The human sense of smell has often been thought of as our species’ Achilles heel, at least when compared to other living creatures. While people are obviously capable of doing a great many things animals cannot do, and have a particularly keen sense of sight, it has long been believed that the trade-off therein has been our rather weak sense of smell. But new research suggests that being able to sniff and smell may not be as weak in our species as we were trained to believe it is.
Earlier this week, Rutgers University neurobiologist John McGann wrote about this long-held misconception — that the human sense of smell is weak because it’s a trade-off for our sharp vision. But it is, in fact, quite sharp, as McGann further clarified in an interview with Vox.
“We’re like lots of mammals with a perfectly good sense of smell, and if we paid more attention to it, I think we’d realize how important it is to us.”
In the new paper published this week in the journal Science, McGann explained how the whole myth had started — people started believing that the human sense of smell wasn’t too good as a result of an incorrect hypothesis from a 19th century scientist. About a century and a half ago, French anatomist Paul Broca concluded that the olfactory bulb, or the part of the brain that processes smell, was small in relation to the human body, as compared to its size relative to animal bodies. This led him to theorize that animals need the sense of smell much more than humans do.
“Through a chain of misunderstandings and exaggerations beginning with Broca himself, this conclusion warped into the modern misapprehension that humans have a poor sense of smell,” wrote McGann.
Indeed, several studies after Broca’s suggested that the human sense of smell is a weak one. And, as The Guardian wrote, it wasn’t just Paul Broca thinking this way in his era or earlier; Charles Darwin himself said that this sense was of “extremely slight service” to civilized people, while Aristotle wrote even further back that “man smells poorly.”
For the past 14 years, John McGann sought to debunk these theories, and in the new paper, he wrote that our sense of smell is similar to that of rodents, dogs, and other mammals. But how did he come up with this radically different conclusion from what Broca and other scientists had come up with in the past?
According to The Guardian, humans have about 1,000 odor receptor genes, which is a similar yet lower count to the 1,100 in mice. But other studies had hinted that the number of odor receptor genes is not a solid indicator of an animal’s ability to smell things. For example, cows have 2,000 olfactory genes, which is a much greater count than that of dogs.
As for humans, it was once thought that about a third of our olfactory genes were functional, with the remaining two-thirds “evolutionary relics” that our ancestors may have used and needed, but serve no purpose to modern humans. Newer research, however, hints that the human sense of smell may use far more genes than what once was thought.
That’s not the only interesting takeaway from McGann’s research. According to the Rutgers scientist, dogs, for instance, have their olfactory receptors more concentrated in their noses than humans do, thus making them more sensitive to the scent of explosives. But humans are more sensitive than dogs to the smell of amyl acetate, which is the agent that gives bananas their distinctive odor. That, said McGann, may be because it was more important for our ancestors to determine if fruit is ripe, but much less important to dogs.
Likewise, there are some other chemical agents that animals can sniff out better than humans can, and vice versa, McGann noted.
Additionally, McGann observed that the human sense of smell gets neglected in other ways, such as many of us not realizing its ability in helping us make decisions, such as whether leftover food is still good to eat or not, or even the rather peculiar tendency to “take a whiff” of another person’s hands after shaking them — McGann calls this an “unexpected olfactory component to (a) common social interaction.”
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