Babies Think We Share Our Food with the Ones Close to Us
Assessing how close two people are can be tricky for the outside observer. Imagine how challenging it must be for babies who haven’t yet had a lot of social experience apart from the relationship with their caregivers. CEU Babylab researchers Beyza Ciftci, Jonathan Kominsky and Gergely Csibra have just published a successful replication of a study about food sharing as a potential cue that helps babies identify close relationships.
In our social circle, we form various relationships with different people. For example, with some of our colleagues or the person at the bakery we visit daily, our interactions are limited to saying "good morning" when we see each other. With others, we might have connections that involve having lunch together at work, meeting for coffee occasionally, or borrowing a book from them. There are also some people we want to share all our important life events with, the ones we can always count on in difficult times. We call what we have with this last group of people close relationships.
Although we typically have such relationships with our family members, who we have close relationships with can be independent of where and how this relationship is established. We can have close relationships with our colleagues, romantic partners, or friends from school. This makes it a complex task for an outside observer to understand which people are close. This task is even more challenging for little ones who do not have much relationship experience beyond their bond with their caregivers. On top of all this, common practices in relationships can vary across cultures. Despite all these difficulties, can young babies understand which people have close relationships with each other?
Some researchers suggest that there might be some hints for certain relationships that do not vary across cultures. Such hints can make it easier for us to identify relationships. For example, differences in physical size in the animal kingdom can be a hint of dominance relationships. Similarly, sharing the same piece of food can be a hint for close relationships because it involves sharing saliva. Babies may notice these hints at a young age and could use them to assess who has close relationships with whom in their environment.
A recent online study by Ashley Thomas (Harvard University) and colleagues showed that babies can indeed use sharing the same food piece as a hint to identify close relationships. In our lab, we decided to see whether this finding is reproducible in a more controlled lab setting. The CEU researchers showed babies the same video materials that were used in the original study, but used eye-tracking to monitor their gaze instead of recording their looking behavior on video and analyzing it later. The eye-tracking technology allowed them to measure accurately where babies are looking and for how long while observing social interactions.
The 8-to-10-month-old participants were shown videos of two women interacting with a blue puppet in two different ways: one of them chewed the same piece of orange as the puppet, while the other woman played ball with the puppet.
The researchers wanted to know if the babies had an idea which woman had a closer relationship with the puppet. To assess this, they checked whom the babies expected to help the puppet in need. They showed the babies another scene where the puppet started to cry and then measured which woman the babies looked at more.
Puppet crying
The results showed that babies looked longer at the woman who previously shared her food with the puppet, probably expecting this person to comfort the puppet in distress. This suggests that babies formed expectations about the nature of the relationships between the puppet and the two people based on the interactions they witnessed between them: they assumed that food sharing implied a closer relationship than playing together. This is a new area of research, and it is still too early to conclude that sharing food is a general hint about close relationships for babies. However, these findings suggest that young brains use these observations to figure out the relationships among the people around them.
Original paper: Ciftci, B. G., Kominsky, J. F., & Csibra, G. (2025) Do infants use cues of saliva-sharing to infer close relationships? A replication of Thomas et al. (2022) Royal Society Open Science 12240229 http://doi.org/10.1098/rsos.240229
Cited: Thomas, A. J., Woo, B. M., Nettle, D, Spelke, E. S., & Saxe, R. (2022) Early concepts of intimacy: young humans use saliva sharing to infer close relationships. Science 375, 311–315. doi:10.1126/science.abh1054
