|Image: © iStock Photo kowalska-art|
Scientists believe they have uncovered evidence that the different human nose types are at least partly or even mostly adaptations to different climates as humans spread out from our ancestral homeland in Africa.
An important function of the nasal cavity and the nasopharynx is to humidify the sir before it reaches the lower respirator tract and the lungs.
Using 3D facial imaging, the team measured the width of the nostrils, the distance between nostrils, the height of the nose, nose ridge length, nose protrusion, external area of the nose and the area of the nostrils. They found the two measures: the width of the nostrils and of the base of the nose differed between different human populations by more than would be expected from genetic drift alone. They found a positive correlation between the width of the nose and the warmth and humidity of the climate in which the populations lived.
We are interested in recent human evolution and what explains the evident variation in things like skin color, hair color and the face itself. We focused on nose traits that differ across populations and looked at geographical variation with respect to temperature and humidity.This idea is not a new one. In the 1880s, anatomist Arthur Thompson devised 'Thompson's Rule' when he noticed that long narrow noses were more common in cold, dry areas and short, wide noses in hot, humid areas. There have since been various attempts to prove this statistically by measuring skeletons, but this is the first study to use live subjects.
Mark D. Shriver. Professor of anthropology, Penn State.
The study also noted a degree of sexual dimorphism so climate-related adaptive evolution is probably not the only factor involved in the evolution of the human nose. Genetic drift and sex selection may also have played a part as might founder effects as humans spread out into previously uninhabited lands as small extended family bands. Each more or less isolated group would have had only the random sample of the total human gene-pool of that small groups, which may well not have been representative of the whole gene pool.
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, we use Qst–Fst comparisons 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 is due to climate adaptation, we compared the spatial distribution of these variables with the global distribution of temperature, absolute humidity, and relative humidity. We find that width of the nares is correlated with temperature and absolute humidity, but not with relative humidity. We conclude that some aspects of nose shape may indeed have been driven by local adaptation to climate. However, we think that this is a simplified explanation of a very complex evolutionary history, which possibly also involved other non-neutral forces such as sexual selection.
The study of human adaptation is essential to our understanding of disease etiology. Evolutionary investigations into why certain disease phenotype such as sickle-cell anemia and lactose intolerance occur at different rates in different populations have led to a better understanding of the genetic and environmental risk factors involved. Similarly, research into the geographical distribution of skin pigmentation continues to yield important clues regarding risk of vitamin D deficiency and skin cancer. Here, we investigate whether variation in the shape of the external nose across populations has been driven by regional differences in climate. We find that variation in both nares width and alar base width appear to have experienced accelerated divergence across human populations. We also find that the geospatial distribution of nares width is correlated with temperature, and absolute humidity, but not with relative humidity. Our results support the claim that local adaptation to climate may have had a role in the evolution of nose shape differences across human populations.
Zaidi AA, Mattern BC, Claes P, McEcoy B, Hughes C, Shriver MD (2017)
Investigating the case of human nose shape and climate adaptation.
PLoS Genet 13(3): e1006616. doi:10.1371/journal.pgen.1006616
Copyright: © 2017 Zaidi et al. Open access.
Reprinted under the terms of a Creative Commons Attribution 4.0 International license (CC BY 4.0).
So we see here yet another example of how the Theory of Evolution provides the framework for understanding human diversity. It's hard to see where creationists get the idea that somehow the TofE is a theory in some sort of crisis, increasingly incapable of explaining the observable evidence. Apart from their own desperate wishful thinking, there would appear to be no reason at all to think this could be even remotely true.
'via Blog this'