.

Or more precisely, we start to look like the people with whom we spend a lot of time. Researchers at the University of MIchigan have found that couples who’ve lived together for 25 years show an increase in similarity of facial features.

Furthermore, the study, which was conducted by comparing photographs of couples when they were first married and 25 years later, saw a greater degree of similarity in couples reporting marital happiness.

What explains this phenomenon? Is it just a matter of perception or is there a genuine physical change that takes place? One argument for the existence of a real physical change is based on the theory of emotional efference, which claims that emotional processes — such as happiness or sadness —- produce changes in the vascular system that are, in part, regulated by facial musculature.

The facial muscles are thought to act as ligatures on veins and arteries, and in doing so, either divert blood from or to the brain. This means that the habitual use of facial musculature — muscles repeatedly acting on the veins and arteries in the same way over a number of years — may permanently affect the physical features of the face.

Thus it follows that two people who live with each other for a long period of time and who are likely to be affected emotionally by common events, such as buying a house or the birth of child, would share similar feelings and be prone to mimic each others’ emotions. According to the theory of emotional efference, this would, in turn, lead to an increase in physical similarity of their facial features.

So whether opposites attract or not, it appears that when it comes to long-term relationships, you may find yourself seeing double.

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