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(photo Source: Pexels) in nature, odors are important to many animals, who judge whether they are friends or foes by the smells of other animals.

Smell is the dog's "identity information". Each dog has a unique smell, which is the key information for them to communicate with other dogs. When two dogs meet, they can smell each other's buttocks and know each other's gender, age, what they ate in the morning, their health and even their mood.

Many cats mark their territory with urine or rub their fur on some landmarks near the territory to leave their own scent.

(photo source: wiki) Belding ground squirrels (Urocitellus beldingi) appear to be kissing, but in fact they can tell who their relatives are by sniffing complex information from the opposite cheek scent glands, and can even tell in seconds whether each other's relationship is too close to inbreeding.

In the process of human social interaction, smell is probably the most neglected detail. Do you remember why you got together with your best friend in the first place? Is it because of each other's bright smile? Or do you have common hobbies? Or is it because TA said something you were so proud of?

(photo Source: Giphy) in fact, smell also plays an important role in human social interaction. We often smell our own scent unconsciously, and we also consciously smell each other's smell when we meet someone for the first time.

The team of Israeli neurobiologist Noam Sobel realized that odor chemical signals were transmitted between people, but didn't know exactly how it happened, so they turned their attention to one of the most common movements when people come into contact with each other-the handshake.

They found that after shaking hands, the volunteers' hands ran to their faces inexplicably. To find out whether the volunteers were smelling their hands or just scratching their noses, the researchers connected the volunteers with instruments that measured physiological data to measure the air flow into the nose.

(photo Source: reference [4]) normally, volunteers put their hands next to their nose for 22% of the time, and some of the time the intake of air from the nose more than doubled, which is why they were smelling their hands.

After shaking hands with the same sex, the volunteers smelled the right hand, that is, the handshake, more than twice as often as before, while after shaking hands with the opposite sex, they smelled the left hand more often.

"We often think that sociochemical signals are transmitted more between members of the opposite sex, but this is not the case," Sobel said. "there are many examples of same-sex chemical signal transmission, such as the menstrual cycle of many women and friends gradually synchronized," Sobel said.

Inbal Ravreby, who is on his team, has found that we are more likely to choose friends with people who smell similar to us.

She thinks smell is very important in same-sex non-romantic relationships, especially in friendships that hit it off and hit it off. Sometimes we can establish friendships with others very quickly, and even before we get to know each other, we feel that we can be good friends, and this friendship can last for many years.

Loughby selected 20 pairs of such same-sex friends to do the experiment. she designed an "electronic nose" that can collect the smell from volunteers' clothes (authentic, no perfume or other influencing factors). Then analyze the chemical composition, and found that the chemical composition between friends is significantly more similar than that between random two people.

The "electronic nose" used in the experiment (photo source: reference [6]), but there are two reasons for this result. One is that the smells of two friends are indeed very similar, so they become friends, as predicted at first. Another reason is that the similar smell is the result of these two people being friends for a long time. If they live close to each other and often eat together, it is not impossible for them to smell closer and closer.

To figure out whether it was the smell that determined that they would be friends in the first place, Ruffby re-recruited some volunteers and asked the "electronic nose" to determine who might be friends.

The volunteers did not know each other, and played "mirror games" in pairs of the same sex, in which two people stood half a meter apart, one of whom acted and the other imitated. Ruffby uses scientific methods to judge their movement consistency and asks volunteers if they feel like they "hit it off" after the test.

Among the volunteers who did the Mirror Game (photo source: reference [6]), some of the combinations said they really felt like they had a tacit understanding with each other. The chemical composition collected through the "electronic nose" analysis also showed that these people were significantly more similar to each other than others, and their movements were more consistent when they played the Mirror Game.

So people with similar smells are really more likely to be friends. Loughby said there may be other unknown factors other than smell that affect the results, but she can currently rule out race, country of birth, mother tongue, values, education, marital status, smoking, caffeine intake, chronic health problems, hand habits, occupation or whether or not to wear glasses.

For a woman, she can rule out the effects of contraceptive use, irregular menstruation, and the start and end of the menstrual cycle.

(photo Source: giphy) the brain has been secretly judging by smell when we don't notice it. Other studies have shown that similar body odors induce similar patterns of brain activity, while exposure to strange body odors triggers a completely different brain response.

What makes human socialization different from other animals is that we have a very sophisticated language system, extremely complex thinking patterns, and there are too many factors that determine who we can be friends with in real life. this leads us to often ignore the role of smell, but we are obviously closer to other mammals than we think.

It turns out that chemistry really exists in the "chemical reactions" between people!

Reference:

[1] https://www.psychologytoday.com/us/blog/all-dogs-go-heaven/201811/scent-identity

[2] https://nautil.us/how-animals-use-smell-to-send-coded-messages-234605/

[3] https://en.wikipedia.org/wiki/Belding%27s_ground_squirrel

[4] Idan Frumin, Ofer Perl, Yaara Endevelt-Shapira, Ami Eisen, Neetai Eshel, Iris Heller, Maya Shemesh, Aharon Ravia, Lee Sela, Anat Arzi, Noam Sobel (2015) A social chemosignaling function for human handshaking eLife 4:e05154 https://doi.org/10.7554/eLife.05154

[5] https://www.newscientist.com/article/dn27070-after-handshakes-we-sniff-peoples-scent-on-our-hand/

[6] Ravreby I, Snitz K, Sobel N. There is chemistry in social chemistry. Sci Adv. 2022 Jun 24 Jun 8 (25): eabn0154. Doi: 10.1126/sciadv.abn0154.

This article comes from the official Wechat account: take Science Home (ID:steamforkids), author: everything, author: Ziv, revision: Shen Mengxi

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