Some close relationships exhibit distinctive saliva-sharing interactions such as sharing food or kissing. New research published in Science found that infants and toddlers infer close and supportive relationships between those who engage in saliva sharing interactions.
People categorize social relationships by strength. Relationships that feature strong attachment, obligations, and mutual responsiveness (i.e., “thick” relationships) tend to be seen between close genetic relatives but can also exist outside the nuclear family. These relationships are also characterized by distinctive interactions such as those that transfer saliva (i.e., sharing food utensils).
“Here we apply experimental techniques from developmental science to test whether young children, toddlers, and infants do indeed infer that two individuals who share saliva are likely to be in a thick relationship,” wrote study author Ashley J. Thomas and colleagues.
In their first experiment, 113 children (aged 5 to 7 years old) were presented with interactions between cartoon people. Participants predicted that sharing utensils or licking the same food item would happen within a nuclear family, while sharing toys and food would happen both in friendships and in families. This suggests young children recognize this distinctive interaction as being indicative of a close relationship like that in a nuclear family.
In their next experiments, 27 toddlers (aged 16.5-18.5 months old) and 20 infants (aged 8.5-10 months old) saw a puppet alternately eat from the same orange slice as one actress (saliva sharing interaction) and play ball with another actress. The puppet then is seated between the two actresses and exhibits distress. Researchers recorded which actress the children look toward first and longer to measure which actress they expected to react to the puppet’s distress.
Results show both toddlers and infants looked at the actress who shared the orange slice first and longer than the other actress. In larger iteration of this study with a more racially diverse sample of 118 toddlers, the results were replicated. Children looked first and longer at the one who shared food with the puppet.
In their third series of experiments, researchers removed the element of food sharing and had the actress deliberately transfer her saliva to the puppet’s mouth using her finger. When interacting with a second puppet, the same actions were undertaken but with the puppet’s forehead. The actress then showed distress and researchers recorded their gaze toward each of the puppets.
Toddlers looked first and longer toward the puppet from the mouth interaction compared to the forehead interaction. Infants’ first looks were equal between the two puppets, but they looked longer at the mouth interaction puppet. When the actress was replaced with a new actor, infants and toddlers looked first and longer at the forehead interaction puppet.
A follow-up study of parents of infants and toddlers also found that parents expressed comfort with saliva-sharing interactions (i.e., sharing a utensil, drinking from the same cup) only in “thick” relationships.
“School-aged children’s judgments about saliva sharing are likely reinforced by explicit prohibitions (particularly during a pandemic), but similar intuitions appear to originate earlier and to generalize beyond the content of verbal rules motivated by hygiene,” the authors concluded. “We hypothesize that an early intuitive distinction between thick and thin relationships allows infants to rapidly learn the distinctive behaviors that occur in these relationships in their social environment.”
The authors cite some limitations to this work such as not including more measures to fully assess whether thick and thin relationships are thought of as distinct. Further, some interactions involving saliva transfer are aggressive (i.e., spitting on a person) and it was not assessed whether toddlers and infants can appreciate this difference.
The study, “Early concepts of intimacy: Young humans use saliva sharing to infer close relationships“, was authored by Ashley J. Thomas, Brandon Woo, Daniel Nettle, Elizabeth Spelke, and Rebecca Saxe.