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Why Do Zebras Have Stripes? New Study Offers Strong Evidence

Zebra stripes evolved to keep pesky insects at bay, according to the most thorough study to date on the subject.

All three species of zebra have bold stripes in comparison to other African grazers like buffalo and antelope. This so-called stripe riddle has puzzled scientists—including Darwin—for over a century, leading to five main hypotheses: that the stripes repel insects, provide camouflage, confuse predators, reduce body temperature, or help the animals interact socially. (See “Zebra Stripes Evolved to Repel Bloodsuckers?“)

A photo of zebras in Tanzania.
Zebras watch a photographer in Tanzania’s Serengeti National Park. Photograph by Brian Hilsmeyer, National Geographic Your Shot

For the first time, scientists played all of these theories against each other in a statistical model—and the result was pretty much, well, black and white.

“We found again and again and again [that] the only factor which is highly associated with striping is to ban biting flies,” said study leader Tim Caro, a biologist at the University of California, Davis.

“I was delighted to see the results were so strong in one direction.”

Studying Stripes

For the study, Caro and colleagues collected data from a vast range of sources, including museum collections and historical maps.

First, the team looked at variations in striping patterns across the seven living species of the equid group—which includes horses, asses, and zebras—and their 20 subspecies. Most have some sort of striping somewhere on their bodies.

They also noted where the stripes occurred on the body—for instance, the face, belly, or rump. (See pictures of zebras in National Geographic magazine.)

The team then mapped where current and extinct equid species live, where biting flies are found, the ranges of predators like lions and hyenas, distribution of forests, and other environmental factors that could influence the evolution of stripes. The data was then entered into a statistical model to find out which variable best explains striping. (Download zebra-stripes desktop wallpaper.)

The results showed that the range of striped species overlaps with where biting flies are most active—regardless of species and where the stripes occur on the body, according to the study, published April 1 in the journal Nature Communications.

Not the Last Word?

Brenda Larison, a biologist at the University of California, Los Angeles, who studies stripes in plains zebras, said the new study’s approach is “broad brush,” and that more specific research may be needed. (Related: “Resolving the Riddle of Why the Zebra Has Stripes.”)

That’s why “the story is likely to be much more complex, and this is unlikely to be the last word on the subject,” said Larison, who has received funding from National Geographic Society’s Committee for Research and Exploration.

Though Larison agrees that deterring flies is the “best supported hypothesis to date, most of the other hypotheses aren’t well studied, and there is still a lack of direct evidence,” she said.

“We really need to know what happens with live zebra in the field before we can be sure.”

Scientists haven’t actually observed zebras in the wild to see if biting flies avoid alighting on them, in part because it’s difficult to get that close to the animals. It’s also not known why biting flies steer clear of stripes.

However, study author Caro said he’s confident that biting flies swarming around a mixed group of herbivores would avoid zebras. (Watch a video of competing zebras.)

We’ve “moved the debate to the next stage—we can discount all [the other] hypotheses pretty conclusively,” he said.

Follow Christine Dell’Amore on Twitter and Google+.

Comments

  1. BigDred
    North Carolina
    July 25, 10:16 pm

    The thing to remember here is that this theory was developed using a “statistical model”. There was no actual field data collected. No one observed the zebras and flies to come up with this conclusion. They simply put a bunch of information into MATLAB, and pressed ENTER and copy/pasted the answer.

  2. ernessy
    nigeria
    July 20, 4:29 pm

    I love this place, but some people just can’t afford to leave their stupidity @ home. Nice comments and some very very annoying ones as well. I won’t say anything else but just keep it coming.

  3. Kristen Stout
    Charlotte, NC
    July 14, 8:51 pm

    I have a hypothesis as to why flies would avoid biting striped animals. Is there somewhere I submit it?

  4. William the 1st
    Guildford uk
    May 26, 12:54 am

    I think they are one of the ancient animals, that is why they are black & white, and if you wonder why they are striped, because tigers slaved them for a long certain period of time.
    Legit!.

