October 15, 2008

Why did Neanderthals have broad noses?

Neanderthals had a generally wide nose opening. In recent humans, such a feature is found mainly in the inhabitants of equatorial regions, while populations away from the tropics have a narrower nose. Neanderthals occupied a relatively cold and dry region of the world, so they ought to have relatively narrow noses, but they didn't. What accounts for this discrepancy?

To explain this phenomenon, it was proposed that Neanderthals were constrained to have wide noses by their wide mouths, especially the distance between their front canine teeth (ICB), which effectively "pulled to the sides" their midfacial region. Neanderthals may have needed to have such broad mouths to aid chewing.

Interestingly, a broad dental arch is associated with facial prognathism, i.e., the degree to which the face juts forward. So, perhaps Neanderthals possessed this trait because they retained the ancestral trait of prognathism. Prognathism can be measured by the basion-prosthion length (BPL), roughly the distance between the hole at the bottom of the skull and the point between the front two teeth.

It turns out that BPL rather than ICB explains more variance in the breadth of the nasal aperture, and hence this tends not to support the theory that Neanderthals had broad noses because they had wide palates.

So, how did Neanderthals manage to have broad noses against ecological expectation? They were "forced" to have such noses because of their substantial prognathism. But, their nasal heights were also great, and hence their nasal index (breadth/height) was fairly low. Thus, they may have dealt with their cold and dry environment by having a broad and long nose, rather than a short and narrow one.

Journal of Human Evolution doi: 10.1016/j.jhevol.2008.07.001

The paradox of a wide nasal aperture in cold-adapted Neandertals: a causal assessment

Nathan E. Holto, Robert G. Franciscus

Abstract

Neandertals have been characterized as possessing features indicative of cold-climate adaptation largely based on ecogeographical morphological patterning found in recent humans. Interestingly, one character that deviates from this pattern is a relatively wide nasal aperture. The ecogeographical patterning of the nasal aperture in recent humans would predict instead that Neandertals should exhibit reduced nasal breadth dimensions. To explain this apparent anomaly it has been argued that a reduction in Neandertal nasal breadth was not possible due to dentognathic constraints on their midfaces via large anterior palatal breadth dimensions, especially large intercanine distances. A complicating factor in understanding the relationship between anterior palate breadth and nasal breadth is that both measurements are also correlated with facial prognathism. It is, therefore, unknown to what degree the relationship between anterior palate breadth and nasal breadth in Neandertals is a function of the pleisiomorphic retention of a prognathic facial skeleton. We used path analysis to test for a causal relationship between intercanine breadth and nasal breadth taking into account the potential effect of facial projection and facial prognathism (i.e., basion-nasion length and basion-prosthion length) using a large sample of geographically diverse recent and fossil Homo. Additionally, we examined the ontogenetic relationship between nasal breadth and intercanine breadth using a longitudinal human growth series to determine whether these variables exhibit similar growth trajectories. The results of these analyses indicate a weaker association between intercanine breadth and nasal breadth than expected, and that more variation in nasal breadth can be explained through basion-prosthion length rather than anterior palatal breadth dimensions. Moreover, the ontogenetic development of anterior palate breadth does not correspond to the growth trajectory of the breadth of the nose. These results explain the apparent paradox of wide piriform apertures in generally cooler climate-adapted Neandertals without resorting to dentognathic constraints, and provide additional insight into both the adaptive and nonadaptive (i.e., neutral) basis for Neandertal facial evolution.

Link

13 comments:

Crimson Guard said...
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Crimson Guard said...
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Crimson Guard said...

Its an interesting article, but whats the explanation on modern Europoid Phenotypes or Mongoloids which poses such similar traits?

Neanderthals mostly lived in the warmer temperate and more inhabitable areas of Paleolithic Europe, which was mainly Southern Europe and the Near East rather than the brutal inhospitable and barren colder Northern European areas as often portrayed.

Mongoloids posses often facial prognathism and generic broad noses. Many of them dont come from cold areas either.

Also aside from Semi-Mongoloid influenced Europoid types like(East Baltics, Lapps and Ladogans) with broad noses and often faces, like say Alpines/Borreby's and Dalo-Nordics/Paleo-Sardinians or Coon's Nordo-Mediterranean Alpine hyrids(ie Brunns)--Whats the story behind their associated traits often interpreted as being Neanderhtaloid derived or even cold weather derived? I dont think it pans out to well in either case. The so-called Paleo-Sardinia type shouldn't exist in the south and the Nordic shouldn't exist in the North then.

If early modern humans(namely Caucasoid came from Africa, whether it be North Africa or East Africa, the climate would not of produced broad noses or such robust facial traits. That area was quite green and temperate, neither the snow covered Alpine valley nor barren desert wastelands of the Sahara.

Maju said...

AFAIK, most archaic Homo sapiens also had broad (Negroid-like) noses (and prognathism too, sure). Think in Skuhl specimens, for instance. It may be just a general dominant trait from our common ancestors that they did not really need to alter.

The evolutionary explanation of nose shape is somewhat lacking anyhow. It may be more an identity/aesthetic trait actually, with a mere founder effect behind. Maybe Caucasoids favored somewhat prominent narrow noses in sexual selection just because they found them less Neanderthal-like, who knows?

Crimson Guard said...

Yeah well they will have also explain the Neanderthal's ancestor, Homo-Heidelbergensis' nose too...which had to have been broad as well but thrived in Southern Europe as well.

sanjeet said...
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ren said...

http://upload.wikimedia.org/wikipedia/commons/c/c2/Prince_Sultan.jpg

Neanderthals had "Caucasoid" noses, broad and prominent.

Maju, please try not to keep confusing narrowness with prominence, broadness with a "flat nose".

The average nasal width of certain Asian groups is narrower than that of certain European groups. Take 10 random northern Chinese and chances are reasonable that they would have narrower noses than 10 Italian Americans.

Dienekes said...

The average nasal width of certain Asian groups is narrower than that of certain European groups. Take 10 random northern Chinese and chances are reasonable that they would have narrower noses than 10 Italian Americans.

The nasal width of Italians is 32.1mm, the same as White Americans . The Japanese have nasal width of 38.2mm. What is your evidence that North Chinese have narrower noses than Italians?

ren said...

That's not what I said, Dienekes...
Anyway, I'd say four out of the five Korean guys in this picture have lower nasal width values than the Greek composite you have as your avatar.

Here are also some measurements:
http://img136.imageshack.us/img136/1439/27tableiib01uy4.jpg

ren said...

Forgot to link the pic:
http://www.stay-awake.org/wp-content/uploads/2007/08/n694391059_120777_2892.jpg

Dienekes said...

Nasal width of Korean American women is 35.5mm, of Greek women it is 32.4mm, and of Italian women it is 29.5mm (J Craniofac Surg. 2005 Jul ;16 (4):615-46)

sanjeet said...
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Ron said...

I think I know why their nasal cavity was so large - Neandertal needed A LOT of oxygen.

A. They were huge and muscular.
B. It was cold.

I imagine them breathing like a steam locomotive to fuel that inner fire! Especially if they were naked, or their primitive clothing was inadequate for the climate.

Why is this never mentioned?