A new study suggests that the current shape of human nose is a result of the local climate of our ancestors, as well as how they evolved with the changes in climate. Photo Courtesy:-Nariz

Humans inherit their nose shape from their parents or grandparents, but ultimately, the size and shape of someone’s nose and that of their parents was formed by a long process of adaptation to local climate, according to new research. Birthplace, local climate conditions and temperature can all have an effect on the size and shape of the human nose. Researchers have found evidence for natural selection’s role in the evolution of nose shape in people. The new findings are published Thursday (March 16th, 2017) in the journal PLOS Genetics.

“We are interested in recent human evolution and what explains the evident variation in things like skin color, hair color and the face itself,” said Mark D. Shriver, professor of anthropology, Penn State. “We focused on nose traits that differ across populations and looked at geographical variation with respect to temperature and humidity.”

In the late 1800s, Arthur Thomson – a British anatomist and anthropologist pointed out that people with ancestral origins in cold, dry environments were likely to have longer, thinner and narrower noses, while those people came from hotter, more humid areas were inclined to have noses that were shorter, wider, and thicker. This rule is now referred to as Thomson’s nose rule.

Researchers at Pennsylvania State University said their new study supported the popular theory of Thompson’s Nose Rule. The nose is one of our most distinctive characteristics and its primary functions are breathing and smelling. The nose also has the important role of conditioning the air that we breathe, it has mucous and blood capillaries inside to ensure that the inhaled air is warm and humidify before it reaches more sensitive parts of the respiratory tract, which helps to prevent infections.

Blue boxes represent alleles for narrower nares while red boxes represent alleles for wider nares. Colours in between represent intermediate phenotypes. The colour scale represents climatic variation in temperature and humidity, to show that narrower nares are favoured in cool-dry climates while wider nares are favoured in hot-humid climates. Photograph:- Arslan A. Zaidi and colleagues

“An important function of the nose and nasal cavity is to condition inspired air before it reaches the lower respiratory tract,” the researchers noted in PLOS Genetics.

Previous studies suggest that people whose ancestors lived in hot, humid places tend to have wider nostrils than people whose ancestors came from cold and dry environments. This suggests it is an advantage for people in colder climates to have narrower nostrils. And having narrower nasal airways might help increase contact between inhaled air and tissues inside the nose carrying moisture and heat, said Penn State University geneticist Arslan Zaidi, lead author of the study published in the journal PLOS Genetics. Additionally, wider nostrils are correlated with ancestors who evolved in warmer temperatures and with greater absolute humidity, suggesting that climate was one factor driving nasal evolution.

Although the rule is well-established, but it was not clear whether these differences arose as a response to selection pressures, or whether it was simply due to genetic drift. Differences in the human nose- big, little, broad, narrow, long or short, turned up, pug, hooked, bulbous or prominent- may have accumulated among populations through time as a result of a random process called genetic drift.

Thomson’s Nose Rule has previously been examined by measuring skulls but, for the first time, the theory has been tested using live humans and 3-D facial imaging. Researchers set out to uncover whether nose size evolved as an adaptation to climate. They concluded that the size and shape of the nose in different human populations is not simply the result of chance, but evolved, at least in part, as a response to local climate conditions.

A) The locations of landmarks, which were used to calculate linear distances, are shown as red points. B) Five Linear distances (red lines) and two surface areas (red mesh) were used to describe nose shape. Linear distances were calculated from the 3D coordinates of landmarks (red points). Surface areas were computed as the sum of the polygons highlighted in red. Photo Courtesy:- Arslan A. Zaidi, Brooke C. Mattern, Peter Claes, Brian McEcoy, Cris Hughes, Mark D. Shriver

The team, led by Arslan Zaidi and Mark Shriver of Pennsylvania State University in the US, examined three-dimensional images of hundreds of people of West African, East Asian, South Asian and Northern European ancestry, measuring their width and height. A major part of the study contains 3D scanning of the faces of more 10,000 people to examine features, which may differ continuously within minutes. Shiver and his other team members chose 2,637 people from a database of over 10,000 individuals.

Dr Mark Shriver and his colleague Arslan Zaidi considered a variety of nose measurements, looking at 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.

The researchers studied the noses of people with west African, south Asian, east Asian, and northern European ancestry. Photo Courtesy:- Arslan A. Zaidi and colleagues.

They conducted a statistical analysis to determine if the differences might be explained by genetic drift — normal variation in natural selection across populations that develop over time — alone. The researchers found that the width of the nostrils and the base of the nose measurements differed across populations, indicating a role for natural selection in the evolution of nose shape in humans. In fact, temperature and humidity appear to play very important roles.

The researchers noted that “the positive direction of the effects indicate that wider noses are more common in warm-humid climates, while narrower noses are more common in cold-dry climates.”

“It all goes back to Thompson’s Rule (Arthur Thompson),” said Shriver. “In the late 1800s he said that long and thin noses occurred in dry, cold areas, while short and wide noses occurred in hot, humid areas. Many people have tested the question with measurements of the skull, but no one had done measurements on live people.”

Researchers also noted that natural selection isn’t the only possible explanation for nose-shape variation in humans. Sexual dimorphism may also have played a role, with people choosing mates because they find a smaller or larger nose more attractive. They also found differences between men and women in nose features across the board, for example, men’s noses were larger, on average, than women’s noses.

The current findings could also have medical implications for medicine, particularly as people travel more around the world, the study said. For example, the researchers asked if someone (he or she) lived in a hot and humid climate with a narrow nose, he or she could have an increased risk for respiratory problems.

Original Source:- Penn State