19
Mar

Climate shaped the human nose, researchers say

Variations in nose shape developed as a result of natural selection in response to different climates, new study suggests

Human noses have been shaped by climate, according to research probing variation in the human snout.

Researchers say their findings back up the theory that wider nostrils developed in populations living in warm, humid conditions, while populations living in high latitudes, such as northern Europe, developed narrower nostrils as an adaptation to the chilly, dry conditions.

People have thought for a long time the difference in nose shape among humans across the world may have arisen as a result of natural selection because of climate, said Arslan Zaidi, co-author of the study from Pennsylvania State University. But while previous studies were based on measurements from human skulls, he says, the new study looked at nose shape itself.

Writing in the journal Plos Genetics, researchers from the US, Ireland and Belgium describe how they began to unpick variations in nose shape by using 3D facial imaging to take a host of measurements from 476 volunteers of south Asian, east Asian, west African and northern European ancestry.

The results revealed that only two out of seven nose-related traits were found to differ more between the populations than would be expected from the impact of random, chance changes in genetic makeup over time. The authors say that suggests variations in those traits have been influenced by natural selection.

With further analysis, based on data from participants of west African and European ancestry, confirming that nose shape is highly heritable, the team looked to see if there was a link between nose shape and climate.

Blue
Blue boxes represent alleles for narrower nares while red boxes represent alleles for wider nares. Colours in between represent intermediate phenotypes. The colour scale represents climatic variation in temperature and humidity, to show that narrower nares are favoured in cool-dry climates while wider nares are favoured in hot-humid climates. Photograph: Arslan A. Zaidi and colleagues

To do so, they examined nose measurements from a total of 140 women who were of west African, east Asian, northern European or south Asian ancestry, and whose parents lived in a region that matched this ancestry. The birth locations of each participants parents were then used to assign to each woman temperature and humidity values that approximately reflected the climate experienced by their recent ancestors.

The results showed that nostril width is linked to temperature and absolute humidity, with participants whose ancestors lived in warm-humid climates on average having wider nostrils than those whose ancestors lived in cool-dry climates.

That, says Zaidi, could be because narrower nasal passages help to increase the moisture content of air and warm it a bonus for those in higher latitudes. Cold and dry air is not good for our internal airways, said Zaidi. But, he adds, There is no universally good or better shape your ancestors were adapted to the environments in which they lived.

Zaidi acknowledges that the study does not rule out the possibility that factors other than climate could be at play, not least that different populations might consider certain traits more or less attractive, meaning that sexual selection could also be behind the differences.

Zaidi believes unpicking human adaptations is valuable in understanding disease risk. As we become more of a global community, as we move around the world, we are going to be encountering climates that we are not adapted to he said, suggesting that moving to a very different climate might increase the risk of respiratory disease. But, he added, This may not be necessarily true for various reasons such as of modern medicine and the fact that our current climate is very different from what it used to be.

Noreen von Cramon-Taubadel, from the University at Buffalo, New York, who was not involved in the study, said climate pressures were unlikely to be the full story when it came to possible nose adaptations.

Although nasal width may be subject to natural selection, it is not clear that this is being driven by climate, she says pointing out that the studys link between climate and nose shape disappears when northern Europeans are removed from the analysis.

Whats more, says Von Cramon-Taubadel, the study focuses only on the external features of the nose even though its internal structure is also important when it comes to air-conditioning. So while this study sheds light on the evolution of external nose shape, it does not necessarily address the aspects of nasal anatomy that are most important for understanding climatic adaptation, she said.

Zaidi said that further research is necessary to test the link between climate and nose shape, including carrying out similar studies with participants from a wider range of ancestries, including native Americans and Inuits, and unpicking the genes that underpin differences in nose shape.

But, he adds, the current study highlights an important point.

There are more similarities among humans from different populations than there are differences, said Zaidi. This is something that we are finding in our paper as well most traits in fact dont differ greatly between populations.

Read more: https://www.theguardian.com/science/2017/mar/16/climate-shaped-the-human-nose-researchers-say

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