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The human body and mind are very intelligent machines that are built to succeed. One of the mechanisms that ensure our success in life is our ability to discern who we can and cannot trust, and this process begins very early in life for us.

As infants, our brain tries to decipher who we can rely on to take care of us. According to MIT neuroscientists, there is a very specific signal in our brain that helps us to decipher who we can trust. Based on their research, babies can determine whether or not two people are obligated to each other, and we can discern this based on whether or not they swap saliva.

Put simply, babies look around them to figure out and assess things. One of the things they look out for is two people who care for one another and the signal they are seeking to verify that is if they kiss, share food or interact in other ways that involve the sharing of saliva.

“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,” explains Rebecca Saxe, a professor at MIT and one of the senior authors of the new study.

It has been long known that humans can detect the difference between ‘thick’ and ‘thin’ relationships. Thick relationships are more like family, which have strong levels of attachment. This understanding pushed researchers to try to distinguish between those relationships and one of the ways they did this was to try to understand the cues which helped us recognize them, even early on.

So, the researchers observed toddlers as they observed human actors and puppets. They would go back and forth, allowing the toddlers to observe loving interactions and then distressed cries for help. When distressed cries for help took place, the toddlers would look at the person they expected to step in and help. and in most cases, they looked for the person who shared food with the puppet.