Young children may use saliva as a clue to determine the strength of the relationships between people, scientists from the Massachusets Institute of Technology have suggested after a series of experiments.
It appears that any actions involving saliva, such as sharing food or kissing, are viewed by toddlers as indicators of the actors being in a strong relationship and sharing a mutual obligation of helping each other.
In case of distress, scientists now suggest, a baby is more likely to expect those sharing saliva to help each other than those who perform other kinds of actions together.
"Babies don't know in advance which relationships are the close and morally obligating ones, so they have to have some way of learning this by looking at what happens around them", says Rebecca Saxe, the John W. Jarve Professor of Brain and Cognitive Sciences, and a member of MIT's McGovern Institute for Brain Research. She is the senior author of the new study.
The experiments conducted by the scientific team to see whether their suggestions are right involved toddlers (16.5 to 18.5 months) and babies (8.5 to 10 months) who were offered to watch some interactions between human actors and puppets.
In the first experiment, an actor would share an orange with a puppet, and another actor would toss a ball back and forward with the puppet. Then, the puppet would display distress when sitting between the two actors, and the scientists would observe where the baby would look. According to earlier studies, the baby would look at someone who, as they expect, would be more likely to help. And it turned out that young children would look at the actor who shared the food with the puppet, not the one who shared a toy.
Another experiment involved an actor either placing her finger in her mouth and then into the mouth of the puppet, or placed her finger on her forehead and then onto the forehead of the puppet. When this actor would express distress when sitting between the two puppets, children who watched it were more likely to look toward the puppet with whom she had shared saliva.
Notably, the scientists managed to conduct the first stages of the study before the beginning of the pandemic and the increased attention to personal hygiene, including saliva-sharing.
"We actually know the results would have been similar if it hadn't been for the pandemic", Saxe says. "You might wonder, did kids start to think very differently about sharing saliva when suddenly everybody was talking about hygiene all the time? So, for that question, it's very useful that we had an initial data set collected before the pandemic".
According to the scientists, they intend to continue the study in order to determine whether the results would be similar with infants in cultures that have different types of family structures. Regarding adults, the researchers want to use functional magnetic resonance imaging (fMRI) to study what parts of the brain are activated during the decision-making process around the saliva-sharing interactions and the assessment of their impact on social relationships.