An energy-efficient nose

Richard Casement Internship sample, The Economist

Visitors to a human evolution exhibit at the museum might not immediately recognize a reconstructed Neandertal as a close relative. Much of this lack of recognition would stem from the species' distinctive facial anatomy, which features a very large, very projecting nose.

This peculiar nose is the subject of much study, mainly because the nasal design of indigenous peoples reflects the climate they live in, and by extension, the climate that they may have evolved in. For example, Eskimos have narrow noses (which increase airflow turbulence) to warm and humidify the cold, dry air of their frozen environment. This process of warming and humidifying inhaled air within the nose prevents damage to the lungs. By contrast, the people of equatorial Africa have broader noses (which minimize turbulence) to avoid heating inhaled air.

Neandertals lived in cold climates, and yet their noses were wide and broad, with large nasal cartilages, features typical of noses adapted to warmer, wetter climates. This puzzle intrigued Steven Churchill, of Duke University, who set out to test the widely believed theory that the Neandertal's odd nasal structure enhanced turbulence. He created an experiment to examine the great variation in modern human noses, which, once analyzed, would shed light on the adaptive significance of the Neandertal nose.

Though the nose seems straightforward enough, a peek within reveals it to be a far more complicated structure. There are variations in the bony shelves within the nose (known as conchae), the height of the nasal floor, the angle of bones of the nose, and so on. Dr Churchill reasoned that by studying this variation in modern cadaver noses, he could come close to determining which features led to turbulent versus smooth airflow.

Analyzing water and dye (used to make flow patterns visible) as it flowed through anatomically accurate nasal models, Dr Churchill found that nasal flow patterns are highly variable from person to person. Previous studies using a single physical or computer model had concluded that airflow was either definitively smooth or turbulent. He also discovered that the features of modern noses that most closely mimicked Neandertals' features created smooth streamlines within the rough airflow.

Dr Churchill's results indicated that the modern human nose, which is relatively simple in design compared with the Neandertal's, has no problem producing turbulence at any flow rate. The significance of the Neandertal's complex turbulence-minimizing features remained a mystery.

Turning to the Neandertal's environment, climate, niche, and fossil remains for clues, Dr Churchill found an answer that satisfied him.

Neandertals had large chests and very thick, robust bones, which indicate a high physical activity level for the species. The Neandertals, a highly active species in a cold, dry habitat, were constrained to nose breathing (mouth breathing being too inefficient), and struggled to find food, which was quite limited.

The connection between nose breathing, exertion and diet seems an odd one, but since the simple act of breathing takes energy—hundreds of calories a day for a modern human—the Neandertal, in its evolution, would have undergone an intense selective pressure to conserve energy wherever possible.

This led Dr Churchill to the idea that the Neandertal nose needed to be more energy efficient, since the Neandertals lived on the very edges of their caloric budgets. An evolutionary compromise was struck: Slightly drier, colder air in exchange for a lower cost of breathing.

Since the Neandertals persisted for about 200,000 years, something in their unique anatomy allowed them to be successful. While the nose itself was probably not the sole trait that led to their endurance, Dr Churchill believes that it was certainly part of a suite of adaptive characteristics that gave the Neandertals their longevity. Indicating, perhaps, that it was not such a superfluous snout, after all.

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