In her laboratory, Jessica Nowicki can often be found pinching and plucking the legs of tiny female poison dart frogs, then returning the frog to its terrarium home with its male partner, waiting for signs that the male is sharing his pain — a grimace, a flinch, or a small leap toward his injured partner.
Nowicki, a neurobehavioral scientist at Stanford University, has yet to see such overt signs of anxiety, but she has found a similar phenomenon: When male frogs are reunited with a stressed mate, their stress hormones rise slightly, internally synchronizing with their partner’s emotional state.
This discovery, as per Nowicki’s new research in Royal Society Open Science, suggests that frogs possess the most primitive form of empathy. This finding challenges the conventional understanding of animal emotions, despite the inherent difficulties in their examination.
“The first step is to stop assuming empathy doesn’t exist,” Nowicki says, “and the second is to think more holistically about how we measure empathy.”
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It is extremely challenging for scientists to ascertain whether non-human animals feel empathy since animals do not communicate clearly and explicitly with humans, and they cannot self-report their emotions during tests.
Even among humans, it is not possible to definitively confirm that one person’s happiness matches another’s subjective experience of happiness.
“That does not mean emotions do not exist,” Nowicki explains, “it simply means they are empirically challenging to prove.” However, emotions also possess biological markers tied to specific chemicals in the bloodstream and distinct signals in the brain, which can be empirically tested.
Several studies have tried to identify indicators of empathy in animals. For instance, in 2016, scientists observed that prairie voles mirrored their partners’ stress hormones, providing more grooming and comfort when they perceived stress.
Birds matching their songs’ melodies to their partners’ stress cues or fish observing excitement in other group members are examples of potential indicators of empathy.
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However, few studies have investigated reptiles and amphibians in this context. Nowicki decided to examine poison dart frogs (Ranitomeya’s Copycat) due to their monogamous nature, where males and females support each other in raising offspring, which she believed might reveal emotional connections. She utilized a similar lab setup as in her 2016 prairie vole study.
Indeed, when her team stressed randomly selected female frogs and paired them with male frogs, nothing notable occurred. Yet, when they reunited stressed female frogs with female frogs, the male frogs’ corticosterone levels, a stress biomarker similar to cortisol, mirrored those of their female partners.
“I was amazed!” Nowicki remarks, interpreting this as evidence of frogs expressing emotional stress through empathy.
The fact that frogs only respond to their partners’ emotions, not others’, indicates that distress transmission is not mere automatic contagion. Dr. Inbal Ben Ami Bartal, who studies prosocial behavior in animals at Tel Aviv University, calls these findings “a good example of shared basic components of empathy across species.”
While the frogs did not exhibit the anticipated behavioral changes, the possibility of emotional contagion remains plausible. Amphibian responses may differ significantly from mammals, and maintaining an open mind when studying this question in amphibians is crucial, according to Dr. Ben-Ami Bartal.
Animal welfare researcher Dr. Helen Lambert concurs, noting that empathy, as a subjective experience, can manifest physically but remains unique to each individual.
These new findings “could indicate something more complex,” but further studies are needed to understand this in amphibians, asserts Lambert.
However, this investigative approach may not be the most suitable, per Jesse Adriane, a comparative psychologist at the University of Zurich, who authored the 2020 paper discussing the challenges of measuring empathy across the animal kingdom.
Adriane believes that the frog study did not precisely measure what it claims to, as pinching and prodding female frogs did not induce significant stress. While the male frogs had stable emotional states, a consistent emotional change would be required to prove empathy, she contends.
Additionally, the correlation in corticosterone levels between male and female frogs is not strong.
“We cannot confidently conclude emotional contagion in poison frogs,” Adriane concludes.
Yet, it remains essential to continue exploring these questions to understand whether empathy is unique to humans.
About our experts
Jessica Nowicki is a research scientist in the Stanford University Biological Laboratory, focusing on prosocial behavior in early vertebrates.
Her work has appeared in journals such as Journal of Experimental Marine Biology and Ecology, Philosophical Transactions of the Royal Society, and Comparative Biochemistry and Physiology.
Dr. Inbal Ben Ami Bartel is a researcher in the Departments of Psychology and Neuroscience at Tel Aviv University, studying social neuroscience, prosocial behavior, and empathy.
Her research has been featured in publications like E-Life, Frontiers of Psychology, and Proceedings of the National Academy of Sciences.
Dr. Helen Lambert is an animal welfare scientist and the head of an animal welfare consultancy.
Her work has been published in journals like Applied Animal Behavior Science, Animal Welfare, and Animal.
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