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Making sense of smell: What are pheromones?

Smell that?

Probably not. It’s surprising how quickly we get used to smells. When you first walk into a room you might notice its scent, but after a couple of minutes - sometimes even seconds - your nose adapts.

The sense of smell has a bad rep - for centuries scientists and philosophers have thrown shade at all things olfactory - that’s a posh word for smell. Darwin even considered it the least important sense. But smells play a massive part in our everyday lives, even if we don’t notice them, and can affect the emotions in a way sight, touch, taste and hearing never could.

So what is it about the sense of smell that makes it so powerful? Smell is the least understood sense, and it’s been puzzling scientists for years. There’s hundreds of theories and ideas, but what’s the truth? It’s time to make sense of the most emotive sense we lay claim to.

 

What do pheromones mean?

The emotional power that scent holds is astounding - a whiff of a certain fragrance can transport you to a specific time and place in seconds, which is why it’s easy to come to the conclusion that there’s more going on than just a bunch of nice smells. Some animals communicate using chemical compounds called pheromones, do they have anything to do with why humans are so gripped by smell?

Imagine if all you had to do to grab the attention of that special someone was to raise an armpit? If, from across a room you could snare a potential love-match with the smell of your breathe? It’d make stuff simpler, right? For that reason, pheromones are a hot topic, which often gets complicated with gimmicky fragrances and events claiming to help you ‘find the one’. Although it might seem like a fantasy, communicating with scent is the norm for most mammals. And, as fellow mammals, it makes sense to think that perhaps humans do too.

Pheromones are chemical compounds that allow animals to signal their presence to a mate, navigate dense jungles or mark their territory. They are a means of chemical communication used by living creatures - from algae to elephants - to determine vital information about their surroundings.

Bees and wasps are some of the most fascinating users of pheromones, emitting them to protect themselves, help set up their hives, as well as to facilitate mating. In fact, the yellow jacket wasp uses an alert pheromone to mobilise other wasps when its shell is broken or it’s faced with a threat. In fact, they use pheromones in much the same way humans use Whatsapp to gather people together in the same place.

 

Michael Stoddart, a biologist and zoologist who has spent decades studying the way the animal kingdom interacts with smell, explains: “A pheromone will always have the same effect on the target individual, in exactly the manner that hormones always bring about a specific effect - it doesn’t matter whether you are male or female, young or old, the hormone adrenaline will always get your heart racing.”

However, this is not the case for humans smelling pheromones. Although scents can change our behaviours or actions, they do not do so across the board. Unlike animals we don’t chemically react to smells. When a group of humans smells a rose, for example, there are hundreds of possible physiological and psychological reactions. In other words, humans are not programmed to react uniformly to scent.

What’s more, some pheromones are picked up by a specialised organ called the vomeronasal organ (VNO) - a part of the mouth and nose that allows mammals to taste the pheromones they breathe in.

Michael explains: “The problem for humans is that there is no unequivocal evidence that a VNO exists at all. A trace of a VNO is present in the human foetus, but it degenerates long before birth.

“The gene responsible for the VNO was fatally mutated in our ancestors sometime between 22 and 16 million years ago. So for that enormous length of time pheromones have played no part in the reproduction of human ancestors.”

Michael, and indeed science, seems to say that pheromones don’t have any effect, or possibly even exist, in humans. In fact, to most people animal pheromones smell bad - like pigsties and toilets. Nevertheless, there’s no denying smell plays a role in the way we live our lives - and it has done for millions of years.

 

The oldest sense

Michael explains: “Life has been on Earth for some billions of years, but it would hardly be recognisable to us today. Life in the early days was single-celled and consisted of primitive bacteria-like organisms.

“Individual proto-bacteria could detect the presence of food, or noxious substances in the water around them, and turn away. The fascinating thing is that the biochemical mechanism enabling them to detect chemicals in the outside world is exactly the same as the mechanism we use today to smell a blocked drain or a beautiful perfume.”

So, the way we receive smell hasn’t changed in billions of years, but the way in which we use it has. While we still use our noses to detect danger and keep us safe - by smelling smoke or unhygienic spaces - we do not need to use scents to mate, to defend ourselves, or to navigate the world.

Michael explains that the way humans have evolved, means we are not “slaves” to scent like other species. We do not have instinctive or uncontrollable reactions when we smell a certain note in the air, and have evolved to gather information from a wide array of sources; freeing us up to use scent for pleasure, as well as the tricky business of staying alive.

But that still doesn’t explain why a smell can evoke such strong emotions in humans. Why can one smell make us happy, and another nostalgic? Rudyard Kipling in his poem Lichtenberg proposes that “smells are surer than sounds or sights to make your heart-strings crack,” and most people are inclined to agree.

Michael says this grip on our emotions is probably a result of how primitive the sense of smell is. Because even when we were single cell organisms we were able to smell, the sense is wired differently to our brains than the other, younger, senses.

He explains: “The olfactory receptor cells under the bridge of the nose are connected directly to the part of the brain that controls emotion.

“There are only three neurons from the nose to the brain, unlike in the eye where there are many more. That short, direct route is a consequence of the evolutionary antiquity of smell. The eye and ear report not to the emotional part of the brain but to so-called higher centres.

“When you smell a rose the signal goes first to your emotional brain and only secondarily to the rational brain. If you are a rose expert and want to identify the species from its smell, the emotional brain cannot do this; only when the signal is sent out to the cerebral hemisphere can you sort out which species it is.”

 

Perfume and passion

So, what’s the link between perfume and our brains? The fragrance industry is founded on the idea that a scent can make you alluring to others, is it all built on a lie?

Quite simply, no. While human pheromones probably don’t exist that doesn’t mean they can’t affect our behaviors. Their tight grip on our emotions means that psychologically they could have an impact, even if physiologically they don’t. It’s just that the link is associative rather than chemical. This means that “someone finds a particular scent attractive by association with someone and something that happened in the past,” rather than because there is a chemical driver forcing them to do so, which in a way is a little more romantic.

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