Why do zebras have stripes?


An article asks why biology students have misconceptions about science, and it clears up one misconception while implying another. Cool!

Here’s their example of a common error of thinking:

Zebras developed stripes to avoid predators.

That error is incredibly common: it’s the problem of thinking teleologically. Stripes didn’t evolve for a specific goal. The interesting point in the article is that biology students are just as likely to have these misconceptions as non-biology students, but that they are better at arguing for the teleological fallacy, which suggests that biology education is reinforcing the misconceptions. Uh-oh.

But I have to point out that the educators discussing this problem went on to reinforce another misconception, that the stripes are adaptive.

Thinking that zebras got stripes to dodge predators, Coley says, is an example of a misconception arising from a particular type of intuitive thinking: Our minds automatically attribute cause and effect to phenomena or events, even when there might be none.

But evolution doesn’t involve “forward thinking,” or intention—ancestral zebras didn’t sprout stripes to blend in with their surroundings. Rather, given a population of zebra-like animals varying in stripedness, those with abundant verticals had a selective advantage over their plainer relatives: Hence, they were more successful at reproducing, and over time, the stripes prevailed.

Huh. Did you know that there isn’t any good evidence that the stripes give a selective advantage in camouflage? Sure, there are good examples of disruptive color patterns making it difficult for humans to discriminate them against certain backgrounds, but the question is whether zebras with stripes were better able to survive than zebras without. Here’s a paper that says the large predators of zebras don’t care about the stripes.

The century-old idea that stripes make zebras cryptic to large carnivores has never been examined systematically. We evaluated this hypothesis by passing digital images of zebras through species-specific spatial and colour filters to simulate their appearance for the visual systems of zebras’ primary predators and zebras themselves. We also measured stripe widths and luminance contrast to estimate the maximum distances from which lions, spotted hyaenas, and zebras can resolve stripes. We found that beyond ca. 50 m (daylight) and 30 m (twilight) zebra stripes are difficult for the estimated visual systems of large carnivores to resolve, but not humans. On moonless nights, stripes are difficult for all species to resolve beyond ca. 9 m. In open treeless habitats where zebras spend most time, zebras are as clearly identified by the lion visual system as are similar-sized ungulates, suggesting that stripes cannot confer crypsis by disrupting the zebra’s outline. Stripes confer a minor advantage over solid pelage in masking body shape in woodlands, but the effect is stronger for humans than for predators. Zebras appear to be less able than humans to resolve stripes although they are better than their chief predators. In conclusion, compared to the uniform pelage of other sympatric herbivores it appears highly unlikely that stripes are a form of anti-predator camouflage.

We always just assumed that they must have a purpose, which is another fundamental misconception.

It’s also possible that they might provide an unexpected selective advantage. Here’s another paper that rejects many familiar assumptions about zebras.

Despite over a century of interest, the function of zebra stripes has never been examined systematically. Here we match variation in striping of equid species and subspecies to geographic range overlap of environmental variables in multifactor models controlling for phylogeny to simultaneously test the five major explanations for this infamous colouration. For subspecies, there are significant associations between our proxy for tabanid biting fly annoyance and most striping measures (facial and neck stripe number, flank and rump striping, leg stripe intensity and shadow striping), and between belly stripe number and tsetse fly distribution, several of which are replicated at the species level. Conversely, there is no consistent support for camouflage, predator avoidance, heat management or social interaction hypotheses. Susceptibility to ectoparasite attack is discussed in relation to short coat hair, disease transmission and blood loss. A solution to the riddle of zebra stripes, discussed by Wallace and Darwin, is at hand.

That concluding sentence is probably too optimistic. What they have is a biogeography argument by correlation: stripy equiids are found in areas with serious problems with tse-tse fly infestations. Not explained is why small biting flies would avoid stripes (they cite a 1930 paper that says they avoid striped surfaces, but I don’t have access to it, and they do show some data that flies avoid landing on narrow stripes), or why stripes aren’t ubiquitous in other victims of flies. I think it ignores the fact, though, that short-lived, numerous flies are going to be more subject to natural selection, so wouldn’t a mutant fly without stripe aversion thrive in an area with lots of stripey meals walking around? It’s plausible, though, and I can believe that the biggest misery in the day-to-day live of a zebra is not getting chased by lions, but having to deal with clouds of parasites.

