There is chemistry in social chemistry

Abstract

Nonhuman terrestrial mammals sniff themselves and each other to decide who is friend or foe. Humans also sniff themselves and each other, but the function of this is unknown. Because humans seek friends who are similar to themselves, we hypothesized that humans may smell themselves and others to subconsciously estimate body odor similarity, which, in turn, may promote friendship. To test this, we recruited nonromantic same-sex friend dyads and harvested their body odor. We found that objective ratings obtained with an electronic nose, and subjective ratings obtained from independent human smellers converged to suggest that friends smell more similar to each other than random dyads. Last, we recruited complete strangers, smelled them with an electronic nose, and engaged them in nonverbal same-sex dyadic interactions. We observed that dyads who smelled more similar had more positive dyadic interactions. In other words, we could predict social bonding with an electronic nose. We conclude that there is indeed chemistry in social chemistry.

Fig. 1.. The body odors of click friends are more similar than expected by chance.

(A) A PEN3 eNose was used to measure the volatiles that accumulated above a T-shirt in a jar (i.e., to measure the jar headspace). Photo credit: Inbal Ravreby, Weizmann Institute of Science. (B) Histogram showing 10,000 iterations of the average Euclidean distance (ED) between 20 same-sex random dyads in the eNose space. The distance between click friends is denoted by the red dashed line. (C) Histogram showing 10,000 iterations of the average ED between 20 same-sex random dyads in perceptual rating space. The distance between click friends is denoted by the red dashed line. (D) Pearson correlation between the difference in perceptual ratings and triangle test accuracy. The black line is the linear regression, and the gray area marks the confidence interval (CI) of the regression line. Each point is a click dyad (n = 20). (E) Histogram showing 10,000 iterations of the average difference in sniff duration when sniffing 20 same-sex random dyads. The distance between click friends is denoted by the red dashed line. (F) Perceived perceptual odor similarity for click dyads (x axis) versus random dyads (y axis). Each point is a rater (n = 25), and the point reflects the average of their 40 ratings. The diagonal line reflects the unit slope line (x = y), such that if points accumulate under the line, then the values are greater for click dyad similarity, and if they accumulate above the line, then the values are greater for random dyad similarity. The associated bar graph is the average perceived similarity. (G) Identical to (F) but for visual rather than olfactory similarity data.

Fig. 2.. Body odor similarity is related to clicking in the Mirror Game.

(A) A dyad playing the Mirror Game (a frame from a video recording taken by the hidden alarm clock camera that was on the table during the experiment). (B) Histogram showing 10,000 iterations of the average ED between 22 same-sex nonmutual clicking dyads who played the Mirror Game, represented in the eNose space. The distance between the 22 dyads who reported mutual clicking in the game is denoted by the red dashed line. (C) eNose-derived ED between all male dyads (n = 21) who played the Mirror Game. Dyads who reported a mutual click are outlined in black. (D) eNose-derived ED between all female dyads (n = 45) who played the Mirror Game. Dyads who reported a mutual click are outlined in black.

Fig. 3.. Body odor similarity is related to the quality of interaction in strangers.

Each panel is the Pearson correlation between the chemical differences in a dyad as determined by eNose versus 1 of the 13 measures of social interaction. Each blue circle is 1 of the 66 dyads who played the Mirror Game. The black line is the linear regression line, and the gray area marks the CI of the regression. The 13 measures are as follows: (A) including the other in the self as was measured in the IOS, (B) reading the partner’s mind, (C) understanding the partner, (D) willingness to meet again with the partner, (E) willingness to get to know the partner, (F) feeling close to the partner, (G) liking the partner, (H) feeling chemistry with the partner, (I) thinking that they could be good friends, and (J) feeling on the same wavelength.

Fig. 4.. Classifying mutual click dyads by eNose-derived body odor similarity.

An ROC classifying dyads who mutually clicked (n = 22, 14 females) or did not mutually click (n = 44, 31 females). The blue dot marks the performance of the leave-one-out cross-validation weighted KNN classifier. The dashed black line represents chance performance.