“I say, I say, I say! My dog’s got no nose!”
“How does he smell?”
“Terrible!”
Music Hall joke from the 1930s
Humans versus Dogs
If you have read anything about the human sense of smell, it has probably been compared unfavourably with that of a dog. When you get past the hyperbole (10,000 times better, 100,000 times better) you may find more consistently quoted comparisons. A dog, apparently, has 30 million olfactory receptors where humans have only 6 million. The part of a dog’s brain that processes odours is 40 times larger than that of a human, apparently.
Recent studies have challenged this received wisdom. The idea that a dog’s sense of smell is so superior was first published in 1879, and since then most comparisons have been subject to confirmation bias. CBC recently reported a study by John McGann, of Rutgers University-New Brunswick, which concluded that humans could track scents well. It concluded that: “It can be said that we are as good as, but not the same as, our canine companions”.
McGann’s study engaged 32 human volunteers to track a scent whilst blindfolded and wearing earmuffs, thick gloves and padded kneepads to limit input from other senses. The volunteers tracked the scent across the ground while on all fours. Two thirds of them “did pretty well”.
Why we smell
Most animals rely on a sense of smell to:
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- Detect danger
- Find water
- Find food
- Find a mate
- Determine if a potential mate or rival is in season.
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Humans are still equipped with a sense of smell capable of all these things. It’s just that at some point in our evolution we started walking upright. Our noses were no longer close to the ground to find water or food, and they weren’t on the same level as our genitals to guide us to a suitable mate. We came to rely on sight as our primary sense and disregarded smell. Now, if somebody is physically incapable of detecting and identifying smells, we don’t even consider it a disability.
Our sense of smell begins to develop in the womb. Immediately after birth it is our most developed sense, guiding us to food. As adults, our sense of smell is usually more reliable than a “sell by date” as a means of determining whether food is fit for consumption.
As we develop, our sense of smell can still warn of danger (for example by smelling gas, or smelling fire). The expression “something smells” is used in connection with situations that don’t feel right, for example when we suspect a scam.
Most women have a better sense of smell than most men. The sensitivity of a woman’s sense of smell varies during her menstrual cycle. A few people, male and female, have a much more acute sense than the majority. Some have little to no sense of smell at all. Although women generally have a superior sense of smell, many perfumiers, “the noses”, are men.
How we smell
Our senses of smell and taste are closely linked, and the brain processes them in similar ways. Our other senses pass through a section of the brain called the thalamus. The thalamus operates as a filter, reducing the level of “noise” that would otherwise disrupt our conscious thoughts. Our sense of smell bypasses the thalamus. If we detect a new smell, we know about it at once. More than that, a new smell is instantly linked to our memories. Anything we already know about it is immediately recalled. Smell is our most visceral sense, able to affect our emotions directly.
There is a strong link between smells and memory. Although we are not aware of the background smells in our home, the distinctive collection of smells is imprinted on our memory. If we leave home for a while, we become used to different smells as a background. On our return we are briefly aware of the characteristic smell of our home. If you visited a grandmother’s home as a child, you probably remember its distinctive smells.
Loss of sense of smell can be an early indicator of the onset of Alzheimer’s disease.
Smelling Good
Smell has a significant role in our selection of a mate, and how we engage them. Both our natural body odours and perfume play parts in this process. In the seventeenth century a woman might peel an apple and hold it under her armpit before sending it to a lover or prospective lover. In modern western society, body odours are masked with deodorants which contain synthetic scents. Although these synthetics can mask natural body odours to our conscious mind, the odours are still present. We perceive them unconsciously and they affect our emotional responses.
Overload
We filter out smells that we have been experiencing for a while. We are not aware of background smells, only new ones as they appear. New smells may indicate danger, so grab our attention until we have identified them. We are not interested in persistent background smells. That’s how we perceive stinky people but stinky people can live with themselves.
The ability to filter out persistent smells can be unhelpful for people who use their sense of smell constantly. Perfumiers, sommeliers and people who taste tea or coffee to assess its quality need to keep their sense of smell engaged. One method of refreshing a sense of smell is to inhale through woollen fabric, the sheepier smelling the better.
It’s time to smell the coffee…