  5. Duncan
    Rochester, NY
    April 24, 4:09 pm

    Some of the comments are funny. 1) No, it’s not an April Fool’s joke. 2) Biting flies are incredibly good at spreading disease, so they aren’t just a nuisance. 3) If we were divinely created, the Good Lord would have had the sense to give us separate entrances for air to our lungs and food to our stomach. Why have them cross so that we can choke on our food? 4) Like all good research, this is not the final word, and raises as many questions as it answers. 5) Flies are very visual; they do not get around by scent alone. They have big eyes, after all.

  6. coastguy
    Ohio
    April 17, 9:57 am

    The zebra was created when a black horse mated with a
    white horse. It is a biracial animal that lives in
    harmony

  7. Alphonse
    US
    April 14, 1:55 pm

    As METIN GUNDUZ said on the 2nd,
    “Annoyance and nuisance caused by insects are not evolutionary strong motives in any form or shape ; since these factors caused by insects are not linked to the survival of that species if any relationship ever exist between annoyance and survival at all.”
    If the relationship existed, wouldn’t humans be close to extinction in some parts of the world simply due to the fly, gnat, and mosquito annoyance factor?
    Is that “evolutionary gene” in all other non-striped mammals that live alongside the zebra dead?
    Also, why hasn’t the same study been done with another very well-known striped mammal, the tiger?
    I find that the only conclusion to make here, based on everyone’s opinion, is that this is inconclusive.
    And how Human to want to take yet another wild animal and domesticate it just for our pleasure instead of letting it live FREE.
    And let’s keep beauty out of this, unless it’s from a lion’s point of view.
    As in informative article, not so great. As a debate starter among readers? Kudos, but that is more of a facebook thing, not the NatGeo quality reading I expected.

  8. Steve Slater
    Smithfield VA
    April 8, 2:40 pm

    It’s God’s design? Be careful, Mr. Assured. They will toss you out of MENSA if you capitalize God.

  9. John Fleming
    Melbourne, Australia
    April 8, 6:23 am

    Guys, let’s get serious here, note the date the report was released, doesn’t that tell you something ??
    Like all good hoaxes there’s elements of truth but the inner sceptic in me is shouting loud and clear …. April Fools !!

  10. Jerry Saint James
    Colorado Springs
    April 8, 1:41 am

    Then why haven’t other Horse Species done the same thing? They suffer with Horse Flies constantly!

  11. Terrence
    April 7, 9:16 pm

    what’s black white and red?
    .
    .
    .
    a zebra with a sun burn! ooo!

  12. konjuro munir
    Malaysia
    April 7, 6:27 pm

    i think the stripe is very delicous

  13. Dwayne LaGrou
    Lapeer, Michigan
    April 7, 5:46 pm

    And I thought they had stripes so that they could use bar code readers to tell each other apart easier!?
    Sound like as good an answer as any other!
    What do you all think?

  14. Amin
    Nigeria
    April 7, 4:51 pm

    So that man will not mistake it for a beast of burtden or an equestrial animal

  15. Ayanle
    sealth
    April 7, 3:11 pm

    Black and whit strips are 99 and the names of Allah are 99.

  16. Rizal
    Indonesia
    April 7, 2:52 pm

    We could make new discovee that stripe added red by bite compared to smell the dirt too long.

  17. Andre Bevonk
    Cape Town
    April 7, 2:09 pm

    Zebras have stripes so that the wild horses think they wear pajamas and don’t bother them for a quicky.

  18. Lauge
    April 7, 12:30 pm

    So are Zebras black with white stripes or white with black stripes???

  19. Michelle
    Poland
    April 7, 12:04 pm

    Oh god, reading the comments made me laugh real much. Before you get irritated by the article notice the date of submission guys ^^ It was april fools’ National Geo style!

  20. Christine Dell'Amore
    April 7, 11:42 am

    Thanks for the comments everyone! This has sparked a really interesting discussion. For those of you who noticed the water buffalo error, thank you! I’ve corrected it above.

