What your nose shape might tell you

March 19, 2017 – The evolutionary reasons for variation in nose shape across human populations have been subject to continuing debate. An import function of the nose and nasal cavity is to condition inspired air before it reaches the lower respiratory tract. For this reason, it is thought the observed differences in nose shape among populations are not simply the result of genetic drift, but may be adaptations to climate. To address the question of whether local adaptation to climate is responsible for nose shape divergence across populations, Qst–Fst comparisons were used to show that nares width and alar base width are more differentiated across populations than expected under genetic drift alone. To test whether this differentiation was due to climate adaptation, the spatial distribution of these variables was compared with the global distribution of temperature, absolute humidity, and relative humidity. Apparently, the width of the nares is correlated with temperature and absolute humidity, but not with relative humidity. This would indicate that some aspects of nose shape may indeed have been driven by local adaptation to climate.

 
The investigation of nose shape evolution with respect to climate adaptation, while interesting anthropologically, is also relevant medically. As humans are becoming more of a global community, the study of local adaptation is becoming more important to understanding health risks involved in living in ‘foreign’ climates. Obvious examples of such health risks are of increased risk of sunburn, skin cancer, and folate deficiency in light-skinned individuals exposed to high UVB, and of low birth weight and chronic mountain sickness associated with hypoxia at high altitudes. Does the morphology of the external nose, or that of the inner nasal cavity affect risk of respiratory disease in different climates? It’s difficult to say at this point in time. Current findings provide support for the idea that differences in aspects of nose shape may have evolved across populations as a result of climate-related selection pressures, something that has been demonstrated previously using craniometric data. However, the signal of climate adaptation may not very strong, especially when compared to skin pigmentation. This could be due to weaker selection pressure or selection on standing variation, but also due the sparse sampling of populations used in investigations up to now. The findings will have to be replicated in larger sets of populations. Studies incorporating diverse populations who have been living long-term in a range of environments, such as the tropics, deserts, and circumpolar regions will nicely fill in these gaps in the future. Especially useful would be representation of populations from higher altitude regions, such as Andeans, Tibetans, and Ethiopians, who not only have to cope with the stress of a cold and dry climate, but also that of low atmospheric oxygen levels. It would also be informative to study non-human primates in this context, who occupy a variety of climes and exhibit extensive variation in nose morphology. Finally, future studies should also focus on genome-wide association studies (GWASs) to identify variants contributing to nose shape.
In fact, with increasing the interest in identifying loci associated with facial shape, some GWASs have already been performed that have recently identified a number of nose shape loci involving the five candidate genes PRDM16PAX3TP63C5orf50, and COL17A1. Genetic variation at these loci will be informative about the nature of selection, as well as for inferring the timing of selection events.
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Ph.D.; Professor in Pharmacology and Toxicology. Senior expert in theragenomic and personalized medicine and individualized drug safety. Senior expert in pharmaco- and toxicogenetics. Senior expert in human safety of drugs, chemicals, environmental pollutants, and dietary ingredients.

Posted in Genetic Background, New Research, Thasso Post, Theragenomic Medicine
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