According to a study, babies are able to tell who is in close relationships by the amount of saliva they exchange through sharing food and kissing.
Researchers at Massachusetts Institute of Technology (MIT) observed babies and toddlers as they watched interactions between human actors and puppets.
The interactions included a saliva exchange activity (sharing food), and another activity (passing a football).
The team discovered that infants and babies expected puppeteers to be close friends and have an ‘obligation to each other’ to share saliva.
The findings indicate that infants and babies are more likely to perceive two people as emotionally close to each other if they see them sharing a kiss or eating from the same plate.
Massachusetts Institute of Technology (MIT), researchers observed toddlers and babies as they observed interactions between puppets and human actors.
These activities are known as saliva exchange. They include sharing food and kissing, licking and putting one’s finger into another person’s mouth. However, such actions have declined in recent years due to Covid.
The study has been led by researchers at MIT’s McGovern Institute for Brain Research in Cambridge, Massachusetts.
Study author Rebecca Saxe stated that babies don’t always know which close relationships will be morally binding. Therefore, they must have a way to learn this from looking around.
People often distinguish between “thick” and “thin” relationships in human societies.
The strongest relationships between families are those that have strong attachments, obligations, and mutual responsiveness.
Anthropologists have found that those in close relationships tend to be more open to sharing bodily fluids, such as saliva.
‘That inspired both the question of whether infants distinguish between those types of relationships, and whether saliva sharing might be a really good cue they could use to recognise them,’ said MIT postdoc Ashley Thomas, lead author of the study.
The researchers watched interaction between puppets and human actors as toddlers aged 16.5 months to 18.5 month were observed.
In the initial set of experiments, a Puppet shared an orange and tore a ball between two actors.
According to experts from MIT in Cambridge (stock photo), infants can interpret signals such as sharing food or kissing to gauge whether someone is emotionally close.
The researchers then observed the infants and babies’ reactions to the initial interaction.
A 2003 study on non-human primates suggested that babies look first to the people who they are expected to assist.
A 2003 study found that baby monkeys crying cause other troop members to look at their parents as if they are expecting them to help.
The MIT research team discovered that infants and babies were more inclined to see the actor who shared food with their puppets, rather than the one who shared a toy when the puppet was distressed.
A second set of experiments was designed to concentrate more on saliva. The actor placed either her finger into her mouth, then in the mouth of the puppet or her finger onto her forehead, then on the forehead of his puppet.
Screenshots taken from the second experiment. This focused specifically on sharing saliva
The team discovered that children who saw the video of the actress expressing distress as she stood between two puppets were more inclined to gaze at the puppet with which they had shared saliva.
The researchers also used older children aged five to seven years for an additional experiment.
When presented with interactions between cartoon people, these children predicted that sharing utensils, or licking the same food item, would occur within nuclear families, whereas sharing toys and food would occur equally within friendships and families.
A nuclear family consists of two parents and their children, and differs from a single-parent family, a larger extended family or a family with more than two parents.
Researchers conclude that infants learn from saliva sharing and other cues, which may be an important cue to help them understand their social relations.
Thomas stated that the general ability to learn about social relations is extremely useful.
The distinction between thick or thin may be crucial for infants. This is especially true for human infants. They rely on adults more than any other species.
Researchers completed their initial set of experiments shortly before Covid lockdowns started. Later, they used Zoom to conduct further studies.
Researchers found that results were comparable before and after pandemics, which confirms that hygiene issues related to pandemics did not impact the outcomes.
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, whereas sharing toys and partitionable food would occur equally within friendships and families
Saxe stated that he was certain the outcomes would have been the same if the pandemic hadn’t occurred.
You might be wondering, how did the kids begin to see sharing saliva differently when everyone started talking about hygiene?
“So that’s it for this question. It’s extremely useful that we had an early data set prior to the pandemic.”
Zoom’s second study allowed researchers to reach a wider range of subjects, as they were not restricted to those whose families could visit the Cambridge lab during work hours.
The researchers plan to continue their work with infants from different cultures and family structures in the future.
Adult subjects will also be able to utilize functional magnetic resonance imaging, (fMRI), to examine which parts of their brains are responsible for making saliva-based assessments regarding social relations.
The new study has been published today in the journal in Science.