  21. Peter
    NSW, Australia
    April 7, 11:05 am

    Perhaps a comparison against other black and white banded or other contrasting banded animals is in order, such as our bandy bandy snake.

  22. Juan Carlos Díaz Crespo
    Mexicali, B.C. México
    April 7, 9:40 am

    *Aclaración a Rob Johnson & TAM :
    El búfalo de agua de origen asiático también vive actualmente en África, desde hace mucho tiempo fue llevado por el hombre.

  23. Rob Johnson
    Zimbabwe
    April 7, 8:11 am

    The author compares zebra to other African antelope and “water buffalo”. The ONLY Buffalo in Africa are Cape Buffalo. Water Buffalo are indegineous to Asia. Please check your facts before posting a column!

  24. Gashaw
    Cape Town
    April 7, 7:44 am

    Zebras had been domisticated by the Borena tribe from Oromo ethnicity in east Africa. Before stripes emerge zebra was a all-black zebra.

  25. Gunnar
    Iceland
    April 7, 7:07 am

    @METIN GUNDUZ
    It’s a well known fact that the tsetse fly is attracted by the color blue, but doesn’t like to come near the color white. I’ve done many safaris in E-Africa, and I can testify that this is true.
    In the Serengeti there are blue tsetse fly traps all over the place, and they work like a charm. For some reason those flies seem to be drawn to it

    • Christine Dell'Amore
      April 7, 11:44 am

      Interesting, I wonder why it likes blue?

  26. Comadrona
    April 7, 6:27 am

    One of those research questions which makes people wonder about the benefit of research.

  27. henok
    Ethiopia
    April 7, 5:46 am

    how many strips does zebras have? is the numbers equals?

  28. MJ
    NJ
    April 7, 4:46 am

    ‘Cause Zebras are sayin’, “It don’t matter if you’re black or white!” Heehee! haw.

    • Christine Dell'Amore
      April 7, 11:46 am

      Haha, nice!

  29. Tam
    April 7, 4:24 am

    I wasn’t aware that there were Water Buffalo in Africa..

  30. voodoopiles
    UK
    April 7, 4:02 am

    It’s because in the old days when everything was in black and white they were much harder to spot

  31. wattyler23
    England
    April 7, 2:45 am

    Dear Weird and Wild I have said this before and I’ll say it again. The stripes on a Zebra create an interference pattern.
    When Zebras herd together their predators such as Lions can not pick out an individual because of the interference effect. Lions stalk the herd, it creates fear in the herd, they panic and stampede, one or more become separated and alone, the Lions see there chance and pounce, they have to feed themselves and offspring. The stripes are not camouflage

  32. Ebby Abbey
    Nigeria
    April 6, 2:36 am

    good work

  33. Jackie
    Cleveland Ohio
    April 5, 10:20 pm

    I asked our zebra Holly and she suggested that there were better ways to spend time like thinking about like how we as humans could get along better with each other and be more respectful of the natural worls

  34. sena
    turkey, ankara
    April 5, 1:53 pm

    because they have to hide from lions and other wild animals. :)

  35. ted
    sf
    April 5, 10:31 am

    God gave Zebras stripes so humanes would have something to talk about other then sex and violence.

  36. michael r.
    Mi,US
    April 5, 9:02 am

    I agree with many comments on this page however; i want to point out that from my experience in plant horticulture that evolution and de-evolution are always occuring based on bio availability of elements in a given enviroment, and incects generally adapt faster than plants or animals so it is unlikely that a zebra’s stripes are developed as protection it is more likely a reaction from the fly bites or for social interaction. It is true that zebras are black with white stripes since black is an abcence of color and white is a combination of all colors. The more we study this concept the more we will realize that the answer that alludes us can only be found from studying the microscopy of the hair folicle and skin rather than observing the flies and developing a theory based on the predator’s behavior since the number of variables are beyond control at this level. Furthermore- the accepted scientific methods are all based on human preceptions and limited by our five physical senses. In effect we dumb down creation to our limited understandings. We should all agree that the oddity of the zebra pattern is for a reason… why cant it just be for the beauty that God made for us to enjoy?