So it’s safe to say “zebras developed stripes to avoid predators” is completely false in multiple ways. It’s better, but still probably wrong, to say “zebras with stripes were less likely to be eaten by predators, and so left more progeny in the next generation”. It’s more likely that “zebras with stripes were less afflicted by biting parasites, and so left more progeny in the next generation”.

Not considered yet is the explanation that “equiid skin patterning mechanisms make expression of stripes relatively easy, and chance variation in pigmentation will produce species that differ in their degree of stripeyness.”


  1. Dunc says

    I think it ignores the fact, though, that short-lived, numerous flies are going to be more subject to natural selection, so wouldn’t a mutant fly without stripe aversion thrive in an area with lots of stripey meals walking around?

    Depends on why they have stripe aversion in the first place…

  2. Doubting Thomas says

    Well, there goes the easy answer. I wonder how this thinking has application to adaptive coloration in general? Leopard spots? Chameleon and Octopus color changing?

  3. says

    Making conclusion about possible past selection pressures based on current ones is a little dubious. Especially in a “Red Queen” situation such as predator/prey or parasite/host. So I wouldn’t discount the predation avoidance model (nor would I advocate it) simply because modern predators aren’t fooled. The parasite model for stripes at least has some positive evidence. As to why the tse-tse flies haven’t adapted, are zebras actually a large enough portion of their “diet” that adapting to the stripes would confer much of an advantage?

  4. says

    Yeah, why don’t octopuses have zebra stripes (well, some do). Why don’t zebras have dynamic pigment cells that allow them to change color and pattern?

    I think it’s important to realize that “adaptation” is not the answer to all differences.

  5. says

    Zebras have stripes because when Noah summoned them they were actually horses. Of course, only two horses were allowed on the Ark, so the others had to think of something else. Two of the were particularly clever and put on their pyjamas. Tricking Noah like this they went on the Ark and were saved from the flood. But since god is only fooled by pasta* and not pyjamas he found out and cursed the horses so the stripes would become permanent

    *German Maultaschen. Cover your meat filling with pasta and god won’t notice that you’re eating meat during lent.

    IIRC the Naturkundemuseum in Berlin claims that they serve as a protection against TseTse flies. I know that nowadays horse owners paint their animals with stripes to discourage nasty insects.

  6. says

    Zebras have stripes because unicorns got to pick first. No studies have been done on the camouflaging qualities of unicorn horns but it must work well. Have you ever seen a unicorn? Didn’t think so.

  7. rietpluim says

    Which proves that unicorn camouflage didn’t work so well after all. Zebras are next on the predators’ list.

  8. jacobletoile says

    I am not so sure after reading that paper that the authors had much understanding of the process of predation, or camouflage. I will admit to not being proficient in reading papers like this. I have a tendency to skim and miss stuff so if I have made an obvious oversight please let me know. Most of the predation I have seen on large groups of prey has been raptors in person and nature programs, but they are consistent enough for me to extrapolate. In a large group the individual is not hiding among the landscape, but among its compatriots. The first task, and a very substantial one is for the predator to identify one individual and separate that individual from the group. This happens at fairly close range and so the drop off in strip resolution over distance is not as significant. The other question I have looking at the paper, camouflage doesn’t work if all the details are resolved well. The whole point of camouflage is to break up the mass being hidden. To do this you don’t want to be able to resolve the detail on the mass being hidden. You want some parts of the mass to be match the background and some parts not to match and the distinction to be fuzzy. While the authors did address how particular predators may view zebras in particular situations, I don’t see those situations as being the ones appropriate to predation. But I may have missed something big

  9. says

    Putting aside the question of whether the stripes really are adaptive, I think a lot of biologists will use teleological language in conversation, and even lectures, as a convenient shorthand. It’s just easy to say “X evolved to accomplish Y.” They know it isn’t accurate, it’s just a way people talk. So I wouldn’t worry too much about the students.

