“Man smells poorly,” Aristotle wrote, while Charles Darwin concluded that a sense of smell was of “extremely slight service” to the civilised human. When it comes to detecting odours, we have long dismissed human abilities as second-rate.

Now this view has been challenged in a scientific analysis that argues the human sense of smell has not only been underestimated, but that it may rival that of dogs and rodents.

John McGann, a neuroscientist at Rutgers University in New Jersey and the paper’s author, reached this unexpected conclusion after spending 14 years studying the olfactory system.

“For so long people failed to stop and question this claim, even people who study the sense of smell for a living,” he said. “The fact is the sense of smell is just as good in humans as in other mammals, like rodents and dogs.”

McGann said he was alerted to the “big myth” after trying to translate rodent experiments to humans.

“We’d have two odours that mice couldn’t tell apart, expecting humans wouldn’t be able to, and they’d be like ‘that’s one and that’s two’,” he said. “It was amazing how good the human olfactory system was.”

McGann identifies a 19th century brain surgeon, Paul Broca, as the primary culprit for introducing the notion of inferior human olfaction into the scientific literature.

Broca noted that the olfactory bulb – the brain region that processes odour detection – is smaller, relative to total brain volume, in people compared with dogs or rats. The discovery inspired Freud’s belief that human sexual repression may be linked to our “usually atrophied” sense of smell.

In the latest paper, published in Science, McGann points out that in absolute terms the human olfactory bulb is bigger than in many mammals and a literature search revealed that the absolute number olfactory neurons is remarkably consistent across mammals. “We went to the medical school and looked at a human brain,” he said. “We put the human bulb next to the mouse bulb and gasped. It was gigantic.”

McGann goes on to deconstruct other metrics that have been used to support the idea that human smelling abilities are limited.

Humans have approximately 1,000 odour receptor genes, for instance, compared to 1,100 in mice, which some had taken as confirmation of mouse superiority. However, other work suggests there is not a tight relationship between the number of olfactory genes and smelling ability. One study found that cows have 2,000 such genes - far more than dogs.

The genes code for different “flavours” of odour receptor in the nose, attuned to selectively detect different volatile chemicals in the air. Initially only about one third of human olfactory genes were thought to be functional and the rest appeared to be evolutionary relics. However, recent research suggests the number could be far higher.

Even the constant sniffing of some animals may also be misleading, McGann said. When a rat is exposed to a new smell, for instance, it performs “fast investigative sniffing” but rats have the same reaction to hearing an unfamiliar new sound or seeing something unexpected. “Sniffing, to some extent, means ‘I’m curious’,” he said.

McGann concedes that dogs, at least, have a higher concentration of olfactory receptors in their noses than humans and this probably explains their lower threshold for certain smells such as explosives.

However, even dogs have weak points. Humans are more sensitive than dogs to amyl acetate, the main odorant in bananas, for instance, presumably because identifying ripe fruit was more important to our own ancestors and irrelevant to those of dogs.

The review is not the first scientific paper to suggest human olfactory abilities have been underestimated. A study published last year found that humans are able to distinguish between one trillion different smells (although the validity of this claim has been disputed) and an earlier study showed that people are, surprisingly, able to track a scent across a grassy field.



McGann said that he has tested out the tracking finding and found it compelling. “I have got down on my hands and knees in the park to track stuff,” he said. “Try it in your yard, it’s really quite impressive.”

Matthew Cobb, professor of zoology at Manchester University, said the review had altered his own perspective on a study that he has focused on for much of his career. “We have this myth that humans can’t smell very much,” he said. “McGann’s exploring the actual evidence for that, which it turns out is fairly poor. It’s going to change my teaching next year.”



Others were more sceptical. Alexandra Horowitz, a scientist at Barnard College in New York, whose work focusses on canine olfaction, notes that while dogs track scents, find drugs and detect ovarian cancer in plasma samples, humans merely “notice if there is a bad smell on the train or someone has been cooking when we come home.”

“That there are olfactory specialists, such as perfumers or animal trackers indicates that with attention, we can get much better,” she added. “But not dog-level.”