Why do zebras have stripes?

UCLA study finds that regulating body temperature may be a key factor

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.

Analyzing zebras at 16 locations in Africa and considering more two dozen environmental factors, the researchers found that temperature was the strongest predictor of zebras’ striping. The finding provides the first evidence that controlling body temperature, or thermoregulation, is the main reason for the stripes and the patterns they form.

Separate research by Daniel Rubenstein, a Princeton University professor of ecology and evolutionary biology and a co-author of the Open Science paper, and Princeton undergraduate Damaris Iriondo strongly suggests that boldly striped zebras have external body temperatures about five degrees Fahrenheit cooler than other animals of the same size — like antelopes — that do not have stripes but live in the same areas. The Rubenstein study is not yet published, but it is cited in the Open Science paper.

Larison has studied many zebras during her field work throughout Africa — including in Kenya, South Africa, Tanzania, Uganda and Zimbabwe. Using the fact that their stripes are unique like fingerprints, she is able to distinguish one zebra from another.

In addition to Rubenstein, arguably the world’s leading expert on zebras, the study’s co-authors were Alec Chan-Golston and Elizabeth Li, former UCLA undergraduates in mathematics; Ryan Harrigan, an assistant adjunct professor in UCLA’s Center for Tropical Research; and Henri Thomassen, a former UCLA postdoctoral scholar and current research associate at the Institute for Evolution and Ecology at Germany’s University of Tübingen.

The research was supported by the National Geographic Society Committee for Research and Exploration.

Larison and her research team have also collected zebra tissue samples and have used cutting-edge technology to sequence zebra DNA to try to identify which genes code for striping. The team is continuing to study the benefits stripes provide.

The material in this press release comes from the originating research organization. Content may be edited for style and length. Want more? Sign up for our daily email.

1 thought on “Why do zebras have stripes?”

  1. Last year another group of researchers did claim `insects` were the reason for Zebras stripes ..Now this one .

    “ the temperature adaptation hypothesis” , let me tell you this out-front `Temperature is everybody’s problem-so to speak- if you have to live and survive in hot`tropics` .

    What it means you have to see `striped animals of all kinds and different species all over the tropics if having stripes had been effective for heat adaptation or one way or other was the reason for Zebras stripes . Clearly it is not the case here we do not see that strategy for too many species with similar circumstances .

    Let me go with “fundamentals” in order to regulate “anything” you have to “change” “synchronized fashion “ the intensity ,the dose UP or DOWN or in-between , in other words if you are BORN WITH FIX amount of stripes and coloration ratio (Color pattern of Zebras stripes unique for each individual and fixed ) , the environmental temperature CHANGES as usual ,daily(night and day) as well as seasonally ..SO how can something (zebras stripes) FIXED UPON BIRTH CAN CHANGE synchronized fashion with the TEMPERATURE CHANGE – Like CHAMELEON .. So the case is closed ..something fixed that can not “change up and down” can NOT REGULATE anything ..This is fundamental ..

    I personally think ; the stripes could give certain `survival advantage` to zebras as a species , like specific social communication in between individuals –mother and baby particularly – to keep them in close proximity to each other without any –sound- or –cry- in complete silence with visual recognition in distance without need smell each other ; distant and immediate recognition with sight –in complete silence- in between mother and baby is –evolutionary survival advantage for the species- not only this form of visual recognition avoids alerting or attracting unnecessary predators but also –increases the bondage and close visual contact at all times between mother and the baby , not being lost easily in any commotion or stampede , it may also help socially to differentiate close relationship in between individuals to –avoid inbreeding- and increase variability for the survival and adaptability of the Zebra species which is genetically -absolutely important – . In other words social recognition and differentiation of individuals easily similar to –fingerprint pattern of stripes recognition unique design upon birth for each individual – . Zebras could have gone through a `bottle neck` in their evolutionary past environment that the reasons I listed above could have given them clear social survival advantage .

    All these reasons has clear survival value for the species and might very well be the actual underlying reasons behind the stripes rather than ` highly questionable` statistical correlation observed in between blood sucking predator insects and stripes of pray Zebras as well as heat adaptation hypothesis claimed in this research .

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