In 1959, psychologist Russell Church conducted a study on the empathy of rats. In the study, he trained the rats to push a lever to receive their food. Then, in a twisted change, he fixed the lever to a floor in the neighboring cage. Every time the rat would push the lever, the rat in the other cage would get an electric shock. Rats that had previously experienced shocks were very empathetic to the rat in the other cage.
Instead of selfishly pushing the lever and receiving its food at the expense of the other rat, the rat would quit pushing the lever and eventually starve to death rather than eat off of another rat’s suffering.