Don’t be sniffy if you smell like a dog

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New research debunks the belief that humans sense of smell compares poorly with that of our canine friends

Dont you wish you could smell as well as a dog? Actually, you probably can. In a paper published in the new issue of Science, neuroscientist John McGann of Rutgers University in New Jersey describes the idea that humans have a poor sense of smell as a 19th-century myth. On the contrary, he writes, humans have excellent olfactory abilities. So why have we been doing our noses down?

Weve never had a high opinion of smell. Ever since Plato pronounced it inferior to the noble senses of sight and hearing, theres been a lingering suspicion that theres something primitive and animal about it. For Charles Darwin, our atrophied sense of smell was a mark of evolutionary advancement beyond our ape ancestors.

An upright posture also meant that we were no longer on a level with one anothers smelly parts. An excessive interest in the anal and genital was, for Sigmund Freud, a sign of arrested development, possibly perversion. With the repression of smell, he said, came repression of uncontrolled sexual impulses and the emergence of civilised behaviour; taking too much pleasure in smell was suspect. Freud noted that only infants didnt seem repelled by the smell of faeces.

Freud believed that smell was part of a tension between our animalistic roots and our rational higher nature, which could be a source of neuroticism and mental disorder, says McGann.

But a scientific disregard of our sense of smell didnt start with Freud or Darwin, McGann says. He puts much of the blame on the 19th-century French physician Paul Broca, an expert on the anatomy of the brain. Broca is mostly remembered now for having identified a region of the brains frontal lobe associated with language processing, which is named after him. He believed that this region was the source of the enlightened intelligence of humans and that its development crowded out the part of the brain that processes smell: the olfactory bulb. In humans, the olfactory bulb is relatively small compared with rodents and most other mammals and is tucked away rather than sticking out at the front of the brain.

Broca viewed smell as an animalistic sense that drove irrational behaviour and thus must be diminished in importance in a rational being with free will, says McGann. He has traced the evolution of that view into a prevailing medical opinion that humans have a poor sense of smell.

Airport
Case closed: sniffer dogs provide a service few people would consider for a career. Photograph: Steve Parsons/PA

But smell scientist and psychologist Avery Gilbert thinks that Broca wasnt so far from the truth in some ways. The repositioning of the human olfactory bulb beneath the frontal lobe, he says, enables us to integrate smell into our other mental processes: not just to sense it and respond automatically, but to think about it. It lets us freely assign different emotional values and meanings to a given odour, indeed to treat a smell as a symbol, he says.

Besides, a relatively smaller olfactory bulb doesnt mean were poor smellers. As McGann shows, the absolute size of the olfactory bulb the total number of neurons it contains is about the same in all mammals, from mice to men. Whats more, sensitivity to smell depends on the odourant: were much better than rats or monkeys at detecting one of the odourants in freshly brewed coffee, for example.

To experts in the science of smell, its not news that were better smellers than popular belief allows. Theres a long history of olfactory specialists arguing that human smell is actually quite good, McGann says. But somehow the myth has persisted anyway, both in the general public and in broader scientific world.

Dogs have some advantages. They have nostrils and scent-sampling behaviours that are more efficient than ours and they devote more of their brain and behaviour to investigating and analysing smells than we do, says Gilbert. But weve also bred them partly for olfactory prowess, especially at a distance. Theyll always smell an elk a hundred yards off before we do.

The sensitivity of a trained tracker dog might be hard for humans to match. Dogs who can follow the smell of a person through field and forest after having smelled a scarf have a sensitivity we can only dream of, says smell expert Luca Turin, author of Perfumes: The A-Z Guide.

Yet on the whole humans compare pretty well, especially for close-up smells, where dogs tend to rub their noses on the source rather than relying on airborne scents. Human smell is not the same and dogs or rodents, but its clearly not notably worse, says McGann. If you restrict testing to traditional, volatile odours, then dogs and humans stack up pretty well against each other.

Similarly, we use sniffer dogs not so much because they are extraordinary smellers but because they can be highly trained. For example, they are currently being used to sniff out molecules produced by cancer cells in human clinical samples. But we could probably do such things too, says McGann. Humans can follow scent trails through a park and medical technologists have been smelling urine samples for diabetes for decades.

As for drug detection, we can probably detect cocaine at levels comparable to dogs, Gilbert says, but few of us are willing to make a career of crawling around airport luggage carousels to find the stuff.

Our belief in our poor sense of smell might be partly self-perpetuating. Discouraged by the myth, and subliminally worried by the Freudian message that enjoying smell is infantile and perverse, we dont develop the habit or the vocabulary. Sommeliers and perfumers do have very developed senses of smell, says McGann, but this often comes about through practice and training on how to label smells that most lay people dont know the words for.

So now you can relax and release your olfactory skills. I can tell you from personal experience, says McGann, that if you put your nose on the ground and smell, you can find a fascinating world of stimuli you never noticed.

Read more: www.theguardian.com

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