How kind you are could be affected by a change in a single gene. What's more, others can tell if you have the gene even if you don't speak a single word.
There are several variations of the gene that codes for the receptor for the hormone oxytocin. Aleksandr Kogan at the University of Toronto, Canada, and colleagues wanted to check whether these variations influence behaviour, since high levels of oxytocin are believed to make people more sociable.
Kogan's team asked 116 volunteers to watch 23 silent videos that were 20 seconds long. Each showed a person's response to their partner telling them a story of personal suffering. The volunteers were asked to rate how kind and trustworthy the person in the video appeared to be.
People with the so-called GG version of the oxytocin receptor gene were judged to be kinder than those with GA or AA versions. The difference? Those with GG variations used significantly more non-verbal empathetic gestures in their storytelling such as smiling and nodding. Kogan expects that this is what influenced the observers' judgements.
Further research will be needed to identify the effect of the different genetic variations on oxytocin levels.
Journal reference: Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.111265810