You need only 20 seconds to know whether a stranger is trustworthy, kind or compassionate, traits grounded in our genes, according to research published Monday.

The study authors concluded that a single genetic change can make a person seem more compassionate or kind to others. The findings aim to reinforce that healthy humans are conditioned to recognize strangers who may help them out in a tough situation. They also make way for genetic therapies for people who are not naturally sympathetic.

It's remarkable that complete strangers could pick up on who's trustworthy, kind or compassionate in 20 seconds when all they saw was a person sitting in a chair listening to someone talk, said Aleksandr Kogan, lead author of the study and a postdoctoral student at the University of Toronto at Mississauga.

The study, published Monday in the online version of the Proceedings of the National Academy of Sciences, builds up on a previous research on the human genetic predisposition to empathy.

The gene in question produces a receptor that latches onto the love hormone oxytocin. A single change in the receptor can result in higher or lower empathy, or how much a person is emotionally inclined to others.

What ultimately makes us kind and cooperative is a mixture of numerous genetic and non-genetic factors. No one gene is doing the trick. Instead, each of these many forces is a thread pulling a person in one direction or another, and the oxytocin receptor gene is one of these threads, Kogan said.

DNA samples were taken from two dozen couples. Researchers documented the couples as they talked about times when they had suffered. Researchers only recorded video of the partners as they took turns listening.

A separate group of observers, who did not know the couples, were shown 20-second video clips of the listeners and asked to rate who seemed most trustworthy, kind and compassionate, based on their facial expressions and body language.

The listeners who got the highest ratings for empathy, it turned out, possess a similar variation of the oxytocin receptor gene, known as the G version.

People can't see genes, so there has to be something going on that is signaling these genetic differences to the strangers, Kogan said. What we found is that the people who had two copies of the G version displayed more trustworthy behaviors -- more head nods, more eye contact, more smiling, more open body posture. And it was these behaviors that signaled kindness to the strangers.

Widely known as the cuddle or love hormone, oxytocin is secreted into the bloodstream and the brain, where it promotes social interaction, bonding and romantic love, among other functions.

Kogan pointed out that having the non-G versions did not render a person unsympathetic.

An earlier U.C. Berkeley study found that people with two copies of the G version of the receptor, one from their mother and one from their father, were more empathetic than study subjects with only a single copy of the G variant or other variants.