Researchers have identified a gene associated with empathy and sociability, and you can tell if someone has it just by watching their body language.
The altruism gene is actually a variant of the oxytocin receptor (OXTR) gene. People with one version of this gene, the GG variant, said that they experience high levels of empathy, positive emotions, and sociality. Plus, they exhibit more prosocial behavior. Individuals with an AA variant self-identified as having lower levels of positive emotions, empathy and parental sensitivity.
What's really interesting is that you can spot people who possess the altruism gene just from their body language, as new research revealed. Scientists took 23 romantic couples, identified one member's version of the gene, and then filmed them as their partner "described a time of suffering in their lives." 20 seconds of this silent footage was shown to strangers, who were asked to rate how kind, trustworthy, and caring they thought the person was. Of the 10 people marked as the most prosocial, six had GG variant, and of the ten marked "least trusted," nine had the AA variant.
There's a lot more that goes into making someone social, altruistic, empathic, and just generally nice than their genes, but this does show that there's a genetic factor involved, and it's something that we can pick up quickly and non-verbally.