Bengaluru: Humans probably choose friends based on how similar someone’s body odour is to their own, say researchers from Israel who have conducted a trial to test their hypothesis.
The team found that in same-sex-pair interactions among strangers, those who smelled similar, as determined by sampling of odours, had more positive interactions. They also sampled body odours of non-romantic same-sex friend pairs, and found that friends smell similar to each other.
The team arrived at the hypothesis they wanted to test by comparing human behaviour with that of other mammals.
The study was conducted by researchers from the Azrieli National Institute for Human Brain Imaging and Research and Department of Brain Research, Weizmann Institute of Science, Rehovot, Israel. It was published in the journal Science on 24 June.
Body odour plays an important role in how all terrestrial mammals understand and respond to other individuals. This is evident in how dogs and other pets smell each other by way of introduction.
Humans too are known to sniff each other’s skin and hair, but the purpose of this olfactory input continues to be unclear.
Because humans tend to immediately bond with others who are similar to them to form friendships, the authors began to investigate body odour similarities among such instantly “clicked” friends and the influence olfactory input has in how we form relationships.
“We conclude that there is indeed chemistry in social chemistry,” write the authors in their paper.
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‘Click friendships’
Human friendships over time form due to various factors such as age, race, religion, education, personalities, values, and even physical appearance, neural patterns, and genetic makeup of individuals.
But “click friendships”, where people hit it off instantly, are catalysed by unfamiliar factors, one of which is theorised to be the smell of an individual.
Humans are said to not only sniff others, but also themselves constantly, subconsciously becoming intimately familiar with their own natural odour. We are also strongly bonded to the odours of our biological family unit, preferring to engage in romantic relationships with those having similar or overlapping scents.
After giving birth, a mother is capable of identifying the scent of her newborn over the smells of other babies, indicating that a child’s body odour is a signalling mechanism to invoke parental care.
Even in social interactions involving contact, such as handshakes, scientists have observed subconscious sniffing behaviour, potentially representing chemosignal processing.
People are also capable of “sensing” danger or discomfort from body odours, feeling a sense of fear around a person. A happy emotional state of mind is also communicated through body odours via chemosignals, studies have found.
Following data from such studies, the scientists theorised that humans might be selecting “click” friends based on how familiar a stranger’s body odour is compared to their own.
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Experiments and findings
The authors divided their experiment into different parts.
First, they confirmed the existence of the “click friendship” phenomenon. They recruited 235 same-sex non-romantic click friends for the study, who all had formed instantaneous friendships, and asked them to describe what a click friendship was in their own words.
They then conducted a six-month-long social media recruitment campaign for click friend pairs, ending up with a total of 10 same-sex friendship pairs each among men and women. These 40 participants affirmed their click friendship, and described it in the same terms as the earlier group of participants.
Their body odours were then harvested, and researchers found that when compared to other random individuals’ smells, click friend pairs had similar odours.
Next, the team recruited 24 “smellers” wearing nasal cannula and spirometer to measure air flow, who were presented with the 40 smells from the previous group. These smellers were given smells of three (a “triangle test” to find an outlier): A click pair and an extra person, and were asked to rate the smells for similarity and sexual attractiveness, and also identify the extra person.
The authors found that while individuals could not tell who a click pair were, they rated the smells of a click pair as more attractive in each triangle. Additionally, the smellers also sniffed the click pair odours for approximately the same amount of time, while they took longer or shorter to process the outlier odour.
Lastly, the researchers recruited 17 strangers and collected their body odours. They asked pairs of participants to mirror each other’s movements without talking, standing physically very close to each other. The movements enabled dispersion of body odour. The participants were then asked to rate their quality of interaction and who they thought they “clicked” with.
Individuals from 22 pairs — combinations among the 17 individuals — self-reported “clicking” without having had a verbal exchange, and the researchers found that these individuals had similar body scents to the person they thought they clicked with. Chemically similar smell pairs also reported higher quality of interaction.
The authors note that the chemical similarity between “click pairs” was not explained by race, country of birth, mother tongue, values and principles, education, marital status, smoking/alcohol/caffeine consumption, health issues, profession, or any other factor.
The paper quotes Dostoevsky’s Crime and Punishment, saying: “Here… perfect strangers may begin to interest us at first sniffs rather than at first sight alone.”
(Edited by Nida Fatima Siddiqui)
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