In human society, people form "thick" relationships characterized by attachment, obligation, and mutual reaction. Studies of infants sharing dishes, kissing, or other interactive activities involving sharing saliva have found that infants are able to discern intimacy by sharing saliva.
(Source: Science)
Developmental psychology research shows that babies are initially unaware of which relationships are intimate and obligatory, so they use behavioral cues to infer different types of social relationships. People usually divide relationships into "pro" and "alienation", and "pro" relationships are characterized by strong attachment, obligation, mutual response, and a sense of oneness based on a common bodily substance that usually exists between close relatives. "Alienation" relationship is relative to the "pro" relationship, that is, superficial and ordinary communication, which is manifested in interpersonal communication as the estrangement of psychological level and physical distance.
Experimental flow and results
Recently, researchers at the Massachusetts Institute of Technology applied experimental techniques from developmental science to test whether children, toddlers, and infants can distinguish between various types of relationships, and whether sharing saliva can be a clue for them to identify intimate relationships. The findings were published in Science under the title "Early conceptsof intimacy: Young humans use saliva sharing to infer close relationships."
Research Achievements (Source: Science)
In the first experiment, the researchers had young children (5-7 years old) watch a series of cartoon characters interacting with each other in the following scene: "A girl standing on the grass drinking juice while playing with toys, when the girl's family and friends came over, asked who the girl should share food and toys with." "74% of children chose family, which illustrates how young children believe saliva sharing should occur in nuclear families.
The first experimental process (Source: Science)
Next, the researchers further analyzed the cognition of shared saliva and social behavior in toddlers (16-18 months) and infants (8.5-10 months). They had the children watch a video in which a blue doll alternately eats the same orange (meaning saliva sharing) with an actress and plays ball with another actress. The blue doll then sits between the two actresses, showing a sad and painful expression. When seeing someone in pain, about 80 percent of the participants would look at the person who had previously shared the food with the doll, hoping that the person would be able to comfort the doll.
Simulation of the second experiment (Source: Science)
This phenomenon also applies to other phenomena of sharing saliva, in order to pay more specific attention to the role of saliva, actresses and dolls have mouth-to-mouth interactions and forehead-to-forehead interactions. As the actress stands between two dolls to express pain, toddlers and babies look more at the dolls with whom they share saliva. As a result, young children perceive shared saliva as closer than others.
Second experimental interaction (Source: Science)
In addition, these interactive experiments were conducted before the outbreak of the new crown epidemic, after which researchers used the network to recruit a larger group of children, and collected more experimental data through online experiments, which also confirmed that infants and young children were more likely to share saliva with close people (such as relatives) than other people they met (such as friends or nannies). Finally, an ethnographic analysis shows that distinguishing between "pro" and "sparse" relationships around the world is a common behavior in human young children, and saliva sharing is a reliable clue to "pro" relationships.
But why sharing saliva can be discerning intimacy
What about reliable clues to relationships?
Exchanging saliva with strangers is likely to cause resentment, but this is not the case if people in intimate relationships share saliva. It has been suggested that disgust has evolved to prevent the spread of disease, such as when one person comes into contact with another person's viral bodily fluids.
In this study, Thomas et al.'s findings cross disciplinary boundaries and make people acutely aware of the unique role of saliva sharing in young children's understanding of human social relationships.
In summary, Thomas and colleagues used experimental methods such as interactive simulations and video animations to eventually find that children, toddlers, and infants believe that sharing saliva is more closely related than others; young children think that saliva sharing occurs in the nuclear family, while toddlers believe that people who share saliva are able to respond to each other in pain. These findings not only shed light on a toddler's understanding of the social structures around them, but also confirm the way young children expect intimacy.
Resources:
[1] Thomas AJ, Woo B, Nettle D, et al. Early concepts of intimacy: Young humans use saliva sharing to infer close relationships. Science. 2022 Jan 21;375(6578):311-315. doi: 10.1126/science.abh1054. Epub 2022 Jan 20. PMID: 35050656.