  10. Sastra says

    Stripes confer a minor advantage over solid pelage in masking body shape in woodlands, but the effect is stronger for humans than for predators.

    To echo D’s objection in #4, my understanding is that a teeny tiny advantage at some point in the past might be sufficient to select a species-wide characteristic which later on becomes more or less useless. Couldn’t an advantage in ‘discerning body shape in woodlands’ have shaped the predators? Arms race, etc.

  11. Dreaming of an Atheistic Newtopia says

    I always thought it was very suspicious that if having striped bodied was so great, then those equid species with only striped feet were a problem. Why have stripes in the only part of your anatomy that is hidden from predators?

    As it’s so often the case, this is probably a case for Drift. Influenced in small ways by multiple sources of moderate selection, but yeah, mostly drift…

  12. cmutter says

    An episode of “Nature” from a week or two ago had a different explanation for zebra stripes: dynamic camouflage. I don’t know enough to validate the research, but they showed that the stripes could confuse predators into thinking the zebras were running in the other direction, causing a bit of hesitation in the predator, helping the zebras get away.

  13. says

    This is highly relevant. Quaggas, an extinct sub-species of zebra, had stripes only the front half. These people have used selective breeding to get similar looking animals. While we debate the merits of that, the point is you had perfectly good zebras with unstriped tushies. (They left the stern untoned, as it were.) The animals were exterminated by European hunters, btw.

  14. Gunnar Mikalsen Kvifte says

    There are multiple independent behavioural experiments with tsetse suggesting that they are attracted to large unicolorous surfaces. Some of the papers are relatively recent, including doi: 10.1242/jeb.065540 and DOI: 10.1111/j.1365-3032.1992.tb01191.x

    But, as you rightly point out, the situation is too complicated for a simple adaptionist explanation. There is a nice review at DOI: 10.1046/j.1365-2907.2002.00108.x

    Sorry about the paywalls

  15. robinjohnson says

    I always read things like “Zebras evolved stripes to avoid predators” as less a teleological fallacy and more a sort of shorthand for “Zebras evolved stripes because stripes help them avoid predators and therefore the striped ones had a selective advantage” (whether or not that’s actually right.)

  16. Rob Grigjanis says

    cmutter @14: The linked Nature article addresses this. See page 7, the paragraph beginning with

    Predation has been the predominant factor included in a
    number of hypotheses for body striping in equids centering on
    avoiding predation through confusing predators…

  17. Owlmirror says

    Heh. I just checked Google Scholar for one of the DOIs @#18 above, and noticed this glaring hit (which resulted because it referenced the DOI):

      • How the zebra got its stripes: a problem with too many solutions

    The adaptive significance of zebra stripes has thus far eluded understanding. Many explanations have been suggested, including social cohesion, thermoregulation, predation evasion and avoidance of biting flies. […] In contrast to recent findings, we found no evidence that striping may have evolved to escape predators or avoid biting flies. Instead, we found that temperature successfully predicts a substantial amount of the stripe pattern variation observed in plains zebra. As this association between striping and temperature may be indicative of multiple biological processes, we suggest that the selective agents driving zebra striping are probably multifarious and complex.

  18. ChasCPeterson says

    Jeez, go full-on Moran why don’t you. He’s at least got an excuse: he’s a biochemist and thinks that evolution is all about nucleotides, period, neither knowing nor caring much about organisms and ecology.
    One thing we can say with certainty is that these obvious, high-contrast patterns are phenotypes that are exposed to natural selection. It boggles the mind to think that they are just random, drift-induced whimsies with no effect whatsoever on the biology (probabilities of survival and reproduction) of their bearers. I have no problem whatsoever with the assumption that they are somehow adaptive. As anyone who knows anything about animals knows, however, that’s a very difficult assumption to test rigorously. But that inconvenient fact does not support a chance/drift hypothesis.

  19. busterggi says

    Zebras have stripes because the vegitation around them when they mate acts like a fence and induces strips, just as it does for goats.

