The researchers used newly weaned seal pups that had never met before—adults could not be used, the authors note, because they could not be certain the seals were complete strangers. After the injections, seals were observed for behavioral changes.

Their findings, published in the Proceedings of the Royal Society B, showed the oxytocin group were significantly friendlier for up to two days after the initial dose—long after the effect of the hormone would have worn off.

Pups spent “significantly more time in close proximity” after oxytocin treatment. They also performed fewer checks on each other—indicating a level of comfort or familiarity, and had fewer aggressive interactions.