In the late 1800s, British anthropologist and anatomist Arthur Thomson posited that people with ancestral origins in cold, arid climates were likely to have longer, thinner noses, while those who came from warm, humid regions were inclined to have noses that were shorter and thicker.
Over the years, scientists have tested Thomson's Nose Rule, as it came to be known, with skull measurements, but until recently no one had ever studied these dimensions in live people.
Pennsylvania State University researchers did just that in a study published Thursday in PLOS Genetics, confirming that Thomson was onto something. They concluded that the size and shape of noses evolved, at least in part, as a response to local climate conditions.
“We are primarily interested in understanding how human variation arises,” says Arslan Zaidi, a postdoctoral fellow in biology and the study's lead author. “The questions we ask are: why do we look different from one another? Why do males and females look different? Why are there differences among humans from different populations? We focused on the nose because there is a huge body of work suggesting that it may have evolved in response to climate.”
The research is important because studying human evolution and adaptation can have significant implications for human health. For example, people of Northern European ancestry — because of their light skin — carry an increased risk of sunburn and skin cancer when they are near the equator. Similarly, dark-skinned individuals carry an increased risk of vitamin-D deficiency at higher latitudes.
“These risks are a direct consequence of our evolutionary history,” Zaidi says. “Dark skin evolved to protect us from overexposure to ultraviolet radiation, and lighter skin evolved to allow us more absorption of UV so that we can synthesize more vitamin D. If nose shape evolution has indeed been driven by climate, does moving to a different climate increase our risk of respiratory disease? This is unclear at this point, but important to pursue.”
The researchers looked at a variety of nose measurements. Using three-dimensional facial imaging, they examined the width of the nostrils, the distance between nostrils, the height of the nose, nose ridge length, nose protrusion, external area of the nose, and the area of the nostrils. They focused on individuals of four different ancestries: South Asian, East Asian, West African and Northern European.
They asked two questions: Are some aspects of nose shape more varied across populations than expected with genetic drift? (Genetic drift is a random evolutionary process leading to differences among populations over a long period of time, simply by chance.) If so, can this variation be explained by climate?
“In other words, if two populations are isolated for a long time, we expect their noses to look different just by chance, because of genetic drift,” Zaidi says. “We needed to rule this out to show that the variation among human populations was more than that expected just by genetic drift. Out of the seven measurements describing nose shape, we found two measurements related to the width of the nose to be significantly more differentiated among populations than expected by genetic drift. This means that the difference in nose width among human populations is more than is expected by random chance.”
Researchers found a positive correlation between nostril width and temperature and humidity, suggesting that natural selection likely plays a significant role in human nose evolution. Natural selection is the process by which organisms that are well adapted to their environment tend to survive and pass their traits to succeeding generations, while ill-adapted organisms tend to die off.
But humans have always moved around, and these days it's not uncommon for someone from a long line of cold climates to live by the equator. They'll likely sport the narrow nostrils of their forbears.
“Evolution takes a long time,” Zaidi says. “If nose shape has evolved in the past to adapt to local climate, it likely took tens of thousands of years. So, my great-great-great grandkids are likely still going to have wider noses — I'm Pakistani — even if they continue to live in a colder climate, as long as they continue to marry other South Asians.”
Moreover, “human variation does not agree with notions of race,” he adds. “There are more similarities among humans from different populations than there are differences, both genetically and phenotypically. Traits such as skin pigmentation and nose width appear more different because they are examples of external traits that are exposed to the environment, and have evolved faster than most other human traits. They are an exception rather than the rule. This is an important caveat to make, because people often tend to focus on differences and ignore the similarities.”
The researchers also noted that other factors may also be involved, such as gender differences. Men tend to be larger than women, for example, so their noses tend to be larger as well. Other variations emerge because people may prefer mates with smaller or larger noses. Still, concepts of beauty may be related to how well-adapted a nose is to the local climate, according to the scientists.
As for the future of the schnoz, Zaidi says that evolution is “a wildly random” process, making it difficult to predict what will happen to the human nose in response to global warming.
“Human evolution, at this point, is very different from evolution in the past,” he says. “Our lifestyles aren't what they used to be, and we move around the world way too much. That makes it very complicated to predict the future evolutionary trajectory of the nose with the changing climate.”
Marlene Cimons writes for Nexus Media, a syndicated newswire covering climate, energy, policy, art and culture.