A Nose In The Air: The Influence of Climate & Nose Morphology

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.”

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.

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?

3 thoughts on “A Nose In The Air: The Influence of Climate & Nose Morphology

  1. Thanks for this. Very interesting. It does not explain however why human noses evolved in the first place (vs chimps, gorillas etc.). To say that our nose is “a structure meant to humidify air and warm it, aside from assist in smell” (see article) is not currect IMO: nearly all mammals humidy & warm their breathing air without an external nose.

    Why do humans evolve external noses that don’t seem to serve any useful purpose – our smelling sensors are inside the head. Our nose is vulnerable to damage and the majority of primates and other mammals manage with relatively flat faces.
    Traditional explanations are that the nose protects against dry air, hot air, cold air, dusty air, whatever air, but most savannah mammals have no external noses, and polar animals such as arctic foxes or hares tend to evolve shorter extremities including flatter noses (Allen’s Rule), not larger as the Neanderthal protruding nose.
    The answer isn’t so difficult if we simply consider humans like other mammals.
    An external nose is seen in, for instance, elephant seals, hooded seals, tapirs, elephants, swine, and among primates the mangrove-dwelling proboscis monkeys. Various functions – often mutually compatible – have been proposed, such as sexual display (male hooded and elephant seal, proboscis monkey), manipulation of food (elephants, tapirs, swine), snorkel (elephants, proboscis monkey) and nose-closing aid during diving (most of these animals). These mammals spend a lot of time at the edge between land and water. Possible functions of an external nose in incipient aquatics are obvious: nose closure, snorkel, keeping the water out, digging in wet soil for food, etc. Afterwards, these external noses can also become used for other functions, such as sexual display (visual as well as auditive) in hooded and elephant seals and proboscis monkeys.
    What does this have to do with human evolution?
    The earliest known Homo fossils outside Africa – such as Mojokerto on Java, and Dmanisi in Georgia – are about 1.8 million years old. The easiest way to spread to other continents, and to islands such as Java and Flores, is along the seacoasts and from there inland along rivers. During the Glacials of Pleistocene epoch (the “Ice Ages”, from about 1.8 to 0.01 million years ago) most seacoasts were about hundred metres below the present-day sea level, so we don’t know whether or when Homo populations lived there, but seacoasts and riversides are full of shellfish and other foods that are easily collected and digested by smart, handy and tool-using “apes”, and are rich in brain-specific nutrients such as poly-unsaturated fatty acids (for instance, docosahexaenoic acid or DHA). If Pleistocene Homo spread along the coasts, beachcombing, wading and diving for seafoods as Sea Gypsies, Ama divers and Polynesian islanders still do, this could explain why Homo erectus got larger brains (DHA) and larger noses (parttime diving). Apparently, at the coasts they used stone tools to crack open shellfish, crabs and coconuts and to butcher stranded whales (Dungo V site, Baia Farta, Angola), at the riversides they butchered bovids that were trampled and drowned when crossing rivers during the trek, and in wetlands they killed or injured and let bleed to death large herbivores that were hindered in their movements in the mud.
    This littoral intermezzo – wading, swimming, beachcombing, long-distance walking and running along the water – could help understand not only why we like to have our holidays at tropical beaches eating shrimps and coconuts, but also why we became fat and furless bipeds with long legs, large brains and big noses.
    (“Oi, big nose!” New Scientist 2782 p.69 Lastword 16 October 2010)

  2. External nose + tightly curled scalp hair + protruding everted lips = Living in very small leopard-proof shallow-concave dome huts, physical sensing the interior in the dark = functional ‘antennae’. The change from sleeping in exposed great ape aerial-arboreal bowl nests to inverted dome huts on the rainforest floor (=round-shields, lifted/tilted for entry & egress, multi-functional sun-shade, rain-shed, foraging basket, baby cradle, hunting hide) combined with anti-insect smoldering fire produced selection for artificial-constructed habitat unique to Homo species.

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