Have you ever cheered when a bad guy gets what he deserves in a movie’s closing scene? Or watched a child tattle on a classmate who broke the rules?

Scientists believe the urge to punish bad guys and reward good ones may be hardwired into the human psyche, and a new study suggests that even infants prefer to see punishment for an unkind act.

To test this urge for retribution, researchers put on different puppet shows for 100 babies in three age groups: 5 months old, 8 months old and 19 months and older.

The babies watched puppets behave positively or negatively toward one another – one elephant helped a duck open a box, while another elephant slammed the lid shut. Next, the children saw the “good” or “bad” puppets get rewarded or punished – a toy moose either gave a toy to the elephants or took the toy away.

When the babies were prompted to choose their favorite puppets, the researchers reported that most of the 8-month-olds preferred the puppets that had punished the “bad” puppets, while the majority of the 5-month-olds  preferred the moose that treated everyone kindly, even the “bad” elephants. The children 19 months and older acted similarly to the 8-month-olds, physically taking treats away from puppets who had mistreated others.

The study was published this week in the Proceedings of the National Academy of Sciences.

Study author Kiley Hamlin, a psychologist from the University of British Columbia, said the results offered some clues about exactly when humans develop a sense of justice, a factor that evolutionary psychologists say is critical to the function of society.

“Somehow between age 5 and 8 months, the babies get this much more nuanced perception, the ability to interpret circumstances,” Hamlin said. “It’s hard to argue that parents are teaching their children to punish at 8 months. It’s a very complex idea. If they are learning it, they’re doing it on their own, suggesting that there is some kind of system for learning it.”

Rahil Briggs, a child psychologist and director of the Healthy Steps program at Montefiore Medical Center in the Bronx, N.Y., said scientists knew very little about what happened in a baby’s brain in the earliest months of life. But she said that other complicated concepts started to become apparent to infants, such as a sense of self and the characteristics and motivations of others, at around 6 months old.

“There’s all sorts of things that we think start to emerge around that age that all point to the fact that babies become more aware of distinctions,” Briggs said. “I think as we continue to do this research that people are going to continue to be surprised and impressed by how sophisticated babies really are.”