  37. John
    April 4, 5:43 am

    stupid question, stupid answer

  38. Jinu Nachhyon
    kathmandu,nepal
    April 4, 12:36 am

    i think zebra have their strips from the day of their birth

  39. David Quesenberry
    April 3, 10:24 pm

    One blaring no-no in statistical modeling is the use of a large sampling to denote correlation. A large enough N will always give you a significant p, even if you set your hypothesis to 1-tailed with alpha = .01. As has already been stated before, correlation does not mean causation. They may have deduced a strong positive correlation, but not proven a causality.

  40. Sierra Ross
    Chelsea,OK
    April 3, 8:15 pm

    I belive it is nothing i could ever figure out, i’m not exactly the sharpest tool in the shed.

  41. OYIBO SUNDA
    MAKURDI BENUE NIGERIA
    April 3, 4:54 pm

    i think the stripes on zebras are to the glory God. Permit me to say also that it is a protective coloration against predators. I want the researchers to tell us the original color of zebra.

  42. Ashwin
    India
    April 3, 11:08 am

    May be when Zebras move in a herd they project being a large animal as the stripes make it difficult to distinguish one zebra from another confusing the predator.

  43. Paul Hebner
    New York City
    April 3, 7:54 am

    The problem with this article is that it gives short shrift to any challenge of statistical methodology, which can address questions of coincidence and periodicity, but not cause and effect. No statistical argument is valid without direct evidence to support it. So, statements in the article like “The data was then entered into a statistical model to find out which variable best explains striping.” and “we can discount all [the other] hypotheses pretty conclusively,” are not only categorically false, but dangerously misleading, despite the vaguely qualifying statements the author includes.

    As such, this article does not represent the scientific method and should not have appeared on this website.

  44. CeeCee Hall
    California
    April 3, 6:31 am

    Zebra’s are incrediable creatures. I find them Beautiful.
    I have always wondered why we have not domesticated
    these amazing creatures for riding, like horses?
    <~ would love to ride a Zebra!

  45. Assured
    NV
    April 2, 3:55 pm

    God’s Design! White and black stripes make the zebra easy to spot almost anywhere—especially for hungry lions. So why does it have them? These stripes make it tough for predators (even flies) to target zebras that move in a herd. This dizzying effect is called motion dazzle not evolution. You see the same striped predatory protection markings in other species – fish, birds and reptiles (and they are not affected by flies). It’s God’s design!

  46. George Denniston MD
    United States
    April 2, 3:01 pm

    A study was done several decades ago that took out the white stripes and counted insects landing on the zebra. Fewer landed on the stripes, thus giving the zebra survival value, because of the tsetse fly carrying African Sleeping sickness.

  47. Tyrone
    April 2, 2:06 pm

    Of course, there’s that little issue that correlation does not imply causality to deal with…

  48. Rodant Kappur
    USA
    April 2, 1:48 pm

    April Fool!!
    Zebras don’t really have stripes – it’s an optical illusion.
    You all got suckered in.

  49. Paul Burnett
    April 2, 12:32 pm

    Zebras are black with white stripes: zebra embryos are solid black – the white stripes show up before birth.

  50. Paul Burnett
    San Francisco Bay Area
    April 2, 12:24 pm

    It’s called “Dazzle Camouflage” – lookitup at Wikipedia. The flies can’t find the zebras.

