Why Do Zebras Have Stripes

A mother zebra with a foal in Tanzania's Tarangire National Park. Credit: Brenda Larison/UCLA

Why do zebras have stripes?

One of nature's fascinating questions is how zebras got their stripes. A team of life scientists led by UCLA's Brenda Larison has found at least part of the answer: The amount and intensity of striping can be best predicted by the temperature of the environment in which zebras live.

In the January cover story of the Royal Society's online journal, Open Science, the researchers make the case that the association between striping and temperature likely points to multiple benefits -- including controlling zebras' body temperature and protecting them from diseases carried by biting flies.

"While past studies have typically focused their search for single mechanisms, we illustrate in this study how the cause of this extraordinary phenomenon is actually likely much more complex than previously appreciated, with temperature playing an important role," said Thomas B. Smith, professor of ecology and evolutionary biology in the UCLA College and senior author of the research.

Larison, a researcher in UCLA's department of ecology and evolutionary biology and the study's lead author, and her colleagues examined the plains zebra, which is the most common of three zebra species and has a wide variety of stripe patterns. On zebras in warmer climes, the stripes are bold and cover the entire body. On others -- particularly those in regions with colder winters such as South Africa and Namibia -- the stripes are fewer in number and are lighter and narrower. In some cases, the legs or other body parts have virtually no striping.

Zebras evolved from horses more than 2 million years ago, biologists have found. Scientists have previously hypothesized that zebras' stripes evolved for one, or a combination of, four main reasons: confusing predators, protecting against disease-carrying insects, controlling body temperature and social cohesion. And while numerous previous studies of the phenomenon focused on a single hypothesis, the Larison-led study was the first to fully test a large set of hypotheses against one another.

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