For decades, empathy was considered a uniquely human trait—or, at most, one shared by the primates closest to us. The last fifteen years of neuroscientific research have dismantled this belief piece by piece, providing experimental evidence involving rodents, elephants, cetaceans, and even fish.
Pain That Is Transmitted Among Mice
In January 2021, a research team at Stanford University led by Monique Smith, along with Naoyuki Asada and Robert Malenka, published a study in *Science* that changed the perspective on the neurobiology of animal empathy. The researchers observed that a brief social interaction between two mice—one of which was experiencing inflammatory pain or the analgesic effects of morphine—resulted in the transfer of that state—pain or relief—to the other mouse. The scientists demonstrated that the anterior cingulate cortex and its projections to the nucleus accumbens are responsible for this social transfer, while another circuit—the one leading to the basolateral amygdala—manages the transmission of fear.
Malenka summed up the significance of the discovery in a sentence that has become famous among experts: “You actually relieved this animal’s pain simply by letting it be with another animal whose pain had been relieved.”
The Rat, the Trapped Friend, and the Chocolate
Ten years earlier, another study had already shaken the world of comparative psychology. Inbal Ben-Ami Bartal, Jean Decety, and Peggy Mason, from the University of Chicago, placed a free rat in an arena alongside a cage-mate trapped inside a transparent tube that could only be opened from the outside. Within a few days, the free rat learned to manipulate the mechanism to free its companion.
The most frequently cited part of the experiment is the one in which the researchers presented the rat with a choice: to open the container with its trapped companion or the one filled with chocolate chips, which rats love. The result, quoted verbatim from the study: “When the release of a cage mate was pitted against chocolate contained in a second container, the rats opened both containers and generally shared the chocolate.” According to the researchers’ reports, some animals picked up the chocolate chips with their mouths and placed them near their newly freed companion.
Reconciliations Among Chimpanzees and Comfort Among Elephants
The pioneer of this line of research remains Frans de Waal, who, in 1979, together with Angeline van Roosmalen, documented for the first time the behavior of reconciliation among chimpanzees at the Arnhem Zoo: after a conflict, the former adversaries tended to seek each other out more than they did third parties, through kisses, hugs, and vocalizations of submission. Decades later, a second line of research demonstrated that these gestures are not merely social rituals: they measurably reduce stress-related behaviors, such as compulsive scratching, in the animal receiving them.
A similar approach led de Waal, together with Joshua Plotnik, to study Asian elephants at a camp in Thailand. In the study published in PeerJ in 2014, the elephants were significantly more likely to establish direct physical contact and vocal communication with a companion after a stressful episode than during control periods. Even animals that witnessed the scene—without being directly involved—tended to bond with one another, mirroring the emotional state of the first elephant in distress, a phenomenon the researchers call “emotional contagion.”
Even fish sense others’ fear
The most surprising discovery, chronologically speaking, concerns fish. A study published in *Science* in 2023 demonstrated that zebrafish exhibit a form of fear contagion when they observe a fellow fish in distress, and that oxytocin—the same hormone involved in social and empathetic bonds in mammals—is both necessary and sufficient for this response. According to the study, the brain regions involved are homologous to those active in rodents during similar processes.
Taken together, these studies reveal something broader than mere curious individual incidents: the neurobiological foundations of empathy are not a recent evolutionary development in primates, but a deeply rooted trait preserved across species that are very distantly related on the tree of life.
