The nose is one of the most variable features on the human face. The snub nose, a distinct and recognizable form, results from a complex interplay between inherited genes and long-term evolutionary pressures.
Defining the Morphology of Snub Noses
The snub nose, often called a retroussé or button nose, is characterized by specific anatomical features. It is typically shorter in length compared to other common nose shapes. The nasal bridge, the bony and cartilaginous structure that runs down the center of the face, is often less prominent or lower set.
The most defining characteristic is the tip, which is slightly upturned or rotated upward. This upward tilt creates an increased angle between the tip of the nose and the upper lip, known as the nasolabial angle. The rotation may make the nostrils more visible when viewed from the front.
Genetic Inheritance of Nasal Shape
The shape of an individual’s nose is primarily determined by their genetic makeup, which dictates the development of bone and cartilage in the face. Nasal morphology is a highly heritable trait, but it is polygenic, meaning it is controlled by the combined influence of multiple genes rather than a single factor.
Recent genetic studies have identified specific genes associated with different aspects of nasal structure. For instance, the gene RUNX2 influences the width of the nasal bridge by driving bone growth. Other genes, such as GLI3 and PAX1, are linked to cartilage growth and nostril breadth.
The gene DCHS2 specifically influences the degree of projection and the angle of the tip, which directly relates to the upturned characteristic of a snub nose. Because many genes each contribute a small effect, the inheritance of a snub nose follows a non-Mendelian pattern, resulting in a continuous spectrum of shapes.
Evolutionary Adaptation and Geographic Distribution
While genetics determine an individual’s nose shape, the distribution of these shapes across human populations points to evolutionary processes. The primary functional role of the nose is to condition inhaled air, ensuring it is warm and moist before it reaches the lungs.
Theories of evolutionary adaptation link nasal shape to the climate of an ancestral environment, a concept known as Thomson’s Rule. Narrower noses with longer nasal passages are hypothesized to be more effective at warming and humidifying cold, dry air, an advantage in colder climates. Conversely, wider, shorter nasal passages are thought to be less necessary for air conditioning in warm, humid regions.
Research analyzing the width of the nostrils and the base of the nose has shown a correlation with local temperature and absolute humidity. Populations whose ancestors evolved in warmer, more humid climates tend to exhibit wider noses. The prevalence of shorter, less-projecting nasal forms, such as the snub nose, is thus seen as an adaptive trait in specific geographic regions.