When two people live together for a long time and have a good working relationship, they often begin to look alike. This is because they are constantly mirroring each other's facial expressions, which, over time, builds muscle definition in the same areas of the face. Even couples who don't look facially similar can appear similar in a photograph because they use the same smile.

In 2000, psychologist Dr John Gottman of the University of Washington, Seattle, and his colleagues, discovered that marriages are more likely to fail when one partner not only does not mirror the other's expressions of happiness, but instead shows expressions of contempt. Instead, this opposite behaviour affects the smiling partner, even when they are not consciously aware of what is happening.

Craig is a 22-year-old student currently studying psychology at Bournemouth University. He runs a self improvement blog and community filled with useful advice. His main aim is to help people exceed their expectations and reach their true potential. If you enjoyed this post, get free updates via RSS or E-mail.