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British anthropologist Arthur Thomson, in the late 1800’s published his observations on nose size and shape. He noted that humans from humid, warm climates have wider, shorter noses than humans from colder, dryer climates who have more narrow, longer noses. He carried on his observation postulating that the shape of the nose was influenced by the climate. The shape of a nose, a structure meant to humidify air and warm it, aside from assist in smell was more determined by climate than any other factor. Thomson’s Nose Rule, as it is known now, is taught in many biological anthropology courses. No one however has studied the how and why… Until recently.

PLOS Genetics study published yesterday affirms that Thomson was actually sniffing up that exact pole. The authors primarily looked to understand how human variation arose. Arslan Zaidi, a postdoctoral fellow in Penn State’s department of biology and the lead author asks,

“…why do we look different from one another? Why do males and females look different? Why are there differences among humans from different populations? We focused on the nose because there is a huge body of work suggesting that it may have evolved in response to climate.”

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PLOS Genetics – This diagram represents the evolution of the human nose. Blue boxes, corresponding to colder climates, represent narrower nostrils. Red boxes, corresponding to warmer climates, represent wider nostrils. Colors in between represent intermediate nose shapes.

The team focused on South Asian, East Asian, West African and Northern European ancestries. They used 3D facial imaging and examined 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.

Then they asked two questions,

  1. Are there variations in nose shape within the expectations of genetic drift or more varied?
  2. If more varied, can climate be an influence?

They were able to identify a positive correlation between nostril width and temperature and humidity. This implies there is a selective force in the evolution of the human nose. In fact the researchers state it is the most influential factor to the size and shape of noses we see; validating Thompson’s theory.

What about culture? With an equal distribution of males to females in the four regions why do males tend to have larger noses than females (Fig 2, below). Does this variation occur because humans prefer mates with smaller or larger noses… A element of sexual selection.

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Fig 2. Boxplots of phenotypes by population and sex overlaid with the individual data points. Height is measured in centimeters and melanin index is measured in percentage reflectance (Methods). Linear distances are measured in millimeters (mm) and area are measured in mm2. Points are individual observations and the color of the boxplots and points represents sex with blue indicating males and red indicating females.

I certainly think cultural concepts of beauty may be related to how well-adapted a nose is to the local climate. But paper implies the selective pressure of climate outweighs that of culture. So why then are female noses smaller than males of the same climate, when adjusted for differences of body habitus?

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