Every day we come into contact with hundreds of aromas. However, there are some that we like more than others. In fact, many people share a taste for the smell of a new book, as well as the smell of freshly baked bread and the smell of wet earth. However, have you ever wondered why almost all of us like the smell of wet earth, the smell of rain? Is it a cultural issue or perhaps something that has been passed down to us by our most remote ancestors?
Smells: A connection to the deepest part of the brain
Smells trigger an almost instant brain connection with emotions. Our olfactory bulb has direct connections with the limbic system and the amygdala, areas linked to the processing and modulation of emotional states. In fact, studies using functional magnetic resonance imaging have shown that familiar smells (both those that trigger positive and negative memories) immediately activate the oldest structures in our brain.
Neuroscientists believe that this special connection may have its roots in our distant past. At that time, smell must have been a very important sense for our ancestors, just as it is for most animals today. Smell could warn them of danger, so it was essential that it triggered a rapid response that could save their lives in a matter of seconds. It is therefore not surprising that scents trigger an almost instantaneous and particularly intense emotional reaction.
Obviously, since we are not only programmed to avoid risks but also to seek pleasure, this same connection is created with aromas that have been linked to positive experiences, such as the smell of wet earth or rain.
Two smells, one meaning
The smell of wet earth and rain is composed of two aromas that are quite easy to differentiate: petrichor, which is fresher, sweeter and softer and emanates mainly from stones, and geosmin, which is stronger, with a musty vapor and comes from plants and wet earth.
Scientists believe that our taste for the smell of wet earth is an inheritance from our ancestors, for whom rain has always been a source of life and synonymous with survival. Petrichor , a term coined in 1964 by two Australian scientists studying the smell of rain, is released when raindrops hit rocks. At that moment, a series of oils from plants are released, which they had been accumulating during the period of drought.
According to anthropologists, our ancestors established a strong positive connection with this smell, which indicated to them that the dangerous period of drought had ended and the rain had begun, which would revive the plants and increase their chances of survival.
On the other hand, geosmin is a molecule produced by the bacteria actinomycetes, which grows in moist soils and helps to decompose organic matter and contribute to the formation of humus. When there is drought, this bacteria releases its spores in order to survive (this process is known as the dormant stage and is a defense mechanism against desiccation). However, when it rains, these spores spread through the air and remain suspended in the environment, generating that smell of wet earth, which has a slight musty vapor.
Some studies have shown that the smell of geosmin is what guides some animals to find water in the desert, and it is also known that humans are particularly sensitive to this molecule. Therefore, once again the hypothesis that we are attracted to the smell of wet earth is confirmed because for our ancestors it was synonymous with life and food.
Obviously, when a person has lived a negative or traumatic experience and has associated it with this aroma, it immediately stops being pleasant since our brain classifies it within the potentially dangerous aromas that we should avoid.
References:
Bentley, S. D. et. Al. (2002) Complete genome sequence of the model actinomyceteStreptomyces coelicolor A3(2). Nature; 417: 141-147.
Bear, I. J. & Thomas, R. G. (1965) Petrichor and plant growth. Nature; 207(5005):1415-1416.
Bear, I. J. & Thomas, R. G. (1964) Nature of the agrillaceous odor. Nature; 201(4923):993-995.
