Work

Four- to 6-month-old infants use saliva-sharing interactions to infer social intimacy

Year: 2026

Type: article

Abstract: People form distinctive relationships that are close, intimate, or “thick”. Across cultures, these relationships are often characterized by physical intimacy, including actions that involve sharing saliva, such as kissing or sharing foods or utensils. Recent research by Thomas et al. (2022) provides evidence that infants recognize saliva sharing as evidence of a thick relationship: Eight- to 10-month-old infants expect that two characters who share saliva will subsequently respond to each other's distress. To constrain theories of how knowledge of thick relationships emerges in development, the current studies tested for this expectation in younger infants, who have limited experience sharing food within the family and observing other people doing so. We tested 4- to 6-month-old infants in the same paradigms that Thomas et al. (2022) used to study 8- to 10-month-old infants. We replicated the findings from older infants in this younger sample; when 4- to 6-month-old infants saw a central actor in distress, they looked longer to an actor who had previously shared saliva with the central actor than to another actor who had not. These findings suggest that 4- to 6-month-old infants distinguish thick from other social relationships.

Source: Evolution and Human Behavior

DOI: 10.1016/j.evolhumbehav.2026.106960

Authors: Brandon M. Woo, Elizabeth S. Spelke, Rebecca Saxe, Ashley J. Thomas

Institutions: University of California, Santa Barbara, Harvard University, Massachusetts Institute of Technology

Language: English

Topic: Child and Animal Learning Development

Subfield: Developmental and Educational Psychology

Field: Psychology

Domain: Social Sciences

Open Access status: green