“Les parfums de la nature” by Roland Salesse published by QUAE (2024).

Hello Roland Salesse, you recently wrote the book “Les parfums de la nature”, published by QUAE. The universal chemical communication of living organisms is at the heart of your book. Today you remind us of the importance of the sense of smell, both in nature and in our lives.

How can anyone take an olfactory walk?

A simple walk with our noses to the wind through the twelve months of the year already brings us face to face with the different facets of chemical communication in nature. We come across well-known fragrant plants that flower out of season, brought back to Europe by forgotten explorers. We find trees and arable fields, the scene of a silent – but nonetheless fragrant – balance between living species. And always the presence of man, shaping his environment, in town and country.

How does the sense of smell work?

Our perception of the chemical environment varies from one organism to another. Bacteria, for example, which have only one cell, associate the detection of VOCs (volatile organic compounds) with a simple behaviour, such as approaching or fleeing. Plants, which cannot flee, have a decentralised system: each cell is equipped with receptors for internal or external signals, enabling them to respond appropriately, whether to repel herbivores or attract pollinators. In animals, this process is centralised: peripheral sensors receive chemical messages, which are then converted into nerve messages and transmitted to the brain for analysis and appropriate response.

Why do you say that plants are fantastic chemical factories?

A plant cannot move (it is said to be sessile, from the Latin sessilis, “to sit”). So how can it reproduce, feed itself and protect itself from danger and predators? Chemically! Photosynthesis provides the building blocks and energy for the synthesis of carbohydrates, proteins, nucleic acids and fatty acids. Over the course of evolution, variants of the genes for the enzymes that process these building blocks have accumulated, providing numerous possibilities for transformation into products that protect plants, repel parasites, attract pollinators and parasitoids (parasites of parasites) and communicate with other plants, fungi and bacteria.

Did you say “VOCs”?

VOCs (volatile organic compounds) are not just evolutionary fantasies, they have ecological roles. These volatile molecules are emitted not only into the air but also into the soil. VOCs are always forms of communication; we observe the many tricks that plants use to protect and defend themselves, to reproduce by attracting pollinators with attractive scents and ingenious devices, and finally to feed themselves.

And for animals: do you have to smell to survive?

Essential to the survival of plants, scents are also essential to animals. The sense of smell plays a major, and sometimes essential, role in ensuring the survival of individuals and species. Smells enable us to find our way around the environment, defend ourselves against aggressors, feed ourselves and reproduce. On land and at sea, fish, amphibians, birds, mammals and insects are all affected.

Finally, for humans: what does body odour have to say?

Body odour is linked to the genome, but also to the microbiota that often transforms odourless secretions (such as sweat) into more or less (mal) odorous VOCs. The so-called ‘civilised’ world takes a dim view (or a bad nose!) of these body odours. Yet they provide a great deal of information about us: our age, sex, reproductive status, what we’ve eaten and our state of health. Animals have no such prejudices and sniff each other shamelessly, using body odours for social and sexual purposes.

When did man first add a touch of fragrance?

The history of perfumes dates back to at least the Neolithic period (from 9,000 BC) in the Near East, since containers from this period have been found that had been used for perfumes or ointments. We can now identify the plant or animal species used to prepare them. Perfume craftsmanship has spanned the centuries since antiquity, becoming an industry in the 19th century with the rise of chemistry. Today, artists compete with each other in their imagination to add fragrance to their works and offer the public perfumed performances and installations.

From the ocean to the land, from the subsoil to the upper atmosphere, VOCs are everywhere. But their emissions vary over a fantastic time scale: the circadian rhythm (24 hours) and the annual rhythm (365 days) are sensitive to our nostrils and our eyes. But the current state of chemical communication can only be understood in the light of evolution. Since life first appeared around 3.5 billion years ago, species have only been able to survive and adapt by interacting chemically with their local and global environment. In all biotopes, from the smallest organisms (microbes) to the largest, the rule has been the same: “adapt or disappear”. This is why current climate change is causing some concern because of its unprecedented speed. Will mankind, the cause of this upheaval, be able to spare the planet?

Thank you very much Roland Salesse for this interview, which makes us even more keen to discover your book.