Babies can tell who has close relationships based on one clue: Saliva
Sharing food and kissing are among the signals babies use to interpret
their social world

Date:
January 20, 2022
Source:
Massachusetts Institute of Technology
Summary:
Neuroscientists have identified a specific signal that young
children and even babies can use to determine whether two people
have a strong relationship and a mutual obligation to help each
other: whether those two people kiss, share food, or have other
interactions that involve sharing saliva.



FULL STORY ========================================================================== Learning to navigate social relationships is a skill that is critical
for surviving in human societies. For babies and young children, that
means learning who they can count on to take care of them.


==========================================================================
MIT neuroscientists have now identified a specific signal that young
children and even babies use to determine whether two people have a strong relationship and a mutual obligation to help each other: whether those
two people kiss, share food, or have other interactions that involve
sharing saliva.

In a new study, the researchers showed that babies expect people who share saliva to come to one another's aid when one person is in distress, much
more so than when people share toys or interact in other ways that do not involve saliva exchange. The findings suggest that babies can use these
cues to try to figure out who around them is most likely to offer help,
the researchers say.

"Babies don't know in advance which relationships are the close and
morally obligating ones, so they have to have some way of learning this by looking at what happens around them," says Rebecca Saxe, the John W. Jarve Professor of Brain and Cognitive Sciences, a member of MIT's McGovern
Institute for Brain Research, and the senior author of the new study.

MIT postdoc Ashley Thomas is the lead author of the study, which appears
today in Science. Brandon Woo, a Harvard University graduate student;
Daniel Nettle, a professor of behavioral science at Newcastle University;
and Elizabeth Spelke, a professor of psychology at Harvard, are also
authors of the paper.

Sharing saliva In human societies, people typically distinguish between
"thick" and "thin" relationships. Thick relationships, usually found
between family members, feature strong levels of attachment, obligation,
and mutual responsiveness.

Anthropologists have also observed that people in thick relationships
are more willing to share 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 recognize them," Thomas says.

To study those questions, the researchers observed toddlers (16.5 to
18.5 months) and babies (8.5 to 10 months) as they watched interactions
between human actors and puppets. In the first set of experiments,
a puppet shared an orange with one actor, then tossed a ball back and
forth with a different actor.

After the children watched these initial interactions, the researchers
observed the children's reactions when the puppet showed distress while
sitting between the two actors. Based on an earlier study of nonhuman
primates, the researchers hypothesized that babies would look first at
the person whom they expected to help. That study showed that when baby
monkeys cry, other members of the troop look to the baby's parents,
as if expecting them to step in.

The MIT team found that the children were more likely to look toward the
actor who had shared food with the puppet, not the one who had shared
a toy, when the puppet was in distress.

In a second set of experiments, designed to focus more specifically on
saliva, the actor either placed her finger in her mouth and then into
the mouth of the puppet, or placed her finger on her forehead and then
onto the forehead of the puppet. Later, when the actor expressed distress
while standing between the two puppets, children watching the video were
more likely to look toward the puppet with whom she had shared saliva.



========================================================================== Social cues The findings suggest that saliva sharing is likely an
important cue that helps infants to learn about their own social
relationships and those of people around them, the researchers say.

"The general skill of learning about social relationships is very useful," Thomas says. "One reason why this distinction between thick and thin
might be important for infants in particular, especially human infants,
who depend on adults for longer than many other species, is that it might
be a good way to figure out who else can provide the support that they
depend on to survive." The researchers did their first set of studies
shortly before Covid-19 lockdowns began, with babies who came to the lab
with their families. Later experiments were done over Zoom. The results
that the researchers saw were similar before and after the pandemic,
confirming that pandemic-related hygiene concerns did not affect the
outcome.

"We actually know the results would have been similar if it hadn't
been for the pandemic," Saxe says. "You might wonder, did kids start to
think very differently about sharing saliva when suddenly everybody was
talking about hygiene all the time? So, for that question, it's very
useful that we had an initial data set collected before the pandemic."
Doing the second set of studies on Zoom also allowed the researchers to
recruit a much more diverse group of children because the subjects were
not limited to families who could come to the lab in Cambridge during
normal working hours.

In future work, the researchers hope to perform similar studies with
infants in cultures that have different types of family structures. In
adult subjects, they plan to use functional magnetic resonance imaging
(fMRI) to study what parts of the brain are involved in making
saliva-based assessments about social relationships.

The research was funded by the National Institutes of Health; the
Patrick J.

McGovern Foundation; the Guggenheim Foundation; a Social Sciences and Humanities Research Council Doctoral Fellowship; MIT's Center for Brains, Minds, and Machines; and the Siegel Foundation.

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========================================================================== Journal Reference:
1. Ashley J. Thomas, Brandon Woo, Daniel Nettle, Elizabeth Spelke,
Rebecca
Saxe. Early concepts of intimacy: Young humans use saliva sharing
to infer close relationships. Science, 2022; 375 (6578): 311 DOI:
10.1126/ science.abh1054 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220120140732.htm

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