    Genesis 30:37-39English Standard Version (ESV)

    37 Then Jacob took fresh sticks of poplar and almond and plane trees, and peeled white streaks in them, exposing the white of the sticks. 38 He set the sticks that he had peeled in front of the flocks in the troughs, that is, the watering places, where the flocks came to drink. And since they bred when they came to drink, 39 the flocks bred in front of the sticks and so the flocks brought forth striped, speckled, and spotted.

  20. says

    I’m ensaddened by how little thought is given to “because stripes are cool.” Who wouldn’t want to mate with someone who has awesome natural stripes?

  21. zetopan says

    Of course zebras developed stripes to hide. That must also be the reason why reticulated giraffes have spots which hide them so very well. There could be some in my house even now but I can’t see them.

  22. monad says

    @19 robinjohnson:
    I thought so too. Teleology may be a fallacy, but isn’t teleonomy supposed to sometimes give functionally similar results?

  23. microraptor says

    Zebras have stripes because they were once preyed upon by a giant zebra-hunting falcon. The stripes confused the falcon while it was flying at height and made it difficult to target individual zebras when it dove. This defensive strategy was so successful that the falcons were driven completely extinct due to being unable to change their diets to stripeless prey like gnus and buffalo.

  24. mithrandir says

    @26, to be honest, sexual selection is as good a hypothesis as any, and once stripiness became fixed in the zebra population, it could easily play at least as much a role in the persistence of stripiness as any external adaptive advantage or lack thereof.

    Even that hypothesis would need to be tested, of course. Just because the stripes are a prominent feature of zebras to us doesn’t mean they’re a prominent feature to zebras.

  25. numerobis says

    I’d never heard the large-animal predation claim; I grew up with the tsetse fly explanation.

  26. mithrandir says

    And now that I think of it, that means even @1 is a viable hypothesis! If restated as “zebras have stripes so that they can tell whether a potential mate is another zebra or just a horse”.

  27. says

    So it’s safe to say “zebras developed stripes to avoid predators” is completely false in multiple ways. […] It’s more likely that “zebras with stripes were less afflicted by biting parasites,

    So, parasites aren’t considered predators?

  28. blf says

    The mildly deranged penguin says zebra stripes are horses’s best understanding of how to wear a really cool natural tuxedo.

  29. Brother Ogvorbis, Fully Defenestrated Emperor of Steam, Fire and Absurdity says

    Racing stripes.

    Seriously. We all know that putting strips down the lateral or dorsal longitudinal axis of an automobile makes it go faster. Upwards of 200 to 300 kilometres per hour. So the zebras decided they needed to go faster and added the stripes. (flamey graphics also work)

    Unfortunately, zebras are, compared to motor vehicles, quite slow. Like, slower than a 1969 VW Microbus. I have seen stripes on a Microbus. They were vertical. Because Microbuses are slow. Additionally, I have seen flames on a Microbus. They were also vertical.

    So the stripes are an attempt to go faster. If they manage to break 200kmh, they will become longitudinal, rather than vertical, stripes.

    See? Easy.


    My assumption was that it was sex-based selection. The predator/prey relationship always struck me as putting the cart before the horse. Er, the zebra.

  30. Brother Ogvorbis, Fully Defenestrated Emperor of Steam, Fire and Absurdity says

    DonDueed @38:

    I want to know why zebras were never domesticated.

    Young zebras tend to be docile and fairly easy to train. Once sexual maturity sets in, they get evil. One of my brother-in-law’s friends has worked in zoos for about twenty years. His nickname if Frodo. But it was a zebra, not Gollum, not a tiger, leopard, lion, jackal, hyena, puma, water buffalo, or hippo that took his finger. It was a zebra. He has had ribs broken multiple times by zebras. He had a kneecap broken by a zebra. They bite and kick and make horses look like the docile sheeple they want us to believe that they are.

    Not sure why zebras become so ornery. But they have a real reputation for it in zoos. I have heard the claim (not sure from where (may have been a conversation at the National Zoo)) that zebras are the most dangerous animals in zoos. Well, zebras and cassowaries.

  31. blf says

    Not sure why zebras become so ornery.

    The popular(?) hypothesis — Jared Diamond even used this is Guns, Germs, and Steel — is it’s an evolved defensive measure. Zebras have excellent peripheral vision and can kill with their kicks, and are known to have killed lions (besides breaking lions’s jaws and similar). They also, apparently, kick with both hind legs at once.

