Can Human Beings Actually ‘Smell’ Fear? A New Book Says Yes

A new book titled ‘On the Scent: Unlocking the Mysteries of Smell and How its Loss Can Change Your World’ by Paola Totaro and Robert Wainwright suggests that human beings can actually ‘smell’ fear.

While most olfactory scientists are students of the human brain, nose and smell-driven behaviours, Professor Jonathan Williams, an atmospheric chemist at the Max Planck Institute in Germany, studies air. The connection between atmospheric chemistry and the sense of smell may seem a little indirect and deserves explanation: when odour molecules are released into the air, let’s say from a fruit ripening on a vine, the initial concentration of the smell diminishes over time and fades away with distance from the source. This is not just because odour molecules become diluted into the surrounding air but also because sunlight breaks them down in a process known as photo-oxidation.

Human noses don’t detect all smells equally. The ones we are most sensitive to are compounds found in nature. Some of these can be detected at extremely low concentration while others we barely perceive at all. Williams and his colleague Akima Ringsdorf told the Royal Society that they now think they know why. They compared the contents of a smell sensitivity database, compiled over more than a decade by Japanese scientists, with an atmospheric chemistry database. This meant they could compare the smell thresholds with the lifespan of an array of organic molecules in the air. Their findings revealed a striking link between chemical families such as alcohols and esters associated with some foods, particularly fruits, and nitrogen and sulphur compounds associated with fire and bodily wastes.

Evolution and adaptation, they suggest, has led us to become most responsive to the chemicals that react most quickly with other elements in the air and then disintegrate and disappear just as quickly from our noses. These are specialised olfactory sensitivities that help us find – and quickly identify – danger or toxic substances.

Williams told colleagues at the Royal Society conference:

A good sense of smell is a big advantage when looking for food. If you want to find a nutritious ripe fruit in a dense, dark forest you need to be able to follow a smell gradient as it twists and turns in turbulent air streams. And the molecules with the shortest lifetimes have the steepest gradients. The results we have seem to support the general hypothesis that there is a link between atmospheric chemistry and the sense of smell, which nobody had thought of before.  

Williams came into the field of human smell by accident. He has spent more than two decades researching how gases emitted into the Earth’s atmosphere contribute to climate change and embarks on a twice-yearly odyssey involving large and small aircraft, cars and a final climb on foot to work in a 325-metre-high research tower built deep in the Amazon by his institute. Here, he and his research assistants and students use a suite of sensitive instruments to measure how specific gases emitted into the air by vegetation (volatile organic compounds) react in the air and contribute to the production of ozone and other particles.

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In 2016, a member of his student group, driven by sheer curiosity, decided to blow into one of the highly sensitive instruments designed to capture the fresh forest air and, to the team’s surprise, the breath sample was found to contain a similar array of the substances released by Amazonian jungle plants, including lots of isoprene, one of its major constituents. This raised the question: could it be that we humans, all 7.5 billion of us, are contributing to climate change?

A new paper titled ‘Cytoelectric Coupling’ by researchers at MIT, City University of London, and Johns Hopkins University is a groundbreaking hypothesis on how our brains function.

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