The high-contrast pattern of a zebra’s coat presents a classic biological puzzle and often leads to debate about which color is the animal’s true base. Science offers a definitive answer by focusing on the underlying biology of pigment production rather than the fur’s appearance. Understanding this distinction, along with the evolutionary function of the pattern, resolves this question.
The Biological Answer: Skin and Pigment
Biologically, the zebra is considered a black animal with white stripes. This conclusion is based on the color of the skin beneath the hair, which is uniformly black across the entire body. A mammal’s fur color is determined by specialized cells called melanocytes, which produce the pigment melanin.
The black stripes are regions where melanocytes actively produce melanin, giving the hair its dark color. Conversely, in the white stripes, melanocytes are present but signaled to be inactive. The white color is not a separate pigment but merely the absence of pigment, confirming black as the default or ground color.
The Proof in Embryological Development
Further evidence that the zebra is black with white markings comes from its development within the womb. During early fetal growth, the developing zebra is entirely dark, suggesting complete coverage of active melanocytes. As the fetus matures, the distinct striped pattern begins to emerge.
The white stripes form through active inhibition, where a chemical signal (a morphogen) prevents melanocytes in specific areas from producing pigment. This process suppresses melanin production pathways in the cells destined to form the white stripes. Since the default state is for melanocytes to produce dark pigment, the white stripe is an addition to the pattern. The timing of this inhibition influences the width and distribution of the stripes, leading to variations among different zebra species.
Why Zebras Have Stripes
The striking pattern serves several adaptive functions crucial for survival, not merely as a byproduct of pigmentation. One supported theory suggests the stripes evolved primarily to deter biting insects, particularly tsetse flies and horseflies. These pests carry diseases and struggle to land effectively on the high-contrast stripes, which disrupt their visual system upon approach.
The stripes also play a role in thermoregulation, helping the zebra manage the intense African heat. The black stripes absorb sunlight, heating the air above them, while the white stripes reflect light and remain cooler. This differential heating creates small, localized convection currents that help cool the animal’s surface.
A third function relates to confusing predators through motion camouflage and disruption. When a herd of zebras runs together, the mass of moving stripes makes it difficult for a predator, such as a lion, to single out an individual target. This “dazzle” effect prevents the predator from locking onto one animal, hindering the final attack.