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Researchers Say You Can Blame Climate For The Shape of Your Nose

You can breathe easy now.

MIKE MCRAE
20 MAR 2017
 

Noses come in all shapes and sizes, from regal aquiline sniffers, to broad snoots and petite beaks.

New research has now linked the width of your nostrils to the climate our ancestors had to deal with, finding the shape of your nose is the result of evolution selecting the right sized bill to breathe in air that's either cold and dry, or warm and humid.

 

Although nose shapes are easy to distinguish in the animal kingdom, the unique size and width of these features among the great apes - including humans - hasn't been all that clear.

Previous hypotheses have suggested that they condition the air's temperature and moisture content as it passes through our lungs.

But one 2016 study disagreed, finding that our nasal cavity did a poor job of adjusting these characteristics, therefore our unusual nose shape was probably a random feature caused by changes to the rest of the human face.

An international team of anthropologists has now weighed in with an analysis comparing features such as the distance between the nostrils and conditions of the atmosphere including temperature, relative humidity, and absolute humidity.

While similar studies have been done so before, this is the first time the faces of living humans have been measured to investigate if there is a relationship between the climate we adapted to, and the shape of our nose.

"Many people have tested the question with measurements of the skull, but no one had done measurements on live people," said researcher Mark Shriver from Pennsylvania State University.

 

It's possible that the variety we see in the sizes and shapes of noses could simply be the cause of genetic drift – the change in frequency of certain genes in small groups due to random deaths and migrations.

So the researchers scanned the faces of 476 volunteers who reported themselves to be from four geographical locations; West Africa, East Asia, South Asia, and Northern Europe.

Using the resulting 3D digital models, they measured the variations of characteristics such as the protrusion of the nasal tip, the base width of the fleshy part of the nostrils called the alar, and the width of the nostrils themselves, and applied a statistical test to determine the likelihood of genetic drift for each feature.

This left just two traits that seem to have been shaped by natural selection between the populations – the width of the alar, and the nares.

Features such as the height of the nose might have evolved under selective pressures within each population, but they didn't separate as groups of people moved around the globe.

Next, the researchers noted the birth locations of the parents of 140 women in the study and assigned the volunteers a value based on the region's climate conditions, specifically its temperature and humidity.

They found that the width of their nostrils correlated strongly with the location's average temperature and absolute humidity, which is the total amount of water vapour in the air without taking the temperature into account.

Basically, wider noses became more common in warm, humid areas, while narrower noses became more prevalent in colder, drier climates.

"It all goes back to Thompson's Rule," said Shriver, referring to the British anatomist Arthur Thompson.

"In the late 1800s, he said that long and thin noses occurred in dry, cold areas, while short and wide noses occurred in hot, humid areas."

No doubt this won't be the last we'll hear on the question of why modern humans and their ancestors have such odd noses, but having fresh data detailing the diverse shapes of our faces adds a lot to the discussion.

It's also likely that there are pressures other than climate that contributed to building our noses.

In the future, the researchers hope to include populations from a wider variety of ancestries, including those native to North America, in the hope of eventually identifying the underlying genes responsible.

For all of our differences, however, the study shows when it comes to the human nose, we all have far more in common than our differences.

This research was published in PLOS Genetics.

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