Scientists Gave Lions the Love Hormone Oxytocin To See What Would Happen

Scientists have given lions a dose of the love hormone oxytocin to see what impact it would have on this vulnerable apex predator.

Oxytocin is a hormone that, in humans, is associated with childbirth, bonding and breastfeeding. In animals, research over recent decades suggests it can play a role in social bonding. For example, research published in 2017 showed how injecting wild seals with oxytocin made them friendlier toward one another.

Lion numbers are currently plummeting, with an estimated 20,000 left in the wild. Lions are hunted by humans in retaliation for attacks on livestock and people, as well as preemptively to protect those living nearby. The species is also targeted by trophy hunters.

Lion conservation efforts often involve the relocation of individuals from areas where they are at risk from humans, as well as their reintroduction to parks. But lions are an aggressive predator and are highly territorial. This means bringing a new individual into an area where lions are already present can be risky.

brother lions
Stock image shows two lion brothers rubbing heads. Scientists found giving oxytocin to lions made them more tolerant of others. Getty Images

Scientists from the University of Minnesota wanted to see if oxytocin would promote social bonding among lions, as it does with other species. In their experiment at a wildlife reserve in South Africa, researchers lured lions to a wire fence with chunks of meat. Once close enough, they would spray oxytocin up their noses.

Findings showed that the 23 lions given oxytocin were more tolerant of others and were less territorial. "You can see their features soften immediately, they go from wrinkled and aggressive to this totally calm demeanor," Jessica Burkhart, who was lead author of the study published in iScience, said in a statement. "They totally chill out. It's amazing."

The distance between lions playing with a ball after oxytocin halved from about 22 feet to 11 feet, suggesting they became more tolerant of one another. Once food was introduced, the effect of the oxytocin disappeared.

Lion Conservation

Study co-author Craig Packer, from the Department of Ecology, Evolution, & Behavior, told Newsweek that lions are by far the most sociable cat species, showing obvious affection towards their companions. These are behaviors that are highly likely to release a pulse of oxytocin, he said.

"Our prior research on wild lions in the Serengeti showed that the lions' complex social system derives from a strong sense of 'us vs. them'—their incredibly close social relationships are largely driven by the dangers posed by neighboring groups—the larger group wins and pride mates work together to repel strangers from their territories—but their territorial response to strangers diminishes dramatically under the influence of oxytocin.

"Rather than roar in response to a stranger's roars, they remain silent. Usually, playing a roar is like pushing a button in the lions' territorial response, but oxytocin pretty much turns it off."

Sarah Heilbronner, another co-author and neuroscientist, told Newsweek there are many reasons why oxytocin might make animals more relaxed in what should be aggressive social situations. "One possibility is that oxytocin highlights the rewarding aspects of social interactions. We know that oxytocin impacts reward circuitry," she said. "Maybe it causes the good parts of social interactions to feel really good, and that can overshadow tension or vigilance."

Packer said their work could help wildlife facilities that need to promote social bonding between unfamiliar lions. "Prior techniques have largely relied on tranquilizers, antidepressants, etc," he said. "These work as long as the drugs are administered, but the effects often wear off after a few days or weeks."

Burkhart is now hoping to use oxytocin to help animals rescued from circuses and war zones. "The hope is that this will translate to animals being relocated in the wild, helping them to become more inclined to their new social environment so they're more curious and less fearful, leading to more successful bonding," she said in a statement.