FACIAL expressions of emotion are innate, not learned, according to new research that compared the facial expressions of sighted and blind athletes as they weathered defeat.

In the first study of its kind, researchers in the US say they have demonstrated that facial expressions conveying emotion are hard-wired into our genes, not learned through observation.

Even the so-called "social smile" — displayed stoically by the silver medallist at the medal ceremony, for example — is instinctive, with sighted and blind athletes using the same facial muscle movements to deliver a forced smile in difficult circumstances.

Using more than 4800 photographs of athletes from 23 countries, the researchers compared the facial expressions of sighted and blind judo athletes who took part in the 2004 summer Olympics and Paralympic Games.