    That is, they are nasty with hair-trigger aggression, otherwise they get ate.

  32. Menyambal says

    I want to add to the folks pointing out that the background for zebra “camouflage” is other zebras. If a lioness charges at a milling herd, it’s really hard to tell where one zebra ends and another begins – it’s just a mass of flickering stripes. And all the clutter on each zebra makes it hard to pick a single characteristic to remember it by – if a cheetah has one zebra singled out and worn down, and that zebra gets back in the herd, well, which one is it?

    For more on the confusingness of bold patterns, look up “dazzle camouflage”. Some WWI ships were painted in Cubist zebra stripes.

    The black and white stripes blur into grey with distance, I think. Up close, for a four-legged predator, the background for a single zebra would be the sky, not so much the grass and ground, or at least the horizon.

    All of which only had to work for a while, if at all. Once zebras started liking the look of stripes on each other, sexual selection would run it to extremes.

  33. Ichthyic says

    Problems testing hypotheses regarding animal colorations like the zebra were exactly the same as those I faced in trying to address why some species exhibit ontogenetic color changes, and others don’t, even congeners.

    It is remarkably hard to eliminate drift hypotheses (especially since most species still have really poor levels of information about genetic relatedness), and I too ran into serious difficulty in finding support for most other hypotheses. In fact, my published work pretty much was a series of experiments that rejected all the extant hypotheses… oddly excepting the very one now rejected for zebras… cyrpsis. The only reason I could not reject crypsis was because we did not have sufficient technology (or resources) at the time to really test the visual systems of potential predators. That has changed a bit over the last 20 years or so.

    For those interested in seeing another lab working on this phenomenon, from the perspective of examining the visual acuity and pattern recognition of the potential predators involved in various hypotheses of crypsis, I would recommend checking out John Endler’s work, and that of his students for the last 15 years or so.

    I think he’s at Deakin University these days.

    There is still a LOT of room for further research in these areas; a lot of it very interesting and useful from the perspective of adding to our knowledge of evolutionary biology.

  34. Ichthyic says

    So, parasites aren’t considered predators?

    not in the strict sense, no. Predators are typically defined as animals that have behaviors that required the death and consumption of another animal.

    parasites, otoh, have behaviors that typically take little resources individually from another animal, and do not directly contribute to its death.

  35. Ichthyic says

    to be honest, sexual selection is as good a hypothesis as any

    not so much. if sexual selection were active wrt to stripe patterns in any given zebra population, we would expect to see much more variation in stripe size, pattern, etc.

    at best, you would have to use a historical assumption that sexual selection might have been a factor that drove a specific pattern to fixation at some point in time. but then, you cannot distinguish that hypothesis from it being the result of fixation through drift.

    to the best of my knowledge, there is no conclusive evidence to indicate mate choice is driven by stripe patterns in zebras. But then, to really test this thoroughly would require vast resources not usually available for such studies. Hell, studying mate choice in captive bred cichlids was hard enough!

  36. Ichthyic says

    ….I’m quite surprised PZ did not jump on the most obvious analogy….

    Why do zebraFISH have stripes?

    because there, you run into EXACTLY the very same questions and issues.

  37. serena says

    I’m pulling this idea directly from my rear-end and admit I’m just a medical-assistant college dropout, but as a resident of a very hot desert (Arizona) it occurs to me (probably naively) that the stark black & white in thin stripe configuration might have some effect on heat absorption. All-black would be dreadfully hot, all-white would be too conspicuous.
    Obvious flaw in my idea: it says nothing of selection; “it’s too hot” isn’t really an evolutionary force especially in an environment the species is already clearly thriving in alongside non-striped species. If heat regulation were that crucial to reproduction, every animal on the savannah would have it.
    So I’ve already talked myself out of this idea, hah; but I still think a striped pelt would both deflect heat in the day and retain heat at night better.

  38. Ichthyic says

    that the stark black & white in thin stripe configuration might have some effect on heat absorption.

    you are not the only one to have come up with this idea. if you look upthread, I think someone even linked to a recent study testing the hypothesis of thermoregulation.

    remember though… if you postulate that thermoregulation is involved in stripes, you also have to answer… why not stripes for all similar animals in similar habitats/situations?

