Ethnicity is defined as the ethnic or cultural origins of an individual's ancestors. Ethnic groups are defined by a shared set of evolutionary features including bone structure, physical characteristics, skin tone and similar traits. Like domestic cats that developed in different geographic regions, these differences are almost entirely surface level, impacting only the appearance of individuals within that ethnic group.
Many of the shared physical traits have an evolutionary basis, rising out of gradual adaptation over time. The pigment of a person's skin is often directly linked to the average number of daylight hours common to the region or geographic area where the person's ancestors lived. This is why people of Caucasian descent are generally characterized by fair skin. This allowed the skin to absorb more of the sun's light, essential for manufacturing certain chemicals within the body, such as vitamin D. Hair texture is another characteristic impacted by these same factors, as the course hair that is characteristic of African people allows for more efficient heat regulation within the body, trapping less of it close to the skin while still providing ample protection from the sun's rays. Ethnicity is simply a means of categorizing these shared traits in a more efficient manner and linking them to a common ancestry.