Ask anyone what the nose does, and the reply will most likely be related to smell. We appreciate our noses because they help us experience flowers and fresh-baked cookies.

In fact, our honkers have another, more important function: They warm and humidify the air we breathe, helping prevent illness and damage in our airways and lungs. Because of this, scientists have long suspected that nose shape evolved partly in response to local climate conditions. In cold, dry climates, natural selection may have favored noses that were better at heating and moisturizing air.

A team led by scientists at Pennsylvania State University has found more evidence of the relationship between the noses we have now and the climates where our ancestors lived.

In a study published in PLOS Genetics on Thursday, the researchers found that nostril width differed significantly between populations from different regions around the world. Moreover, the higher the temperature and absolute humidity of the region, the wider the nostril, the researchers found, suggesting that climate very well may have played a part in shaping our sniffers

Physical traits that are in direct contact with the environment often undergo natural selection and evolve faster, said Arslan Zaidi, a postdoctoral scholar in genetics at Penn State and an author of the paper. “This is one of the reasons why we looked at nose shape.”

All in all, Dr. Zaidi and his colleagues measured seven nose traits, including the nose’s height, protrusion and nostril width, along with skin pigmentation and overall height in men and women whose parents were born in regions that corresponded with their genetic ancestry. They looked at four regions — West Africa, East Asia, Northern Europe and South Asia — with at least 40 participants in each group.

“We selected these to maximize the distance across populations,” Dr. Zaidi said, adding that his team wants to sample more groups in future research.

Between the groups in this study, only nostril width and skin pigmentation showed greater differences than would be expected because of chance accumulations of genetic mutations.

Over all, people whose parents and ancestors came from warm, humid climates tended to have wider nostrils, whereas those from cold, dry climates tended to have narrower ones. Correlations between nostril width and climate were strongest for Northern Europeans, the researchers found, suggesting that cold, dry climates in particular may have favored people with narrower nostrils.

These findings align with those of previous studies of the skull, which have shown that narrower internal nasal inlets tend to be more efficient at warming and humidifying air, said Katerina Harvati, director of the paleoanthropology department at the University of Tübingen in Germany, who was not involved in this study.

Dr. Zaidi and his colleagues also demonstrated that nose shape is a heritable trait. They did this by showing a relationship between shared genes and similarities in nose shape in large groups of unrelated people.

This is important because natural selection can act only on characteristics that can be passed from one generation to the next, said Todd Yokley, a biological anthropologist at the Metropolitan State University of Denver, who did not participate in the study.

The fact that nose shape is subject to natural selection and showed evidence of varying with climate paints a convincing picture that climate adaptation played some role in the evolution of nostril width, Dr. Zaidi said.

He added, however, that nostril width does not seem to correlate with climate as closely as skin pigmentation does. That may indicate that other factors are involved in what kinds of noses are passed down, he said, such as “cultural differences in what is considered an attractive nose or not.”

It’s also important to note that less than 15 percent of genetic variation in humans can be attributed to differences between people from different continents, Dr. Zaidi said.

In actuality, the genes that differ because of geographic origin, such as those affecting skin color, hair texture and nose shape, are the rare exception, rather than the rule.

“People are more similar than they are different. What this research does is offer people a view of why we’re different,” he said. “There’s an evolutionary history to it that, I think, kind of demystifies the concept of race.”

Studying how certain traits evolved as environmental adaptations that may no longer be relevant could also help us understand disease risk today, Dr. Zaidi said.

“We know there are variable risks of respiratory diseases across different populations in the U.S.,” he said. “Can we find an explanation for that in morphology?”

Source:nytimes.com