Nose shape dependent on ancestral climate

19 March 2017

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They’re one of the most distinctive features on a person's face, and noses comes in all sorts of shapes and sizes. Looking at the shapes of noses from populations across the globe and comparing them to the associated climates of those regions, researchers have observed a curious relationship between the two.

From the noses of West Africans, South Asians, East Asians, and Northern Europeans, they found populations associated with colder climates tended to have narrower noses than those from warmer climates, even when accounting for the otherwise random nature of their shape.

Study lead author Arslan Zaidi, from Pennsylvania State University, says that this is evidence for how environmental pressures affect our genetic adaptation in subtle ways that are still having implications for our health today.

The original idea that nose shape could be influenced by climate came from Arthur Thompson in the late 1800’s. He suggested that cold, dry climates favoured narrower noses. Warm, humid climates, on the other hand, favour short, wide noses, he speculated. The idea had been investigated previously by looking at skull shapes, but, by 3D imaging live participants, in the new study, published in PLoS Genetics, the researchers were able to capture various aspects of nose shape for the first time.

What emerged was that, despite the overall variety of nose shapes, the data bore out Thompson’s conclusion. The width of the nose was found to be correlated with the temperature and humidity of the region inhabited by each study population.

According to Zaidi, this makes sense given that noses are the first line of defence against air entering the body as we breathe.

“The lungs are very exposed. The air coming into your lungs carries cold, dryness, bacteria, pathogens and particles. The internal respiratory tracts lining the nose have mechanisms which capture particles and pathogens and warm and humidify the air that’s coming in before it reaches the lungs. Colder air is less efficient for retaining moisture, which turns out to be important for trapping those [substances] that if not captured earlier on, could lead to respiratory diseases.”

This mechanism, Zaidi speculates, could be responsible for the evolutionary pressure that drove the differences in nose shapes with climate. Although nose shape might seem like a trivial example of genetic adaptation to the environment, other more prominent examples can play a big role in health today. Skin colour and pigmentation, serves as another example of an inherited trait that reflects selective pressures on our ancestors to adapt to their particular climate.

Early dark skinned individuals evolved with higher amounts of pigmentation in regions close to the equator, since they were exposed to higher amounts of harmful UV radiation from the sun. Meanwhile those populations closer to the Earth’s poles developed lighter skin with less pigmentation to allow more sunlight to be absorbed for the production of vitamin D.

Zaidi says that, as the world’s population becomes more globalised and populations migrate on extremely short timescales, our inherited adaptations may serve to hinder rather than help. For example, dark skinned individuals living at higher latitudes may require vitamin D supplements to compensate for their mal-adaptation to environments lacking in plentiful sunlight. Whether it’s nose shapes or skin colour, Zaidi says studying how these adaptations emerged gives us new ways to understand and treat such health problems as they arise today.

But, despite those differences, Zaidi says what's remarkable is how similar we all are, rather than how different.

"Most of the genetic and phenotypic variation among humans exists within populations, not among them. This is a well-studied fact. Traits such as skin pigmentation and nose width have evolved faster than most other traits likely due to natural selection because of exposure to the environment. They are an exception rather than the rule. This is important to mention because often people focus on differences and ignore the similarities. I think stories such as ours need to state these caveats to keep reminding people that the facts about human variation do not agree with notions of race."

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