Studies have found that people whose ancestors come from dry and cold climates tend to be narrower than nostrils, while people from warm and humid climates are usually nostrils wider.

Scholars believe that the possible reason is that for people in dry and cold areas, the narrow nasal cavity can effectively increase the temperature and humidity of the inhaled air and reduce the chance of illness in the upper respiratory tract.
As a result, under the natural selection, the people with wide nasal cavity were slowly eliminated in the dry and cold regions, and the narrow nasal cavity became the mainstream.