  39. Ichthyic says

    …ah, I didn’t read far enough! I see you already did think of this.

    you’d make a good scientist, from what I can see!

  40. Ichthyic says

    OTOH… don’t talk yourself out of the idea too quickly; remember also that there is lot to the answer of “why NOT stripes?”

    at least as much as to answer the question of “why stripes?”

    for example, animal species are just that… species; isolated from each other to a greater or lesser extent. just because a trait runs to fixation in the populations of one species in a given area, does not mean that the same factors will cause a similar trait to run to fixation in population of an entirely different species. Genetics are complicated, to put it succinctly, and there could be myriad factors at play in why a particular trait runs to fixation in one population vs another; could be linkage, for example.

    so, don’t reject your hypothesis *just* because you don’t see it in other species; but instead use that as a launching point for asking yet another why question. :)

    yeah, science is like that…. it ends up being a nearly endless progression of why questions, which inevitably produce interesting information.

  41. serena says

    Thanks for the feedback Ichthyic; I admit I also didn’t read far enough to see it was mentioned already. While I’ve decided to reject the idea that stripes = thermo-regulation = selection specifically in zebras, the concept might be useful in unrelated application such as landscaping and architecture. All of which are out of my realm of expertise, but yay for ideas!

  42. says

    What genetic and epigenetic factors affect the development of stripes. Are they like calico cats where one colour pattern comes from the father, the other from the mother? Although in the case of calico cats only females have the calico pattern. The same question can also be asked about tigers and for that matter any other animal with stripes.

  43. Ichthyic says

    , the concept might be useful in unrelated application such as landscaping and architecture.

    I had not even considered that. nice lateral thinking there!

  44. Ichthyic says

    Although in the case of calico cats only females have the calico pattern.

    IIRC, that’s not because there are no genetically calico males. it’s because the genes the calico trait is linked to cause death in males.

    I’d have to google to refresh my memory on that though, and with no time left for today, maybe you could give it a shot instead?

  45. Tethys says

    calico coat color is a result of x chromosomes being inactivated, so all calico cats are female. I’m pretty sure PZ wrote an entire blog post on the topic.

  46. serena says

    Thinking further on your “why do/why not do” question; this is actually something that I’ve been curious about for a long time: we can (seem to) explain the “markings” on quite a lot of animals (those that we can identify as having social/mating uses, such as in the feathers and crests of birds or the colors and designs of insects) and we explain a lot of marking styles as camouflage but neither of those things seem to fully explain the why-and-which-how of (especially individual species’) markings.
    I reckon a better understanding of genetics would help me with that. And an ability to accept that not everything needs a “why” that goes further than “this is something that didn’t hamper the species’ ability to perpetuate itself”. What little I do understand regarding predatory vision and color/shape resolution, being able to perceive movement is considerably more important than being able to perceive color or detail, so it’s still somewhat baffling as to why a specific detail (such as the crisp, stark B&W stripes of a zebra) bothers to be.
    The African Buffalo is nearly all-black, typically fattier and larger than zebra, and shares the same environment with zebra. Why does it not have stripes? Whatever those zebra stripes -do- do, the buffalo doesn’t need it. So what does a zebra do that a buffalo doesn’t do?*

    *disclaimer: I’m not actually expecting anyone to have an answer for that, I’m just talking out loud and probably should go do that on my blog instead, hah.

  47. Ichthyic says

    calico coat color is a result of x chromosomes being inactivated, so all calico cats are female.

    that does not sound at all right to me.

  48. astro says

    do we have any idea how long zebras have had their stripes?

    maybe it is thermoregulation, but we haven’t seen it in other animals because it stripes only recently emerged. or maybe only equids (is that a word?) have the right set of genes that allow for the emergence of black and white stripes.

    if it’s sex selection, maybe stripyness has been around just long enough for species identification, but not long enough for zebras to start making mating choices based on particular striping patterns.

  49. Ichthyic says

    but calicoism is not at all a case of ” x chromosomes being inactivated” which makes no sense anyway.


