ARE SIGNS OF SHARED FEELINGS IN FROGS EVIDENCE OF EMPATHY?
The sight of their mates suffering seems to set off a stress response in monogamous poison dart frogs
In her lab, Dr Jessica Nowicki can often be spotted pinching and plucking a small female poison dart frog in the leg. Then she returns the amphibian to her terrarium home and waits for her male lover to share her pain. A wince, a jolt, a small leap towards his hurting partner will do.
While Nowicki, a neuro-ethologist at Stanford University, has yet to see such an outright display of concern, she’s discovered something similar. The male frog experiences a small spike in stress hormones once he’s reunited with his stressed counterpart: inside his body, he matches his partner’s emotional state.
This suggests frogs are capable of the most ancestral form of empathy, according to Nowicki’s new study published in the journal Royal Society Open Science – a finding that could upend our understanding of animal feelings, despite the difficulties in testing them.
“The first step is to stop assuming empathy isn’t there,” says Nowicki. “And the second is to be more holistic in how we can measure it.”
Figuring out whether non-human animals feel empathy is extremely challenging for scientists: animals don’t clearly communicate with us, and they can’t selfreport their feelings in a test. Empirically speaking, it’s also impossible to confirm whether the happiness one human says they’re experiencing is the same feeling another human knows to exist in their body.
“That certainly doesn’t mean that emotions don’t exist,” says Nowicki. “It just means that empirically they’re impossible to prove.” But emotions also have biological markers – they’re related to certain chemicals in the bloodstream and certain signals in the brain. These elements can be empirically tested.
Indeed, several studies have already tried to spot these markers of empathy in animals. In 2016, scientists found that prairie voles match the stress hormones of their partners and also console them by grooming them more if they notice they’re stressed. Birds have been suggested to change their song melodies and match those of partners in stress, and fish can tense up by simply watching their fish friends become agitated.
But seldom do scientists pose these queries to reptiles and amphibians. So Nowicki turned to poison dart frogs (Ranitomeya imitator). This species is monogamous – males and females rear their offspring together, communicating and helping each other out along the way – so Nowicki figured it would be easier to spot an emotional connection. She used the same experiment as the 2016 prairie vole setup.
Sure enough, when her team stressed out a random female frog and placed her in a terrarium with a male, nothing much happened. But when they stressed out a female frog and reunited her with her romantic partner, the male frog’s levels of corticosterone, a physiological biomarker of stress similar to cortisol, matched those of his lover.
“It was like, wow,” says Nowicki. “This is evidence of a frog rubbing off its emotional stress on another frog, therefore a form of empathy,” she says.
The fact the frog only reacts to his partner’s feelings means the transfer of distress isn’t just automated contagion – like the spread of alarm, a danger signal preparing the frog to deal with a potential threat, according to Dr Inbal Ben-Ami Bartal, a researcher of pro-social behaviours in animals at Tel-Aviv University. These findings are “a good example showing that the basic building blocks of empathy are shared across species,” says Ben-Ami Bartal.
The types of responses in amphibians could be very different than those of mammals. “I think we’d need to be open-minded about how to research this question in amphibians,” says Ben-Ami Bartal.
Dr Helen Lambert, an animal welfare researcher, agrees. “Empathy is a subjective experience. It may manifest in physical ways, but is still personal and unique to the individual,” she says. These new findings “may certainly be evidence of something more complex.”
This type of research might not be the right one, though, according to Dr Jessie Adriaense, a comparative psychologist at the University of Zurich, who penned a paper in 2020 on the challenges of measuring empathy across the animal kingdom.
She doesn’t believe the study is measuring what it claims to be. Pinching and poking the female frog didn’t induce a large amount of stress in her, according to the findings. So the male frog is matching a stable emotional state, but for there to be evidence of empathy, there needs to be a change in emotions in the first place, says Adriaense. The correlation between the female’s and male’s corticosterone levels isn’t very strong.
“I don’t think this can confidently say anything about emotion contagion in poison dart frogs,” says Adriaense, but it’s still absolutely crucial to continue looking for answers to these questions.
“Empathy is subjective. It may manifest in physical ways, but is still unique to the individual”