TL;DR - A new study suggests that the ability to care about others may have originated millions of years ago in prehistoric animals before fish and mammals diverged on the tree of life. Researchers found that fish can detect fear in other fish and become afraid too, a behaviour regulated by oxytocin, the same brain chemical that underlies the capacity for empathy in humans. The study also showed that zebrafish pay more attention to fish that have previously been stressed out, a behaviour the researchers likened to consoling them. The research suggests that oxytocin's role in transmitting emotion is an "ancestral role" that may have been in place around 450 million years ago.