Hot, Humid Weather May Have Helped Shape Human Noses

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Noses may be the unsung heroes of the face. We tend to think of them as mere scent collectors, but noses do so much more, including make it possible for humans to survive in different climates all over the world. A study published in the American Journal of Physical Anthropology explores how that may have come about.

Your nose acts like a portable, personal HVAC system, treating the air you inhale to make it easier for your body to process. In the winter, your nose warms the air so that it’s nice and toasty by the time it reaches your lungs. In arid climates, our noses add humidity to our inhalations to keep our respiratory tracts from drying out.

Human nose shape, like skin color, generally varies by latitude. Scientists have suggested that northern Europeans’ thin, pointy noses evolved to help their ancestors process their homelands’ cold, dry air, since narrow nasal passages mean that a greater percentage of inhaled air has to come into contact with heat- and moisture-adding mucous membranes. This, the researchers believed, was the only way the nose has evolved: away from the flatter, wider noses of people living closer to the Equator. The air in those regions is typically hot and humid already, requiring no special treatment. So if the winter nose is a custom job, they said, the summer nose must be the base model.

But "we don't really think that that's true," said biological anthropologist Scott Maddux of the University of North Texas Health Science Center. Maddux and his team used global climate data from 1901 to 2013 to construct maps of average annual temperature and humidity. Then, they compared those with the results of a study from 1923, which measured the noses of more than 15,000 people from 147 countries.

Their results suggest that, rather than a starting point, wider, flatter noses have themselves evolved to help their owners cope in those hot, muggy climates. Humidity is rough on the human body. It makes it much harder for us to shed heat by sweating, so we have to find other ways to cope. One way to do that might be allowing more heat to escape through the two holes in the middle of our face. The wider the nose, the more heat it can funnel out of the body.

More questions remain. Nearly all the work our noses do takes place inside in a part called the nasal cavity. If it’s the cavity that’s doing the heating and humidifying, Maddux says, why would the outside of our noses need to change at all? To find out, scientists will need to go deeper inside, all the way to our skulls.

Nicholas Holton, a biological anthropologist at the University of Iowa, was not involved in the study but praised the team’s work. "A big part of any face, not just the human face, is the nose," he told Inside Science. "Literally, it's a central component of the skull, so understanding what's happening with the nose may tell us a lot about what's happening with the rest of the face."

[h/t Inside Science]

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