Young children, toddlers, and infants infer that individuals who share saliva through activities like kissing, sharing food or wiping drool are in so-called "thick" relationships – intimate bonds that people often share with family members.
The findings, based on experimental techniques from developmental science, reveal social clues youngsters use to inform their earliest understanding of the conceptual structure of family. Young children rely on adults for survival; however, not all adults are invested equally in the care of a particular child.
Therefore, it's important for children to be able to determine which relationships are uniquely close, or thick, at a very young age. Some researchers claim that younger children and infants must be sensitive to how relationships are communicated through distinctive behavioral interactions, such as deliberate and consensual sharing of saliva, which often occur in thick relationships.
To test this hypothesis, Ashley Thomas and colleagues performed a series of experiments using storybook-like cartoons, and people interacting with puppets. Thomas et al. found that children expected relationships in which saliva was shared to be closer than other relationships; young children (ages 5-7) expected such sharing to occur in nuclear families and infants and toddlers expected that people who shared saliva would respond to one another in distress.
Experiments in larger, more economically, geographically, and racially diverse sample of toddlers also found saliva sharing to be a cue for relationship thickness, which suggests that saliva sharing within thick relationships is culturally widespread.
"[Thomas et al.'s] findings reach across disciplinary boundaries and provide insight into how young children make sense of the complex social structures around them," writes Christine Fawcett in a related Perspective.
Thomas, A. J., et al. (2022) Early concepts of intimacy: Young humans use saliva sharing to infer close relationships. Science. doi.org/10.1126/science.abh1054.