From a baby’s point of view, you can really rely on a person with whom saliva is shared – for example, by taking bites of the same food.

Social relations are of crucial importance in human societies. And that starts early. For example, young children need to learn who they can count on to take care of them. Researchers have now discovered a signal that babies use to determine whether two people are close and thus have a mutual ‘obligation’ to help each other: the exchange of saliva.

close relationships

In human societies, a distinction is generally made between close and superficial relationships. A striking difference is that people in close relationships are more willing to share certain bodily fluids, such as saliva. “The person who shares saliva with you is usually close to you,” researcher Ashley Thomas told from.


You will probably find yourself in that. For example, you probably find it a lot less dirty to share a spoon with your brother than with a complete stranger. At the same time, you probably also feel a greater obligation to your brother to come to his aid in an emergency. When babies have just come into the world, they naturally do not yet know which relationships are intimate and therefore morally binding. They must have a way of learning this by looking at what is happening around them. A pressing question, however, is how young children do that; what do they pay attention to? “We wondered whether babies distinguish between different types of relationships and whether they might use saliva as a signal to recognize them,” Thomas said.


The researchers studied babies (aged 8.5 to 10 months) and toddlers (aged 16.5 to 18.5 months) while watching a play. In the play, a doll along with an actress ate an orange slice (meaning saliva was shared) and threw a ball with another actress. When the doll later started to cry, both the babies and toddlers looked first and longest at the actress with whom the doll had shared the orange slice, as if they assumed she would provide comfort sooner.

Experiment two

In a second experiment, the researchers focused more specifically on the exchange of saliva. An actress placed her finger in her own mouth first and then in the doll’s mouth. To follow up, the actress placed her finger on her own forehead and then on the forehead of another doll. Later, when the actress started to cry, all the children looked at the doll with whom she had shared saliva.


Of the study The researchers show that young children expect that those who share saliva will help each other when the need is high, much more than when only playing with toys together. So it means that babies use saliva exchange to find out who around them is most likely to come to their rescue. “The findings suggest that sharing saliva is an important signal that helps babies learn more about their own social relationships and those of those around them,” the researchers said.

Complex world

Sharing food, but also giving kisses, for example, can therefore be signals that younger children use to interpret the social world around them. This general skill for learning about social relationships is very helpful. “Babies are born in a very complex world,” Thomas says. “Part of that complexity comes from social relationships. But young children are able to distinguish between close and superficial relationships early on. One reason this is important to them is because human babies — who are dependent on adults longer than many other species — can find out who they can count on for their survival. Our findings now show that even young babies know a lot about their social world before they have much experience themselves.”

The researchers are not yet letting go of the subject. “We’re very interested in whether babies around the world respond to saliva sharing in the same way,” Thomas said. Not only do they want to study babies from other cultures, they will also examine different types of family structures. In addition, it is questionable whether babies are also more likely to share their own saliva with those close to them. Thomas still owes us the answer. “However, this is a good question that we hope to explore in future studies,” she concludes.