Oxytocin: Love Hormone Injections Turn Gray Seal Strangers Into Best Friends

grey seals
Wild gray seal. Oxytocin was found to increase social behavior in wild seals. University of St Andrews

Injections of the love hormone oxytocin have made wild seals friendlier toward one another, making them want to spend more time together and display far less aggressive behavior, which would normally surface among strangers.

The discovery shows oxytocin, which is involved in social bonding and sexual reproduction, encourages members of the same species to seek out one another and remain close—a finding that could have implications for human behavior and what happens when these social bonds break down.

Researchers at the University of St. Andrews gave wild gray seals intravenous injections of either oxytocin or saline. The dose of oxytocin was designed to mimic natural concentrations of the hormone, making it one of the lowest doses ever used to manipulate behavior.

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 one another, indicating a level of comfort or familiarity, and had fewer aggressive interactions.

grey seals
Wild gray seals. After oxytocin injections, seals wanted to spend more time together. University of St Andrews

Researchers say this is the first time it has been possible to show the effect of oxytocin on the relationships of wild animals, and that this pro-social behavior emerges naturally after the initial trigger.

"Despite using a minimal oxytocin dose, pro-social behavioral changes unexpectedly persisted for two days, despite rapid dose clearance from circulation post-injection," they wrote. "This study verifies that oxytocin promotes individuals staying together, demonstrating how the hormone can form positive feedback loops of oxytocin release following conspecific stimuli [stimuli from the same species], increased motivation to remain in close proximity and additional oxytocin release from stimuli received while in close proximity."

The scientists say their findings could have benefits for humans, potentially providing a way to prevent anti-social behavior. Study author Kelly Robinson said in a statement: "This study proves that oxytocin promotes individuals staying together, highlighting its fundamental role in forming and maintaining parental and social bonds.

"By studying the underlying physiology motivating bonding, social and parental behaviour, we can better understand what factors influence their existence in a variety of animals including humans. It also allows us to perceive what is happening when such bonds break down, why the frequently negative consequences associated with such losses happen, and how hormone treatments could be used to influence or avoid such events."