Do people who grow up in different places find very different smells pleasant? Food cultures and memories contribute to our impressions of smells, but people living in distant societies may also share some preferences.
In a 2022 study, 225 people from nine societies ranked the same 10 odorants from most to least pleasant. The results showed substantial similarities in the groups’ average rankings, alongside considerable individual differences within each group. The study compared three perspectives, culture, molecules, and individuals, using the same task.
Looking beyond cities to compare diverse ways of life
Artin Arshamian and colleagues wanted to investigate whether odor pleasantness is determined by culture, reflects individual preferences, or is broadly linked to the properties of odor molecules.
Comparing only city dwellers can mean comparing people who have encountered similar foods and fragranced products, even if they live in different countries. The researchers therefore studied nine groups in Southeast Asia and Latin America with different geographical settings and subsistence practices. Their ways of life included forest hunting and gathering, coastal foraging and fishing, farming, and urban living in Mexico and Thailand.
The analysis of the nine newly studied groups included 225 people. For comparison, the researchers also converted odor pleasantness ratings given by 55 New Yorkers in an earlier study into rankings. It is important to note that this tenth group did not newly complete the same fieldwork task.
Ranking 10 odor pens from most to least pleasant
The study used 10 individual compounds, including vanillin, linalool, eugenol, 2-phenylethanol, and isovaleric acid. Rather than finished perfumes or foods, each pen-like device contained a single compound diluted to a specified concentration.
The 10 compounds were selected from an earlier US study of 476 compounds to span a wide range of ratings from unpleasant to pleasant. In each society, participants received instructions in their local language, smelled all the odors one at a time, and then arranged them from most pleasant to most unpleasant.
Rankings were used instead of scores because responding on numerical scales is not equally customary in every society. The initial presentation order was randomized, and attention was paid to the duration of each sniff and the intervals between presentations. Participants could smell the odors again while rearranging them.
The task reveals relative rankings: which of these 10 compounds participants found more pleasant. It did not ask whether they would actively want to use their top-ranked odor in everyday life.
The groups’ average rankings were very similar
When average rankings were calculated for each group, the mean cross-cultural correlation was high, at 0.82, indicating very similar orders. Similarities appeared for unpleasant as well as pleasant compounds, and the researchers also tested whether just one or two particular compounds were driving the results.
Specifically, averaged across all participants, vanillin, which evokes vanilla, and ethyl butyrate, described as having a peach-like smell, ranked toward the pleasant end. Isovaleric acid, which is also found in cheese and sweaty feet, ranked toward the unpleasant end. The figures in the original paper show that different people assigned different ranks to the same compound; not everyone put the odors in the same order.
At the individual level, however, rankings differed considerably. The similarity between two people’s rankings was only slightly greater when they belonged to the same culture than when they belonged to different cultures. Living in the same society does not make it possible to predict someone’s preferences precisely.
Regrouping participants into broader categories based on subsistence practices, such as hunting and gathering or farming, or by continent did not increase the amount of variation in rankings that could be explained. In this comparison of odors, the results did not show groups’ preferences diverging greatly on the basis of lifestyle or geography alone.
What do 41%, 6%, and 54% actually represent?
The researchers analyzed variation in rankings by separating differences associated with compound identity, differences in how compounds were rated across cultures, and variation not explained by those factors. The paper reports approximately the following proportions. Because the figures are rounded, they do not add up to exactly 100%.
- Variation associated with differences between odorants: about 41%
- Variation associated with differences in odorant rankings across cultures: about 6%
- Remaining variation, including individual differences: about 54%
The 54% is not a measure of purely personal preference in isolation. It includes fluctuations in perception and measurement noise associated with the task, as well as individual preferences. Nor does the 41% measure a genetic contribution: it corresponds to the tendency for many people to assign similar ranks to the same compounds.
The 6% also applies specifically to these 10 compounds, at these concentrations, in this ranking task. It does not establish that culture accounts for 6% of every kind of preference, including perfume purchases, food cultures, or memories associated with smells.
Can molecular information predict rankings in other societies?
The study did not stop at identifying similarities. The researchers also tested a model that predicted the pleasantness of the 10 compounds from their physicochemical properties.
The model was trained on 466 compounds from the earlier US dataset, excluding the 10 compounds used in this study. It linked numerous features calculated from molecular structure to US participants’ pleasantness ratings, then predicted ratings for the 10 compounds it had not been trained on. Those predicted values were converted into rankings.
These predicted rankings corresponded closely to each group’s average ranking. The paper reports that the model’s predictions were more strongly related to a group’s average ranking than the rankings of a randomly selected individual from the same culture. Because both the compounds used for training and the societies being studied differed, the results are difficult to explain simply as the model memorizing the same responses.
Molecular features contain information that can predict shared orders of pleasantness across cultures. This was another of the study’s main findings.
Shared does not necessarily mean innate
The results indicate that people share certain olfactory tendencies. This study alone, however, cannot distinguish whether those tendencies are innate or learned through experiences common to many people. The authors explicitly acknowledge this point.
People within the same group also have different experiences and life histories. Moreover, the study examined individual compounds at particular concentrations, unlike foods and perfumes that combine many ingredients and come with names and appearances. The condition of the equipment at the field sites and perceptual noise could also have contributed to variation in individuals’ responses.
An additional intensity-ranking task was conducted in five groups, confirming that pleasantness rankings were not explained simply by intensity. Examining these conditions carefully is important for distinguishing similarities from differences.
Summary
Comparing rankings of 10 compounds by 225 people from nine societies with existing US data revealed similarities in odor pleasantness across groups. At the same time, individual responses differed considerably, and cultural membership alone did not adequately predict a person’s rankings.
The close correspondence between the groups’ average rankings and a model trained on 466 other compounds also supports the existence of shared tendencies. Odor preferences have a common foundation, alongside differences between individuals. Rather than choosing culture or the individual as the sole explanation, this study considered molecular properties as well.
The study received funding from organizations including the Netherlands’ NWO, the US NIH, and the Swedish Research Council. The authors declared no competing interests.
References
- Arshamian, A., et al. (2022). The perception of odor pleasantness is shared across cultures. Current Biology, 32(9). DOI and original paper. Full text shared by a coauthor.
- Karolinska Institutet (2022). Research overview (consulted for descriptions of familiar smells).
