In 2014 a University of California researcher used a stuffed dog to show that animals are capable of jealousy. Professor Christine Harris asked dog owners to show affection for a stuffed animal in the presence of their pet. She found that three-fourths of the dogs responded with apparent envy. Some tried to get attention with touch or a gentle nudge. Others tried to push between their owner and the toy. A few went so far as to snap at their stuffed rival.

In a dog, jealousy seems heartwarming. In people, it can lead to less admirable results. Yet, as Moses and…