The sense of smell in humans: characteristics and function

To what extent is it true that the sense of smell in humans is underdeveloped?

The human sense of smell can be truly astounding.The sense of smell in humans can be truly amazing, even though the idea that it is a useless, vestigial, atrophied sense, more typical of animals than of Homo sapiens, a species too rational to be guided by it, is still widespread and deeply rooted.

Since ancient times, and especially since the 19th century, smell has been seen as a sense that gives us little information, but thanks to the most recent research in cognitive sciences, we know that this is not the case. Moreover, cross-cultural studies have shown that there are many languages in which smell is very relevant.

Next we will talk about the sense of smell, the anatomical structures that make it possible, why it is believed to be underdeveloped in humans and we will also see cases of cultures where it is of great importance.

How is the sense of smell in the human being?

Many people continue believing that human beings have an underdeveloped sense of smell and that in no way can we compete against the human sense of smell. and that we can in no way compete with other animals, such as dogs or mice, when it comes to identifying odors. For a long time it has been thought that this sense was vestigial in our species and that throughout evolution it has been relegated mainly by the improvement of our sight and hearing.

This has been a very common belief but, thanks to cognitive science and taking a cross-cultural perspective, it has been proven false. The idea (Western, by the way) that humans cannot smell very well is an old myth, whose origins date back to the 19th century and which has greatly influenced both science and popular culture.

While it is true that there are many species that are better at identifying odors than we are, our sense of smell is as good as that of many other mammals. Humans can discriminate around a trillion different odors (once thought to be only 10 billion). (previously thought to be only 10,000) and, despite having a relatively small olfactory bulb, our abilities to recognize odors are better than the scientific community first thought.

How does it work?

Before we talk more in depth about how the sense of smell has been discredited, let's talk about how it works in humans. Basically, this sense serves to identify chemicals in the air, which, when they make contact with chemoreceptors in the nose, send a nerve signal to the brain where they are identified.The nose sends a nerve signal to the brain where they are identified as odors.

Inside the human nose there are three nasal turbinates, one for each of the three nostrils. These turbinates are surrounded by the pituitary, a mucosal structure that is responsible for warming the air before it reaches the lungs. The pituitary secretes a mucus, pituitary, which moistens and protects the nasal walls. In the pituitary are the cilia, which contain thousands of olfactory receptors.These cells are responsible for capturing chemicals that enter the nose.

When the chemical substances come into contact with the cilia, a nerve signal is emitted by the receptors located in them. This signal will be sent by means of nerve fibers to the olfactory bulb from which the information will go to different regions of the encephalon where the interpretation of these stimuli will be made and they will be recognized as odors.

Smell and taste are closely related, for this reason when we suffer from a disease in which the nose is affected it also affects our way of tasting food.. This is clear when we have a cold and produce a lot of mucus, fluid that clogs our olfactory receptors that prevent us from detecting odors and flavors, which chemically are the same.

When did this sense begin to be undervalued?

According to John McGrann, who in 2017 conducted research delving into when we began to give little importance to smells, we owe the origins of the myth that smell is an underdeveloped and vestigial sense in humans to Paul Broca himself, a 19th century French brain surgeon and anthropologist. He is credited with spreading the belief that humans have an underdeveloped olfactory system compared to other species.

In his papers dated 1879, Broca, based on the fact that the human olfactory area had a smaller volume compared to the rest of the brain, interpreted this to mean that the human olfactory system was underdeveloped compared to the rest of the brain, interpreted this to mean that humans were not as dependent on olfaction for survival as were other animals, such as dogs and rodents.. Thus, he indicated that this was what made us have free will and that instead of being guided by smells, we made use of our mental capacities, especially our reason.

This statement came to influence great referents of psychology, among them Sigmund Freud, who came to affirm that due to the lack of smell in human beings this made us more prone to mental disorders. This statement is partly right, but it does not apply to the entire human species. What has been seen is that people with impaired or reduced sense of smell are more prone to psychiatric disorders, not because the sense of smell is impaired or reduced.This is not due to the fact that the human species has this "reduced" sense.

These "findings" and interpretations made by Broca and Freud as well as by many other thinkers of the 19th century fed the belief that the sense of smell was not very adaptive and was of little use to the human species. In the Western world there was (and still is) the idea that those who allow themselves to be dominated by smell are letting their animal instinct dominate them, an instinct that is always perceived as something irrational and illogical, thus discrediting this sense even more.

