The kindness of individual human beings comes down to the presence of a certain gene trait, according to researchers.
Scientists from Oregon State University said that compassion is linked to the body's receptor gene of oxytocin, and strangers are able to quickly tell whether a person has this gene or not.
Findings of the study were published in the Proceedings of the National Academy of Sciences.
According to the report, nine out of ten people who were judged by a neutral observer to be "least trusted" were found to have the A version of oxytocin, with six out of ten described as "most prosocial" having the GG genotype.
Before the study, people were tested to see whether they had the GG, AG or AA genotypes for the rs53576 DNA sequence of the gene, with those with the G allele judged to be more empathetic and kind, while those with AG or AA were found to be less positive overall.
Aleksandr Kogan, a postdoctoral fellow at the University of Toronto, lead author of the study, said: "Our findings suggest even slight genetic variation may have tangible impact on people's behaviour, and that these behavioural differences are quickly noticed by others."
"The oxytocin receptor gene in particular has become of great interest because a select number of studies suggest that it is related to how prosocial people view themselves.
"Our study asked the question of whether these differences manifest themselves in behaviours that are quickly detectable by strangers, and it turns out they did," he added.
Earlier this year, it was suggested by US neuroeconomist Paul Zak that social and political issues could be solved if people have a higher level of oxytocin in their body.
Speaking to the Guardian, he said: "Oxytocin is primarily a molecule of social connection. It affects every aspect of social and economic life, from who we choose to make investment decisions on our behalf to how much money we donate to charity. Oxytocin tells us when to trust and when to remain wary, when to give and when to hold back."