Oxytocin, commonly known as the “love hormone,” plays a crucial role in the formation of emotional contagion, according to a recent study. The hormone is particularly essential in the spread of fear among zebrafish, highlighting the conserved aspect of emotions in vertebrates like fish and mammals. Empathy, which lets individuals recognize and respond to another individual’s emotional state, is common among social mammals. However, recent research suggests that empathy exists among several vertebrates, including fish. Emotional contagion, where individuals mirror the observed emotions and actions in others, forms the basis of complex empathic behaviors and is the most basic form of empathy, according to the study. The authors of the study discovered that wild-type zebrafish demonstrated a freezing behavior when exposed to distressed conspecifics. However, zebrafish without genes encoding oxytocin and oxytocin receptors did not show the same reaction, demonstrating that oxytocin was required for social fear contagion in zebrafish. This neuroscientific discovery implies that the underlying biological mechanisms behind empathy and emotional contagion might have been conserved since the last time fish and mammals had a common ancestor, which is roughly 450 million years ago.