However, modern and cross-cultural scientific evidence disproves that we are bad at detecting smells.. It is true that, compared to other species, our olfactory bulb is a little smaller, but this smallness is rather relative. This brain structure sends signals to other areas of the brain to help identify odors and is actually quite large and similar in size and number of neurons to that of other mammals that no one has questioned are good at recognizing and being guided by odors.

The importance of smell

Smell is important, since it plays an important role in choosing food, avoiding harm and deciding who is our mate. In addition to these more "animalistic" functions, we should add that humans are the only species that use smells for religious (e.g. incense in churches), medicinal (e.g. aromatherapy) and aesthetic (e.g. air fresheners and deodorants) purposes. Smelling seems to be not only an individual act, but an interactional one..

We differ from other animals not because we have it atrophied, but because we put it to a different use. For example, dogs are able to differentiate the odors of different urines for territorial and dominance purposes, an ability that humans have no use for. On the other hand, we are able to differentiate between the smells of wine, cheese or even between varieties of cocoa and coffee, which is a useful skill that we use to recognize which foods suit us better or have a higher caloric and lipid content.

Cross-cultural view

Many studies have tried to deepen the importance of olfaction by analyzing the wide repertoire of vocabulary that languages may have to encode odors.based on the idea that if a concept, feeling or sense is important for the human species, several languages must refer to it. That is, if odors are important to humans, more than one linguistic community must have an extensive repertoire in the form of words and grammatical structures to refer to them.

When this question began to be addressed, many studies focused on English, a language that was found to have a rather small vocabulary related to odors and their properties. This same paucity of odor vocabulary was found in other European languages, which led many to rush to believe that indeed this sense carried little weight in the human species.

Language related to odors is more infrequent in English compared to other perceptual modalities. For example, in this language, words related to vision are 13 times more commonly used than words related to the most common odors. A study that analyzed 40,000 words in this language found that there were about 136 times more words related to vision compared to those related to smell.

However, when analyzing the vocabulary of other languages it was found that what was found in Europe was not at all extrapolable worldwide. There were many languages in which odors were represented in a wide variety of words, and not only that, but there were also languages in which odors and their properties were grammaticalized or used as metaphors.

Each language has a different frequency use and number of words associated with odors, with the languages of Africa, the Amazon and Asia having the most words about this sense. Examples include cha'palaa, ǃxóõ, wanzi, yombe, maniq and jahai to name a few, although languages in which smell is of great importance number up to a thousand.

Many of these languages are spoken by hunter-gatherer communities, which makes sense that they would possess extensive odor-related vocabularies.It makes sense that they would possess extensive scent-related vocabularies. For them, knowing how to recognize, identify, position and orient themselves based on what they find in nature is fundamental to their survival. Knowing what lions smell like, how far away a fruit tree is, or what areas near their home smell like are aspects of their daily routine and therefore odors are as important as any other perceptual modality.

Loss of smell as a sign of disease

Loss of smell can be synonymous with something going wrong in our brain. Yes, it can be due to a problem directly associated with the nose, such as having too much mucus or a sinus infection, but it can also be due to the brain structure that recognizes odors failing due to neurodegenerative disease.

Smell can deteriorate as part of the aging process and may be a warning sign of a possible case of dementia.. If a patient indicates that he or she is sensing that things do not smell like they used to, physicians should become concerned. The sense of smell should not be treated as inferior, since just as a person going blind or deaf is of great concern, the fact that they are losing their sense of smell and taste should also be frightening.

Among the diseases in which loss of smell can be found as a symptom of onset of pathology are memory problems and dementias such as Alzheimer's and Parkinson's disease. Loss of the sense of smell has also been found to predict COVID-19. And even if the patient does not have dementia or any disease, losing the sense of smell can lead to more accidents, such as cooking, burning something and starting a fire, which the patient will realize when it is too late.

In addition, loss of smell has been associated with depression and obesity, health conditions that seemingly do not appearhealth conditions that apparently do not seem to be related to the sense of smell. All these pathologies seem to evidence that yes, the sense of smell is important to humans beyond the "instinctive animal" or vestigial sense and that it is indeed important on a health and social level.

Referencias bibliográficas:

• Majifa, A. (2020). Human Olfaction at the Intersection of Language, Culture, and Biology. Trends in Cognitive Sciences. 0(0) 1-13.
• McGann, J. P. (2017). Poor human olfaction is a 19th-century myth. Science 356(6338), 1-6.