Minnesota winters are dreadful for me. It’s fun to play in the snow, and shoveling is a good workout, but my nose is constantly running and I’ve got a perennial case of the sniffles every November through April.
Perhaps I have the wrong nose shape for where I live.
Some people have larger noses, or thinner noses, or wider noses. The right nose shape might be an important part of thriving in cold or dry conditions.
Nose shapes and sizes vary dramatically among humans. These variations may be due to the climates where our ancestors lived. This idea is called Thomson’s Nose Rule, coined in 1923 by anatomist Arthur Thomson.
More recent research backs this up, showing that nose sizes in different populations of people correlate with the climates where those populations live — and that nose shapes are changing more than we’d expect from random selection alone.
What the nose really knows (and does)
Noses aren’t just for smell. They’re the first stop for air coming into our lungs, and they carry out two important functions to modify that air: warming and humidifying.
The inner passages of our lungs contain mucus, which helps trap any dust and germs in the air we inhale. That mucus is constantly being swept out of our lungs, to be replaced with new, fresh mucus. But if the air that we breathe in is too cold or dry, the old mucus dries out and becomes harder for us to clear away.
As we inhale, blood vessels in our nose help to warm the air by bringing warm blood close to the surface of the skin. The mucus (mmm, snot) in our nose releases its water to make our inhaled breath more humid.
The result? Cool, dry outside air becomes warm and humid by the time it reaches our lungs. That keeps our lungs operating smoothly, most of the time. (If you take multiple deep breaths on a cold day, you may dry out your lung mucus and feel a burning sensation in your chest as your lungs protest.)
But not all noses are equally efficient. This is where climate may have influenced our evolution.
Less sun, longer nose
For a nose, heating and humidifying is all about maximizing the internal surface area. The more surface area versus total air volume, the more heat and humidity can be injected into the air.
In one study, researchers measured the width of nostrils and of the base of the nose, and compared them with local temperatures and humidity for different populations. They found that some aspects of the nose, like nostril width, were linked with climate. In warmer and more humid areas, the nostrils were wider, since there wasn’t as much need for the body to warm and humidify incoming air.
Overall, as humans moved further from the equator, noses grew longer and thinner, the thinking goes. In times before modern heating, people with thinner noses probably had fewer sniffles in the far north or south, and may have been more likely to reproduce and pass on their genes.
Unfortunately, our technological advancements, like air conditioning systems, have outpaced evolution.
Are some nose shapes… sexy?
Evolution is tricky to study, because there’s rarely a single reason for any feature or trait appearing. Evolution is a grab bag of random assortment and multiple selective pressures. It’s like having a hundred people all pushing around a giant ball; the ball will roll, but its end course is difficult to map to any one particular person’s push.
In the case of noses, there’s certainly other factors at play besides the relative outdoor temperature and humidity.
Sexual selection, for instance. Many people have strong opinions on what makes a nose attractive, although top Google results for “what makes a nose attractive” are all from plastic surgery websites, which feels biased. In different cultures and regions, a certain style of nose may help a person land a mate — and what’s attractive in one group or culture may not be as sexy in another.
Evolution never has an “end goal” in mind. It’s just trying out new ideas through variations in our DNA. Those that work best for that particular creature are more likely to be passed on to its offspring, going from ‘random DNA mutation’ to ‘species-wide feature.’
Humans also exhibit some level of sexual dimorphism for noses; men tend to have larger noses than women. This doesn’t mean men are better at breathing; men also have larger brains by mass, but that doesn’t make them smarter.
Nose shape and size may also be influenced by mate selection; some people may be put off by an especially large nose, while others find it strangely attractive!
All of these factors are likely linked together to some degree. A prospective partner may find a person more attractive if they don’t have the sniffles every winter, or if they can breathe easily in hot, muggy weather.
Thankfully, nose size is not based on how much we lied as a child. It’s genetic, and likely influenced at least in part by the climate where our ancestors lived.
Longer noses aren’t the only possible solution for cold, dry air. Baboons also evolved for the dry, dusty African savanna, but they grew snouts (which also gave them the mouth space to chew tough foods). One creature may evolve a longer nose. Another might develop narrower nostrils, or extra-wet snot that keeps their noses nice and wet.
Perhaps, if global climate change continues to warm the planet, our descendants’ noses will evolve to become wider again.