How Your Nose Got Its Shape

Climate variation has sculpted our schnozzes since the earliest humans evolved, but environmental pressures can’t explain everything.

By Karen Zusi | August 1, 2016

THE NOSE KNOWS: Nose shapes in human ancestors and different populations of modern humans are molded by genes and the environment.COURTESY OF KAUSTUBH ADHIKARI

Narrow, flat, hooked, button, straight, or none of the above, the human nose comes in myriad shapes and sizes. But no matter how noses look, they all share at least one common function: to warm and humidify air on its way to the lungs. Like a wind tunnel, the nasal passages cause turbulence in inspired air, allowing it to touch the inner walls of the nose and draw moisture and heat from our mucosa and blood vessels.

The shape of the human nose has been sculpted in part by climate. “A lot of it depends on the environment that your ancestors grew up in,” says Lauren Butaric, a biological anthropologist at Des Moines University. “What you see in the cartilaginous structure, which matches up with the internal structure, is that individuals from cold, dry environments tend to have tall and narrow nasal cavities.” In the wide noses often seen in individuals with tropical ancestry, Butaric adds, the air flow is much smoother, traveling straight back with less warming and humidification.

Butaric and her colleagues recently determined that in Alaskan Inuit and Siberian Buryat populations, a longer, narrower nasal cavity is associated with large maxillary sinuses, and in sub-Saharan African populations, the wider nasal cavity is accompanied by smaller maxillary sinuses (Am J Phys Anthropol, 160:483-97, 2016). The sinuses function as a sort of “buffer” to accommodate changes in the nasal cavity and other structures of the face, Butaric’s team concluded, both during an individual’s development and over evolutionary time.

The relationship between sinus and nasal cavity shape has historically created a paradox for anthropologists when it comes to archaic human species. “The sexy topic is Neanderthals,” says Butaric. Many scientists have assumed these ancient populations were more adapted to cold weather than Homo sapiens are, even those H. sapiens at high latitudes, because the Neanderthals were associated with colder and drier conditions during Earth’s glacial periods. Accordingly, a typical Neanderthal’s sinuses were thought to be larger than a modern-day human’s would be if the human was otherwise a similar size. However, instead of a long, narrow external nose structure, the Neanderthal face most likely had a relatively wide nose, judging from bone morphology.

“[Neanderthals] look like they should be adapted to being in warm and wet environments, not cold, dry ones,” says Todd Rae, an anthropologist at the University of Roehampton in the U.K. Delving into the internal facial structures, Rae and colleagues used CT scans to compare Neanderthal skulls to H. sapiens fossils from Lithuanian archaeological sites, testing the assumption that the Neanderthal sinuses were relatively larger. Their data showed that the Neanderthal sinuses were not, in fact, any larger than a human’s would be if the entire skull was scaled to the same size.

“That suggested to us that [Neanderthals were] not especially cold-adapted,” says Rae. Expanding this reasoning to the external nose, Rae hypothesized that the wide-nosed Neanderthal face wasn’t an adaptation to the cold at all, but was driven by some other underlying factor (J Hum Evol, 60:234-39, 2011).

Butaric suggests that the Neanderthals, with larger bodies and more muscle mass, might have needed larger noses to inhale appropriate amounts of oxygen, regardless of where they lived. In modern humans, males generally have larger noses and nasal passages than females do, which may be due to a higher oxygen demand (Am J Phys Anthropol, 160:52-61, 2016). Another possible explanation, Rae proposes, is that the Neanderthals may have simply avoided the extremely cold areas during times that would have provided enough selection pressure to mold their noses into a narrow shape.

In human evolution, weather isn’t everything, either. We’ve mostly shaped the world around us to avoid the selection pressure of extremely cold environments. Work on cranial morphology suggests that much of the skull variation in today’s human populations is explainable more by distance from Africa than by adaptation to the local environment (Am J Phys Anthropol, 141:76-82, 2010). “We think it might just be drift—that simply the further you get, the more a population will start to develop differences from copying errors in DNA,” says Rae. “You’re going to get the narrow nose in places where it’s really cold, but [also] where it’s relatively temperate; the differences are literally random.”

Although these nasal differences in temperate zones may not be driven by environmental variables, geographically related traits are still evident. “There is wide variation across continents, and that sort of tells you that there are underlying genetic reasons,” says Kaustubh Adhikari, a population geneticist at University College London. Adhikari and his colleagues recently published a paper exploring the genetic variations associated with differences in external nose shape (Nat Commun, 7:11616, 2016).

Earlier studies had uncovered a few genes that play a role in sculpting our noses, but much of the work was done in homogeneous European or North American populations with small morphological differences. Adhikari’s team, however, collected genetic samples and facial photographs from a cohort of more than 6,000 Latin Americans across five countries. “Latin America is a genetic melting pot,” explains Adhikari. “You have the Native Americans, who are close to East Asians; you have Europeans, and you have Africans—and you have all of these just on one continent. And the admixture is very recent.”

Adhikari and his colleagues detected five genes that controlled some aspect of nose structure. All five genes affect bone or cartilage differentiation and cranio-facial development, and three have previously been identified as differing between modern humans and extinct species such as Neanderthals and Denisovans—both of which had slightly different nose shapes than H. sapiens. “It’s not the complete story,” says Adhikari, “but it’s a little piece of it.”

