The Single Most Effective Way to Build Trust

Photo by Michael Dam
Photo by Michael Dam
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The Challenge: In an ever-expanding world, knowing whom to trust is increasingly difficult

The Science: Research shows that smiling increases trustworthiness — even of total strangers

The Solution: Greeting others with a genuine smile is an effective way to build immediate trust

S miles are an integral part of human and primate communications, and they usually convey a positive message. Genuine smiles (the ones that involve the muscles surrounding the eyes) induce positive feelings among those who are smiled at. From an evolutionary perspective, it is not entirely clear what messages smiles evolved to convey. A new study looks at the possibility that smiles evolved to signal trust in others.

To test how smiles may affect trust, the researchers used a common economic game in which a person has to decide whether to send a given sum of money to another person (I will refer to them as the senders). Once the money is sent, the sum is tripled. The other person, who is called the trustee, now has the option to divide the larger sum between him and the sender any way he wants to. So in principle, a person risks a low sum of money in the hope of getting a larger sum in return. The sender has no way to communicate with the trustee, but prior to sending the money to the trustee, the senders watched a video from the trustees who were trying to convince the senders to send them the money.

A total of 84 trustees participated in the study and recorded short clips telling the senders why they should send them the money. Each trustee faced at least two anonymous senders, so there were 198 senders. The trustees could decide not to return any money, return the original sum, or return 1.5 of the original sum (half of the total money). The sum of the original money ranged between $5-$10.

The researchers coded the video clips for the amount of genuine smiles shown by the trustees. The senders rated the trustees on various scales including trustworthiness, attractiveness, and intelligence. What the researchers found was that people who smiled were perceived as more trustworthy, more attractive and more intelligent.

How did smiles affect the amount of money the sender sent to the trustee and how trustees decided to divide it? Overall, smiles increased the likelihood that the sender would send the money to the trustee. Interestingly, when more money was involved and the stakes were higher, trustees smiled more and were perceived as more trustworthy. Finally, trusting those who genuinely smiled was worth it, as it resulted in higher earnings for the senders. Trustees who smiled more were also more likely to evenly split the (now) tripled sum in all these cases.

Why do genuine smiles increase trustworthiness? The researchers offer several possible explanations. Smiling decreases the visual field of the person smiling and hence, signals that the smiler is focused on one person. Smiling is also known to increase cooperation, as this study has explored.

The bottom line: If you want others to trust you, smile at them genuinly. It might benefit you more than you think.

This article first appeared in PsychologyToday.

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Gil Greengross
Gil Greengross is an evolutionary psychologist and anthropologist from the University of New Mexico. His interdisciplinary research bridges traditional fields of study such as psychology, anthropology and biology, and his studies focus on the adaptive value of humor and laughter, mainly in the context of sexual selection and mating. Dr. Greengross is also fascinated by the life and personalities of stand-up comedians as we can learn a lot from people who have extreme humor ability. His work has been featured in Psychology Today.
Gil Greengross

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