In one of the fastest-growing areas in psychology, researchers are gaining insight into the mental processes of subjects that are barely able to communicate: babies. In recent years, innovative and playful experimental setups have suggested that infants as young as six months old have a sense of morality and fairness, and that 18-month-olds are capable of altruistically helping others.

Some of this research, though, has also shed light on babies’ dark side. A new study published in Psychological Science suggests that 9- to 14-month-olds exhibit a particularly unwelcome trait—in watching a puppet show, at least, they seem to prefer their own kind, and support puppets that pick on those who are different from them.

Because babies can’t communicate verbally, J. Kiley Hamlin of the University of British Columbia has pioneered the use of puppet shows to probe their psychology and better understand how they see the world. In this study, her research team put on an show in which 52 infant participants were led to identify themselves as similar to one of the characters in the show and different from the other.

To accomplish this, the researchers started off by asking the infants to pick a food, either graham crackers or green beans (a little surprisingly, a full 42 percent chose the vegetables). Then, the infants were shown a pair of rabbit puppets, one who liked graham crackers and one who liked green beans.

Once they’d solidly demonstrated each rabbit’s choice, one of them—either the one with the same preference as the infant observer, or the one with an opposite preference—would be randomly chosen to encounter a pair of new characters: one dog, termed a “helper,” and another, called a “harmer.” As the rabbit played with a ball and dropped it, the nice “helper” dog threw it back, but the mean “harmer” dog held onto the ball.

After both of the scenes were over, both dogs were presented to the infant, and the particular dog that the baby first reached for was interpreted as the character it preferred.

The results were a bit startling: When the infants had watched a play involving a rabbit with a food choice that matched theirs, 83 percent preferred the “helper” dog. When they’d watched a play with a rabbit who liked a different food, 88 percent chose the “harmer” dog. This held true regardless of the babies’ original food choices—the only thing that mattered was whether the rabbit’s identity, it terms of food choice, matched their own.

To further parse the motivations underlying the infants’ choices, the researchers conducted a similar experiment that involved a neutral dog that neither help nor harmed the rabbit. In this part of the study, the older infants’ preferences revealed that when watching rabbits who had different favorite foods than them, they not only liked “harmer” dogs more than neutral dogs, but strongly preferred even neutral dogs when compared to “helpers” (this was true among the 14-month-olds, but not the 9-month-olds). In other words, it seemed that they not only wanted to see the rabbit treated poorly, but also would rather see it treated neutrally than get some help.

Of course, when designing experiments for subjects that can’t use words to communicate, the simplest of variables could potentially throw off the results. It’s unclear, for example, if the researchers alternated which side the “helper” and “harmer” puppets appeared on, so the babies could have been influenced by their emerging sense of handedness. In the past, critics of such puppet show experiments have also charged that a baby merely reaching for one puppet or another might be an impulsive reflex, rather than reflecting an underlying moral judgement.

What’s clear, though, is that this experiment demonstrated a consistent reflex across the babies tested. While extrapolating this to mean that the babies are racist or bigoted is probably a step too far—for one, they were merely considering individual puppets, not groups of puppets with similar characteristics—it does raise interesting questions about the origins of xenophobia in an individual’s lifetime.