The Origins of Human Empathy May Go All The Way Back to The Ocean

A new study led by researchers from the Instituto Gulbenkian de Ciência in Portugal has provided evidence of the chemical mechanisms behind the spreading of fear among zebrafish, hinting that human empathy could have originated in our aquatic ancestors hundreds of millions of years ago.

Previous studies on zebrafish ( Danio rerio) provided insights into their transmission of alarm responses, presented as erratic and freezing behavior in individuals, and the elevation of cortisol levels in nearby observers.

To better understand the role the hormone could play in the transmission of fear in zebrafish, the researchers used mutant varieties that had broken versions of the chemical and two of its receptors.

Since zebrafish – like others in its order – release a chemical cue from their skin when injured that also provokes a response in nearby individuals, the team placed unfamiliar fish into separate tanks where they could still see others swim.

Adding oxytocin to the water or injecting it straight into select mutants changed their tune, further demonstrating the social hormone was responsible for their sensing of fear in others.

"However, to what extent the social contagion of fear observed in zebrafish and in mammals is homologous, or represents a case of convergent evolution, remains an open question," the authors admit.