The Curiously Significant Evolutionary Role Of Your Sinuses

April Flowers for – Your Universe Online

The maxillary sinuses are bulbous pouches on either side of the human nose. They are known for their ability to trap mucus and as well as their role in causing sinus infections. Scientists have long thought that they were an evolutionary relic of our distant past, with little or no present value. However, some researchers believe the maxillary sinuses still play an integral role in the shape and function of the nose.

A new study led by researchers at the University of Iowa has examined faces of African and European origin and concluded that the maxillary sinuses act as a cushion, changing size to make room for the nose. According to the study, the sinuses maximize the primary function of the nose, which is to make air as breathable as possible. For the first time, researchers have explained the anatomical interconnectedness of the maxillary sinuses and the shape of the nasal cavity.

The results of this study were published in the journal The Anatomical Record.

The maxillary sinuses “allow the nose to change shape without affecting other areas of the face,” explains Nathan Holton, a biological anthropologist at the University of Iowa. “When something is under selective pressure like the nose, that´s a good thing.”

Like neighbors sharing a duplex, the nose and the maxillary sinuses share a common wall. And much like those proverbial neighbors, it is important whether the nose and maxillary sinuses are on good terms. To maximize function in relation to the climate where an individual lives, the nose has to be able to assume different shapes and change that shape without shifting around everything else in the face and cranium. In other words, the nose has evolved depending on what type of climate the human population lives in.

When humans live in colder climates, the nose evolved to be narrower and longer to better trap air in the nasal passage. In this manner, the air is warmed and moistened before it enters the lungs. However, put those same humans in a warm climate and the nose evolves to be broader and shorter, transporting the already warm and moist air to the lungs more quickly rather than letting it reside in the nasal passages. In broad terms, this explains the long, narrower, prominent bent of the typical northern European noses as well as the flatter, broader shape of the African nose.

To better understand this anatomical-evolutionary relationship, the team took computer tomography scans of 40 individuals evenly divided between European and African ancestry.  They wanted to understand whether a larger nose would mean smaller maxillary sinuses or vice versa. However, their findings defied expectations.

“What we found is that a bigger nasal volume was associated with a bigger sinus volume in both African and European samples,” Holton explains. “This is best explained as an overall size dynamic. Individuals with a bigger face also have a bigger nasal cavity and bigger maxillary sinuses.”

Concluding that nose shape must play a more pronounced role than previously thought, the research team then mapped the shape of the individuals’ nasal cavities by plotting points at different places in a grid. They found that in faces of similar size, maxillary sinuses in the European-derived subjects were on average 36 percent larger than those of African origin. The reason for this difference, they believe, is that the narrower European noses leave more room for larger maxillary sinus cavities.

“Essentially, by having these sinuses, that´s what allows the nose to change its shape, at least in terms of width and independently from other parts of the face,” explains Holton.

Considering that the nose needed to change according to the climate in which our ancestors lived, this evolutionary adaptability was extremely important in allowing early Homo sapiens to spread out to different geographical regions and climates around the planet — from the sweltering dry heat of Sub-Saharan Africa to the bone-chilling subzero temperatures of northeastern Siberia.

According to the researchers, far from being insignificant and obnoxious vestiges of our past, our maxillary sinuses act as critical “zones of accommodation.”

“Our results suggest that while the sinuses are unlikely to play a direct role in nasorespiratory function, they are important with regard to accommodation of climatically relevant changes in internal nasal shape,” the authors wrote.

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