  50. says

    How do zebras blend in at night? Maybe their camouflage is less effective in bright sunlight because during the daylight hours the zebra is operational and able to run?

    Camouflage is going to evolve to be most effective for when the animal needs it most; it might look ridiculous at other times.

    I got a clue about this the other day when a coyote crossed my yard on its way down to the pond to get a drink and maybe try for a turkey. Its orangy/tawn colors were perfect in the orangy/tawn dried weeds and snow. When it stopped moving I couldn’t see it without effort. Maybe winter snow/dry scrub is the hardest time to hunt; the time the coyote most needs to blend in?

  51. Tethys says

    to quote PZ

    The most common example is X-chromosome inactivation in women. Women have two X-chromosomes, but men only have one; to maintain parity in the regulation of expression of X-linked genes, women completely shut down one X. Which one is shut down is entirely random. That means, of course, that all women are mosaic, with different X-chromosomes shut down in different cells.

    So I don’t know why that doesn’t make sense to you Ichthyic, as I know you are quite knowledgeable about X chromosome inactivation.

  52. serena says

    @Marcus Ranum
    Some animals even change the color of their coats and plumage depending on the season, and you may be on to something because I get the general impression that those species which do this (some foxes and hares I think?) seem to base it on the leanest seasons. Like, I don’t know which is more difficult for a given organism to create and maintain: a perfectly snowy white coat or a mottled muted earth-colored coat. If it takes more energy one way or the other, that could imply it’s more “important” to a given animal to protect itself harder (with, for example, camouflage) during a certain season.
    I’m not sure how this hypothesis applies to zebras, who don’t (as far as I know?) change their markings once they’re mature.

  53. Menyambal says

    There may have been another cousin species similar to zebras, back in the long ago. When they split, zebras happened to be a bit more stripey, the cousins were less so. The contrast became a species identifier, got locked in through sexual selection, and now is only non-detrimental in the current environment. Stripes perhaps don’t hurt anything, they don’t have to help.

  54. says

    So, tigers. Why do they have stripes? Different environment to zebras, different mode of living to zebras, relatives have spots or plain coats.

  55. eveningchaos says

    I brought this issue up with regards to an article on CBC’s website and commented on the forum. It was timely that PZ mentioned this important distinction in explaining evolution.


    Of course the thread I started degenerated into a battle of ID vs. scientific evolution and I think this mistake only plays into the hands of ID supporters. Some people still see this qualm as splitting hairs or quibbling over semantics.

  56. Igneous Rick says

    “Why do zebras have stripes?”

    To get to the other side. No, wait. That is a zebra crossing.

  57. vole says

    @38 Never domesticated? Try an image search for “zebra drawn cart” and you’ll get plenty of hits.

  58. astro says

    NelC, i used to wonder about tigers too. and tabby cats. until i saw a tabby cat hunting in low bushes. the stripes do a remarkably good job of camouflage in the shadows.

    so, perhaps zebras are crepuscular hunters? freaky!

  59. microraptor says

    vole @70:

    That’s an example of tamed zebras. For zebras to be domesticated, you’d need to have a captive bred population where any randomly selected individual could be handled with reasonable safety and a lack of fear or aggression towards humans.

  60. randommonster says

    People immediately think “hiding” when it comes to patterns, but I can think of some other interesting aspects that might be interesting to explore:

    – Your fashion forward friends will tell you to wear horizontal stripes to look thinner. Clearly humans have a harder time resolving volume when viewing something in a high contrast dazzle pattern. Maybe big cats have a similar perception challenge. Could make a difference in determining shadows and whether something is turning left or right.
    – Perception of target speed. If you’re a lioness pouncing and you miscalculate that slightly because of the effect of the pattern, maybe that’s a competitive advantage for the zebra.
    – Could there be a group dynamic to a pattern? Meaning, could the dazzle effect be amplified when a mass of similarly striped individuals are moving as a group?
    – Could zebras benefit from just clearly identifying where the mass of the herd is moving? If there’s safety in numbers, maybe there’s a benefit in clearly knowing where the mass of the herd is going?