WASHINGTON (AFP) - People with a certain gene trait are known to be more kind and caring than people without it, and strangers can quickly tell the difference, according to United States research published on Monday. The variation is linked to the body's receptor gene of oxytocin, sometimes called the 'love hormone' because it often manifests during sex and promotes bonding, empathy and other social behaviors. Scientists at Oregon State University devised an experiment in which 23 couples, whose genotypes were known to researchers but not observers, were filmed. One member of the couple was asked to tell the other about a time of suffering in his or her life. Observers were asked to watch the listener for 20 seconds, with the sound turned off.