Three reasons why couples look alike

You’ve probably noticed a connection between how many years a couple has been together and how much they look like each other. Any couple has many things in common, and some even have similar facial features. But there are couples who look as if they are brother and sister.

Science has declared that, indeed, the longer you're with a partner (and iam talking seriously long-term here; decades, not months), the more you resemble each other. It's called convergence of appearance.

So what on earth is going on here? Why would people start to morph slowly into their partners? And why are scientists telling us it's actually a good sign?

1. You Look Like Each Other To Begin With.

One of the greatest secrets of the dating pool is that people seem to actively attempt to date people similar to them in some way — in education level, height, age, face shape, whatever. It is called assortative mating, It's not hard to understand why — you like somebody who knows what you're talking about but on a certain level, similarity is also determined in terms of genetics. And that includes faces. A study from 2014 shows that white people in particular pick lifetime mates  who have similar DNA.    

2. You're Sharing The Same Experiences.

The facial likeness study from the now-late psychologist Robert Zajonc of the University of Michigan in 1987 is still the benchmark for people who worry that they're developing their partner's scowl. Zajonc and his team asked volunteers to match photographs of men and women based on their facial similarity, and found that couples who'd been married for 25 years were overwhelmingly paired together.

There are two main hypotheses for why this happened. 

Zajonc thought it was because a long life together meant shared experiences that left similar lines on faces and that couples would therefore begin to look more similar. Others were more practical, believing that it's simply a matter of genetic similarity becoming more evident as the rigors of age remove distinguishing features. Either way, Zajonc's ideas are pretty easy to understand; two people who have lived lives of hardship and difficulty will probably wear similar frown lines.

3. The Happier You Are, The More Alike You Look.

Zajonc's theory of emotional face-mirroring was based on a basic principle: We imitate the people we're around the most. This phenomenon, called unconscious mimicry has been known for ages, and it's why we unconsciously take on the intonation of our friends' voices. It's meant to bond us and make us feel part of a group, but Zajonc also thought it meant that we mimic a spouse over a long period of time, which would gradually reshape the face.