Science Literature

It has long been recognised that Darwinists love to propose adaptationist stories about the origins of particular traits. Very few of them have the word "spandrel" in their working dictionaries. The Neanderthal nose has been considered as an adaptive structure: there must be a reason why Neanderthals had such big noses.

This gent uses XXL tissues. (Source here)

Some years ago, during a study of Neanderthal skulls, Schwartz and Tattersall identified "two triangular bony projections jutting into the front of the nasal cavity from either side". This was considered significant.

"Jeffrey Laitman, an anatomist at Mount Sinai Medical Center in New York who has been studying Neanderthal anatomy, thinks the bony structures probably helped Neanderthals breathe the cold air of Ice Age Europe. The jutting projections, Laitman suggests, could have provided more surface area on which to lay down mucosal coverings to warm and humidify cold, dry air before it reached the throat and lungs. Previous studies have suggested that the large sinus cavities of Neanderthals served a similar function." (Source here)

So, the argument went, the extra surface area was a more efficient heat transfer mechanism, allowing air to be warmed and humidified more effectively before reaching the lungs. This benefit was of adaptive significance to the Neanderthals, and natural selection ensured that the genetic instructions for making these large noses were passed on to subsequent generations. In a Commentary essay, Laitman et al. (1996) thought they were on to something really important:

"The acquisition and processing of oxygen and its by-products the primary mission of any air-breathing vertebrate. Chewing, walking, reproducing, thinking are all fine, but first one has to breathe. Anthropologists sometimes seem to forget this; evolution never does." [snip]
"[. . .] the overall Neanderthal anatomy suggests a group that relied more heavily upon the nasal rather than the oral route for respiration then do living humans. These specializations were very possibly due to respiratory-related adaptations to their environment. [. . .]"
"Although the exact function(s) of mammalian paranasal sinuses remains unclear, and have indeed become the focus of much recent study, it is likely that in Neanderthals they played at least some part in an air-exchange process, perhaps in warming and humidifying cold and dry air."

Notwithstanding all this, some remained unconvinced about the "respiratory-related adaptations". Callaway writes:

"The Neanderthal nose has been a matter of befuddlement for anthropologists, who point out that modern cold-adapted humans have narrow noses to moisten and warm air as it enters the lung, and reduce water and heat loss during exhalation. Big noses tend to be found in people whose ancestor's evolved in tropical climates, where a large nasal opening helps cool the body."

These scholars regarded the Neanderthal nose as an anomaly. Their preferred explanation was that a big nose goes with a big mouth and a wide jaw. In their view, Neanderthal features were all big, and this was sufficient to explain the facial features.

"To put this theory to the test, [Nathan Holton] and University of Iowa colleague Robert Franciscus, measured facial dimensions in dozens of Neanderthals and humans, ancient and modern. By correlating changes in the size of nose width, the distance between canine teeth, and other features, the researchers could determine whether or not big mouths went with big noses."

The results do not confirm the hypothesis. The researchers "found a slight link between nose and mouth, but not enough to explain Neanderthal noses. However, another measurement - the degree to which the face juts forward - seemed a better match for nose width." This suggests a developmental constraint rather than an adaptation.

Why, then, do Neanderthals have faces that jut further out than humans? "They had them because earlier hominids had them," Houlton says. He laments the tendency of some anthropologists to "atomise the body", and explain each of its part as an exquisite adaptation to an environment.

One additional research finding puts a different light on the adaptationist story noted above: "Fortunately for Neanderthals, their inner noses were narrower than the openings suggest, and therefore well adapted to bone-chilling winters." The moral of this incident seems to be: do not trust adaptationists who "atomise" the body and propose just-so stories for particular elements. Organisms are not collections of discrete elements but should be considered holistically. Evolutionary biologists have drunk too deeply at the well of reductionism.

The paradox of a wide nasal aperture in cold-adapted Neandertals: a causal assessment
Nathan E. Holton and Robert G. Franciscus
Journal of Human Evolution, Article in Press | doi:10.1016/j.jhevol.2008.07.001

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. [. . .] 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.

See also:

Callaway, E. Why did Neanderthals have such big noses?, New Scientist, 27 October 2008

Laitman, J.T., Reidenberg, J.S., Marquez, S. and Gannon, P.J., What the nose knows: new understandings of Neanderthal upper respiratory tract specializations, Proceedings of the National Academy of Sciences, 1996 93(20), 10543-10545.

Schwartz J.H. and Tattersall, I., Significance of some previously unrecognized apomorphies in the nasal region of Homo neanderthalensis, Proceedings of the National Academy of Sciences, 1996 93(20), 10852-10854.