  51. METIN GUNDUZ
    April 2, 8:06 am

    Let me tell you this out-front , no matter what correlation studies they did between zebras stripes and flies carrying parasites in this study it is not convincing at all :
    First the flies find their target with scent , heat (temperature generated by the target animal) and CO2 in other words mostly with chemical cues from their target mostly warm blooded animals for blood sucking purposes rather than visual , why should fly be fooled easily by the color ? or the pattern of the stripes , that is absolutely absurd ; simply because it ignores the – evolutionary flexibility and variability of insect populating – in other words insects can easily develop variants which are completely color blind or indifferent to the patterns of zebras too , no matter what color or stripe pattern they may have .
    Second what specific killer disease Zebras getting from these flies so the number of bites or no bites might give survival advantage to the zebras . Even stripes lower the frequency and number of bites it can not lower to `zero bites ` from insects in any way or form , so there is no guarantees for protection from flies or deadly diseases since no way of knowing which specific individual fly carrying the deadly parasite –it is like playing like Russian Roulette with the disease – which would bite the unlucky Zebra .
    Annoyance and nuisance caused by insects are not evolutionary strong motives in any form or shape ; since these factors caused by insects are not linked to the survival of that species if any relationship ever exist between annoyance and survival at all .
    Lowering the number of insect bites itself is not guaranteed protection against deadly disease in any circumstance …Evolutionary `correlation studies not necessarily give the actual clue for the evolutionary motive behind the stripes of zebras . Correlation might turn out to be simple unrelated `coincidences` with no cause and effect relationship at all . Statistical studies of todays word particularly for the –geographic distribution or habitat of insects in a given environment can not be assumed to existed same way for the millions of years back in time , insect habitat might have been different than ; so there could be no link or correlation with stripes in the past …
    Blood sucking insects are so widespread in Africa changing `stripe pattern` for protection from them forever as a evolutionary strategy is too simplistic , if it was effective we would have seen –striped animals all over the world- to protect themselves against the blood sucking insects – Including Human beings would have had –stripes like Zebras- for protection against biggest parasite (malaria ) carrier and killer of mankind the notorious mosquitos for the analogy …
    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 – . 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 .

  52. hussain
    Egypt
    April 1, 8:11 pm

    evolution!
    again and again!
    when will the so-called scientists give up this theory..?

  53. john
    tutuilla
    April 1, 7:30 pm

    When they are in a herd, an individual can’t be picked out.

  54. Sally Wells
    Los Angeles, CA.
    April 1, 7:26 pm

    Nat Geo should know better with titles like: Zebra stripes evolved to keep pesky insects at bay,…

    Stripey fur evolved and the stripes had the useful effect of warding off flies, which turned out to be a useful adaptation, and more of that type survived to reproduce. Voila, no ID creator required.

  55. Richard W. Green
    Boston
    April 1, 5:58 pm

    The zebra is a black animal with white strips and April fools on us all!

  56. Dale
    Oregon USA
    April 1, 3:35 pm

    Suppose I wanted to study why biting flies are located in varying densities around Africa. If I were to use the methods described in this article, I would find likely find a strong correlation between areas of high densities in flies and high densities in Zebras. I might conclude that biting flies prefer zebras and/or zebra stripes attract the flies. Is there something wrong with my logic? (likely) If not, then what is wrong with this study?

  57. Christine Dell'Amore
    April 1, 2:24 pm

    Hey Michael, yep, it did: “It’s also not known why biting flies steer clear of stripes.”

  58. Cairagan
    Vermot, USA
    April 1, 2:24 pm

    So, dressing prisoners on a chain gang in striped clothing is the humane thing to do?

  59. Nicholas
    Here
    April 1, 2:10 pm

    What I really want to know is: Are Zebras white with black stripes or Black with white stripes? The research does not address that.

  60. Zeb
    ID
    April 1, 12:20 pm

    Tranquilize two zebras and dye one white and another black. Use a powerful spotting scope to observe fly behavior. I’m guessing flies are not the underlying force that guided natural selection. Many snakes, and fish have bands and stripes and flies are not an issue. I think stripes intimidate predators.. Primitive human cultures use striping paint to appear frightening.

  61. Michael O'Brien
    April 1, 12:16 pm

    Why do biting flies avoid stripes? A scenario:

    Mother fly: Come on, it’s good for you!

    Baby fly: Eeew! Zebra, it’s yucky!

    Sorry–but the article didn’t address that question.