Empathy goes way back in evolutionary history, fish can sense each other's fear

Fish have the capacity to detect fear in other fish. They also react to the sensation by evoking fear in themselves. The new study suggests that animals can have complex emotional lives. This also means that a trait like empathy has a longer evolutionary history than previously imagined.

Scientists at the University of Texas conducted the experiment on zebrafish, a freshwater species native to South Asia. Findings have zeroed in on the brain chemical oxytocin as the responsible factor for contagious fear in fish. Surprisingly, the same hormone is responsible for empathy in humans as well, reported the journal Science.

The zebrafish were divided into different groups. One single fish was put in a tank. In another tank, a group of fish was put with a substance known to trigger fear. When they started erratic swimming due to fear, the single fish froze in fear. The single fish was seeing its peers through two layers of glass.

When the experiment was repeated with a genetically modified fish, the response to fear went down by 50%. When they were given a dose of oxytocin, the response changed.

Researchers think that if oxytocin is removed from the equation, the fish won't be mostly able to recognise fear in other fish. The subsequent reaction will also go away. The brain region responsible for regulating fear in fish is in some ways comparable to the emotional centre in the brain of mammals like humans. This suggests a common ancestor.

The last common ancestor between fish and humans existed 375 million years ago.

"The apparent concordance between mammals and fish of how oxytocin regulates empathetic behaviour raises the intriguing possibility that the mechanisms underlying empathy and some forms of emotional contagion may have been conserved since fish and mammals last shared a common ancestor," said Ross DeAngelis, one of the researchers.