The diverse tapestry of human faces features an incredible range of nasal shapes and sizes. The form of the nose, a highly noticeable feature, is the result of intricate biological processes shaped by both individual heredity and environmental forces. Understanding why a nose appears flat or broad requires looking into the specific anatomy, the genetic codes passed down through generations, and the history of human adaptation.
Understanding Nasal Structure
The visible shape of the nose is fundamentally defined by a supportive framework composed of bone and cartilage. The upper third, known as the bony vault, consists of the nasal bones that connect to the face between the eyes, forming the nasal root and the beginning of the bridge. The lower two-thirds are primarily composed of cartilage, which is more flexible and influences the overall contour. The septal cartilage runs down the midline, providing central support and contributing to the height of the nasal bridge, or dorsum. Flatter or broader noses exhibit a lower nasal bridge height—less projection from the face—and often a wider breadth across the nostrils, which is shaped by the lower lateral cartilages.
The Influence of Genetics and Inheritance
Nose shape is highly heritable, meaning the specific form is largely dictated by genetic information inherited from one’s parents. This inheritance explains why particular nasal features tend to run consistently within family lines. Scientists have identified specific genes that control the growth of the underlying bone and cartilage structure.
The gene RUNX2, for instance, influences the width of the nasal bridge by regulating bone growth in that area. Other genes, such as DCHS2, GLI3, and PAX1, are involved in cartilage development, affecting the nose tip and the overall breadth of the nostrils. Variations in these genes determine the final size and placement of the skeletal components, directly influencing whether a nose will have a higher bridge or a broader base.
Evolutionary Adaptation to Climate
Beyond individual genetics, the distribution of nose shapes across human populations is a result of evolutionary adaptation to local climates. This idea, sometimes called Thomson’s Rule, links nasal morphology to environmental conditions, particularly temperature and humidity. The primary function of the nose, beyond smell, is to warm and moisten inhaled air before it reaches the lungs.
In colder, drier climates, narrower nasal passages are advantageous because they increase surface area contact, making the air warmer and more humidified. Conversely, in hot and humid climates, the air requires less conditioning, and wider, flatter noses allow for easier, less restricted airflow. Natural selection, acting over tens of thousands of years, favored certain nasal structures in different geographic regions. Studies using 3D facial imaging show a strong correlation between nostril width and local temperature and absolute humidity.
Acquired Changes from Trauma or Development
While genetics and evolution set the blueprint, the final shape of the nose can be altered by external factors, particularly physical trauma and developmental issues. Since the nose is a prominent and exposed facial feature, it is susceptible to injury that can permanently change its structure. A direct impact, especially during childhood when the cartilage is still developing, can fracture or displace the nasal bones or the central septum. If a fracture or displacement of the bone and cartilage is not addressed, it can lead to a long-term deformation of the nasal pyramid. This can result in a flatter, more depressed appearance, sometimes referred to as a saddle nose deformity, where the nasal bridge collapses.