Scientists Figured Out When Human Babies Learn to Be Haters

They're not born with a distrust of strangers, but it's learned soon after.

puppet puppets show basketball sharing video

Babies begin to process language in the womb, so it’s no surprise that they prefer the familiar voice — and language — of their mother over that of a stranger’s. But babies being babies aren’t born haters: They may feel more positive about familiar voices, but that doesn’t mean they harbor negativity toward strangers straight from the womb. That problematic, very human tendency, researchers reported recently in Developmental Science, is a learned behavior.

And it’s learned pretty early in life.

In their study, the scientists from the University of British Columbia and Israel’s Bar Ilan University set out to determine how early in life babies learn to feel positively toward people who speak their language — their “in-group” — and more importantly, when they learn to feel negatively toward people in their “out-group.” They conducted six experiments on 456 infants aged eight to 16 months in order to compile their data.

As the researchers expected, their analysis showed that one-year-olds expect kindness from people who speak their native language, suggesting that these infants associate familiarity with positive expectations. But they didn’t have negative expectations for the out-group. That is to say, they didn’t assume the worst from strangers; rather, they were totally neutral, said Anthea Pun, Ph.D., a University of British Columbia psychologist who co-authored the study, in an interview with Inverse.

“We find in the current study that positivity for the familiar group does not automatically precipitate negativity towards an unfamiliar group,” said Pun. But she revealed that the negativity soon follows.

“The emergence of negative attitudes towards dissimilar groups have been found as early as age three.”

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Infants got used to the idea of an English speaker acting kindly sooner than any other condition.

While it’s clear that kids aren’t born with out-group biases, Pun says it’s not as obvious how environmental factors lead to their emergence later on. But studies have shown that five-year-olds “prefer stories that highlight positive things about their own group and negative things about out-groups,” she says. So, kids must learn to associate negativity with strangers somewhere between the ages of one and five.

She points out that many of the studies on bias and preference in children and infants are based on flawed methodology. Biases are a hard thing to study: In Pun’s study, she and her team used videos of puppet shows to gauge how babies reacted to different languages — in particular, by measuring how long their eyes lingered on characters that spoke in English (the babies’ native language) and French while doing kind (prosocial) or selfish (antisocial) things. What the researchers wanted to measure was how long it took babies to come to terms with what they were seeing. They reasoned that the longer it took for babies to look away from the video, the less the video matched up with the babies’ expectations.

The babies, who saw each of the four conditions in the video below, generally became habituated to the English-speaking, kind-acting puppets much more quickly than they did with all of the other options, leading Pun and her team to conclude that this scenario — that people who spoke a familiar language do nice things — was most in line with the babies’ expectations. That their response to the French-speaking, mean-spirited puppets was about the same as their response to all of the other scenarios implies that the babies felt neutral, not negative, toward them.

Pun points out most studies that claim to find negative biases in younger children force those children to choose between the familiar and the strange, and then jump to the conclusion that the kids not only have a preference for one but also actively avoid the other. This is problematic, she says, which is why Pun made it a point to gauge the babies’ reactions to a single condition at a time, so she could more clearly assess whether a preference for the familiar language is linked to a dislike of the unfamiliar language.

In follow-up studies, Pan exposed the infants to photos of positive and negative stimuli, like giant spiders or pictures of sweet fruit, pairing the photos with either English or French phrases. All of these additional experiments only further solidified their findings, and showed that, no matter what the unfamiliar stimulus was, the infants never associated it with the French language.

“This suggests that they processed the scenario where English speakers were nice more readily than when they were mean,” says Pun. “However, they habituated more slowly to French speakers behaving prosocially and antisocially. These rates were similar, suggesting they don’t evaluate them negatively.”


Previous research has suggested that infants exhibit a preference for familiar over unfamiliar social groups (e.g., preferring individuals from their own language group over individuals from a foreign language group). However, because past studies often employ forced-choice procedures, it is not clear whether infants’ intergroup preferences are driven by positivity toward members of familiar groups, negativity toward members of unfamiliar groups, or both. Across six experiments, we implemented a habituation procedure to independently measure infants’ positive and negative evaluations of speakers of familiar and unfamiliar languages. We report that by 1 year of age, infants positively evaluate individuals who speak a familiar language, but do not negatively evaluate individuals who speak an unfamiliar language (Experiments 1 and 2). Several experiments rule out lower-level explanations (Experiments 3–6). Together these data suggest that children’s early social group preferences may be shaped by positive evaluations of familiar group(s), rather than negative evaluations of unfamiliar groups.

Media via University of British Columbia