Stress is the reason why we find it hard to empathise with someone we do not know, researchers suggest.
In separate tests in mice and people, empathy towards strangers increased when stress hormones were blocked by a drug.
Playing a fun video game with a stranger was found to have a similar effect to the drug.
The Canadian and American research team published their findings in Current Biology.
Previous studies have shown that the ability to feel or share someone else’s pain is not something unique to humans. Mice can feel empathy too.
But in both species, empathy is stronger between those that recognise each other and all but absent between those unfamiliar with each other.
Stress levels have also been shown to rise in both mice and people in the presence of strangers.