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Avatar of: marc verhaegen

marc verhaegen

Posts: 17

August 4, 2016

"Oi, big nose!" New Scientist NS 2782 p 69 Lastword 16 October 2010

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 elephant seals, hooded seals, tapirs, elephants, swine and, among primates, in the mangrove-dwelling proboscis monkeys. Various, often mutually compatible functions, have been proposed, such as sexual display (in male hooded and elephant seals or proboscis monkeys), manipulation of food (in elephants, tapirs and swine), a snorkel (elephants, proboscis monkeys) and as a nose-closing aid during diving (in most of these animals). These mammals spend a lot of time at the margins of land and water. Possible functions of an external nose in creatures evolving into aquatic ones are obvious and match those listed above in many cases. They can initially act as a nose closure, a snorkel, to keep water out, to dig in wet soil for food, and so on. Afterwards, these external noses can also become co-opted for other functions, such as sexual display (visual as well as auditory) in hooded and elephant seals and proboscis monkeys.

But what does this have to do with human evolution?

The earliest known Homo fossils outside Africa – such as those at Mojokerto in Java and Dmanisi in Georgia – are about 1.8 million years old. The easiest way for them to have spread to other continents, and to islands such as Java, is along the coasts, and from there inland along rivers. During the glacial periods of the Pleistocene – the ice age cycles that ran from about 1.8 million to 12,000 years ago – most coasts were about 100 metres below the present-day sea level, so we don’t know whether or when Homo populations lived there. But coasts 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 potential brain-boosting nutrients such as docosahexaenoic acid (DHA).

If Pleistocene Homo spread along the coasts, beachcombing, wading and diving for seafoods as Polynesian islanders still do, this could explain why Homo erectus evolved larger brains (aided by DHA) and larger noses (because of their part-time diving). This littoral intermezzo could help to explain 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.

Avatar of: James V. Kohl

James V. Kohl

Posts: 531

Replied to a comment from marc verhaegen made on August 4, 2016

August 4, 2016

Thanks for mentioning docosahexanenoic acid. Nose width and breadth can also be placed into the context of "A quantum theory for the irreplaceable role of docosahexaenoic acid in neural cell signalling throughout evolution"

Unfortunately for neo-Darwinian theorists, quantum theory eliminates every aspect of their theories by making all cell type differentiation nutrient energy-dependent and all pathology due to virus-driven energy theft.

See: Epigenetics and Genetics of Viral Latency

Excerpt: "...viral latency is responsible for life-long pathogenesis and mortality risk..."

Avatar of: James V. Kohl

James V. Kohl

Posts: 531

August 4, 2016

A genome-wide association scan implicates DCHS2, RUNX2, GLI3, PAX1 and EDAR in human facial variation

This open access article links a single energy-dependent change in one base pair from EDAR to the nutrient energy-dependent receptor-mediated Val370Ala amino acid substitution, which is also known as 1540T/C and 370A.

The Val370Ala is a SNP in the ectodysplasin A receptor EDAR gene on chromosome 2, which appears to link the pheromone-controlled physiology of reproduction to chromosomal rearrangements in species from microbes to humans via species-specific RNA-mediated amino acid substitutions that stabilize biophysically-constrained protein folding chemistry.

RNA methylation links the substitutions from the innate immune system to supercoiled DNA via everything known about the energy-dependent links from angstroms to ecosystems in the context of links from metabolic networks to genetic networks. See for instance: Structural diversity of supercoiled DNA.

See for comparison: Mutation-Driven Evolution

Avatar of: marc verhaegen

marc verhaegen

Posts: 17

August 4, 2016

The comparative evidence suggests that neandertals had bigger noses than we have, because they were wetland dwellers. There's a strong correlation between paranasal sinus size & projecting nostrils: elephants, swine, tapirs & also neandertals, which suggests they spent a lot of time in (fresh)waters. Indeed, neandertal tools sometimes bear traces of cattails (which grow in wetlands), and their dental plaque has traces of waterliliy roots (which can be harvested by diving). All neandertal fossils lay in river valleys & oxbow lakes near beavers & reeds, or else at seacoasts from Gibraltar to Greece. Seafood such as shellfish is extremely rich in brain-specific nutrients (DHA, taurine, iodine), which helps explain their big brains. Neandertals had limited pachy-osteo-sclerosis or thick & dense bones (more than sapiens, less than erectus), which is exclusively seen in littoral anmals. Conclusion: most likely, neandertals seasonally followed the river to the coast.

Avatar of: James V. Kohl

James V. Kohl

Posts: 531

Replied to a comment from marc verhaegen made on August 4, 2016

August 4, 2016

The comparitive experimental evidence of biologically-based cause and effect does not support any evolutionary theories. It supports use of what is known about biophysically constrained energy-dependent RNA-mediated protein folding chemistry in the context of a model that links energy-dependent chemotaxis and phototaxis to the physiology of reproduction in species from microbes to humans.

Indeed, in the case of higher animals we know the kind of orderliness they feed upon well enough, viz. the extremely well-ordered state of matter in more or less complicated organic compounds, which serve them as foodstuffs. After utilizing it they return it in a very much degraded form -not entirely degraded, however, for plants can still make use of it. (These, of course, have their most power supply of ‘negative entropy’ the sunlight) - Schrodinger (1944)

 

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