8-Month-Old Babies Recognize Wrongdoers and Seek to Punish Them

Human beings may be a savage species when we want to be, but we’re also an exceedingly moral one, with a highly evolved sense of right and wrong, good and bad, crime and consequences. Few things illustrate this better than our practice of third-party punishment: meting out penalties against malefactors who have done us no personal harm. The entire criminal and civil justice system is built around judges and juries punishing offenders who have wronged not them, but another.

An instinct for third-party punishment appears early in life—think of preschoolers tattling on classmates who have broken a rule or taken a toy from someone else—but just how early has been unclear. Now, a study published in June in Nature Human Behavior offers an answer. According to research led by investigators from Osaka University and Otsuma Women’s University, in Japan, third-party punishment behavior may begin in babies as young as 8 months old. The researchers say it’s evidence that morality may be innate.

Since it is impossible to know what’s going on in a pre-verbal baby’s head by asking them, the study involved familiarizing 24 8-month-old babies with a simple video game, in which anthropomorphized shapes—squares with eyes drawn onto them—move about a screen interacting with one another. Where the babies’ own eyes moved was recorded by a gaze-tracking device, and as the babies watched the shapes move, they learned an important feature of the game: if they let their gaze linger on one figure for long enough, a square without eyes would fall from the top of the screen and crush it.

Once the babies had learned that feature of the video game, the researchers made things more complex. Now, as the babies watched, one of the squares with eyes would occasionally misbehave, colliding with another one and squashing it against the edge of the screen. After several such incidents, the babies started to respond, with roughly 75% of them directing their gaze at the wrongdoer and holding it there until the crushing square would fall from the sky and destroy it—effectively administering a penalty for its misbehavior.

“The results were surprising,” said lead author Yasushiro Kanakogi in a statement that accompanied the study’s release. “We found that preverbal infants chose to punish the antisocial aggressor by increasing their gaze toward the aggressor.”

That, at least, is what the study suggested, but there were other possible interpretations. Suppose, for example, the babies were not trying to punish the aggressor, but rather their gaze was simply drawn to it because it was the most active square on the screen. To test that theory, the investigators trained another 24 babies of the same age on a game in which a square would still fall on the aggressor, but it would fall slowly and harmlessly, without crushing—or punishing—it. When the same test was run under those conditions, the babies stared much less predictably at the wrongdoer, with the number who directed their eyes that way falling to the 50% or lower range.

Similar lower results were achieved when the researchers re-ran variations on the study two more times with two more groups of 24 babies each. In one trial, gazing at the wrongdoer caused the crushing square to fall only half the time—making the punishment less reliable. In another, the eyes were removed from the character squares, making them less anthropomorphic. In both of those trials too, the babies’ gazed much less frequently at the malefactor after it misbehaved. Finally, recruiting yet a fifth group of babies, the researchers re-ran the original experiment, with anthropomorphized squares getting crushed every time the babies gazed at them. The babies reacted accordingly, with the frequency of gazing at a misbehaving character rebounding to the levels in the first experiment. The babies, it seemed, did not always like what they saw and were acting as judge and jury to set a wrong right.

The results, the researchers believe, point to the likelihood that third-party punishment is less learned than it is evolved, a part of a universal moral grammar with which many psychologists and ethicists believe human beings are born.

“The observation of this behavior in very young children indicates that humans may have acquired behavioral tendencies toward moral behavior during the course of evolution,” Kanakogi said in a statement. “Specifically, the punishment of antisocial behavior may have evolved as an important element of human cooperation.”