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How Babies Detect Social Bonds

Infants as young as eight months can tell who will help others in distress.

Key points

  • Babies as young as eight months develop social cognition, the ability to think about others' thoughts, feelings, and relationships.
  • Babies can tell that people who imitate one another, share food, and share saliva have tight social bonds.
  • Babies expect socially bonded people who help one another in distress.

How Do Babies Learn?

How can you tell what a baby is thinking? One tried-and-tested method is surprising. Babies consistently look longer at things that surprise them, as if taking time to update their models of the world.

This is why peek-a-boo is so exciting for babies. Before children develop object permanence around six months of age–the knowledge that objects continue to exist even when we can’t see them–it appears as though you are literally disappearing and reappearing like magic. Older babies know your tricks and won’t gaze as long.

With this knowledge and paradigm comes most of what we know about infant cognition. Babies can learn to infer others’ preferences for toys, for example. If you show a baby someone choosing between two toys, say a car and a doll, they will originally have no expectation for what will be picked. They look at both options with the same level of interest. However, if you show someone playing with a car long enough that they habituate to it–become disinterested–and then repeat the trial, they will act surprised and look much longer if this person suddenly picks to play with the doll. It violated their learned expectations.

Despite what we know about infants’ learning for objects, until recently, little research was done on infants’ social cognition, our capacity to think about others’ thoughts, feelings, and relationships.

Babies can recognize other people and show a preference for their caretakers from an early age, but do they know anything about our own social preferences?

Infant Social Cognition

This question was recently put to the test by developmental psychologists in a series of experiments. In a recent article titled “Infants infer potential social partners by observing the interactions of their parent with unknown others” had parents play with puppets while their infants, ages eight to ten months, watched.

The first series of experiments had two basic conditions. First, imitation or non-imitation. Infants watched videos of parents and puppets making various movements or sounds that either imitated or did not imitate each other, with the idea that imitation is a form of social bonding. Second, parent or stranger. Infants watched either videos of their own parent interacting with the puppet or another child’s parent, a stranger.

Researchers then tested whether the infants developed a preference for puppets in different conditions. As expected, infants were most likely to choose puppets that had imitated their parents. When the puppet was imitating a stranger or shown with their parents but not imitating them, babies had no strong preferences for one puppet over the other.

Next, experimenters repeated this paradigm of showing babies videos, but with a new outcome measure. After watching puppets imitate or not imitate their parents or strangers, infants saw videos of the puppets all opening their mouths while a name was called out: either the infants’ name or another name. Again, as expected, infants were significantly more likely to look at the puppet that imitated their parents when their name was called, indicating that they learned that someone close to their parents was more likely to know their name and call out to them. When a random name was called out, infants had no expectation of which puppet was speaking.

Lastly, after watching voice-calling videos, babies watched a video of their parents crying out in distress while surrounded by puppets. Again, as expected, babies were significantly more likely to look to the puppet that called out their name when their parent was in distress. This signals that the babies truly understood that the puppets had social bonds with their parents and would be more likely to help them in distress.

Saliva Sharing Signals Closeness

Do these findings truly generalize to stating that infants can infer true social bonds, or is there something unique about imitation? This question was tested on 12-month-old infants in another study published this year, titled “Early concepts of intimacy: Young humans use saliva sharing to infer close relationships.

Yes, saliva sharing. This doesn’t mean that babies are licking people or tasting their spit to decipher how close they are, but it does mean that babies are constantly on the lookout for cues sent by others.

In this study, infants were shown videos of people interacting with puppets in one of four conditions: passing a ball back and forth, sharing food, patting their head then the puppet’s head, or putting a finger in their mouth, then in the puppet’s mouth, then back in their own mouth.

Infants then watched the person in the video cry out in distress while surrounded by puppets. Infants were significantly more likely to look towards the food-sharers or mouth-touchers than the ball-throwers or head-tappers. These results suggest that there is something special about saliva-sharing that infants recognize as a key marker of social closeness.

This makes sense. We are generally only comfortable kissing or sharing food with intimate partners, close family members, and close friends. We recognize this using our social cognition, and so do infants. Babies can detect social bonds as early as eight-twelve months old in the same ways we can.


Thomas, A. J., Saxe, R., & Spelke, E. S. (2022). Infants infer potential social partners by observing the interactions of their parent with unknown others. Proceedings of the National Academy of Sciences, 119(32), e2121390119.

Thomas, A. J., Woo, B., Nettle, D., Spelke, E., & Saxe, R. (2022). Early concepts of intimacy: Young humans use saliva sharing to infer close relationships. Science, 375(6578), 311-315.

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