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Scientists Solve the Mystery of Why Zebras Have Stripes
Hugh Pickens DOT Com (2995471) writes "There have been many explanations for the zebra's impressive stripes including Darwin who thought that the stripes help males and females make sensible choices about whom they mate with. Now Henry Nicholls reports at The Guardian that Tim Caro at the University of California, Davis, has taken a completely original approach, stepping back from one species of zebra and attempting to account for the differences in patterning across different species and subspecies of zebras, horses and asses to see if there is anything about the habitat or ecology of these different equids that hints at the function of stripes. To answer that question, Caro and his colleagues created a detailed map charting the ranges of striped vs. non-striped species and subspecies. Then they worked on a map for the bloodsuckers that targeted those species — specifically, abanid biting flies (horse flies) and tsetse flies.
'I was amazed by our results,' says Caro. 'Again and again, there was greater striping on areas of the body in those parts of the world where there was more annoyance from biting flies.' Where there are tsetse flies, for instance, the equids tend to come in stripes. Where there aren't, they don't. Biologists who buy into the bug-repellent hypothesis say that, all other things being equal, striped animals would have an evolutionary advantage because they wouldn't suffer from the loss of blood, reduced weight gain and lowered milk production that's associated with bug bites. Tsetse flies are also associated with the transmission of diseases. 'There are a lot of them, such as sleeping sickness, equine anemia and equine influenza,' Caro says. Why would zebras evolve to have stripes whereas other hooved mammals did not? The study found that, unlike other African hooved mammals living in the same areas as zebras, zebra hair is shorter than the mouthpart length of biting flies, so zebras may be particularly susceptible to annoyance by biting flies. 'It's clear that the flies can get through that hair and get to the skin.'"
'I was amazed by our results,' says Caro. 'Again and again, there was greater striping on areas of the body in those parts of the world where there was more annoyance from biting flies.' Where there are tsetse flies, for instance, the equids tend to come in stripes. Where there aren't, they don't. Biologists who buy into the bug-repellent hypothesis say that, all other things being equal, striped animals would have an evolutionary advantage because they wouldn't suffer from the loss of blood, reduced weight gain and lowered milk production that's associated with bug bites. Tsetse flies are also associated with the transmission of diseases. 'There are a lot of them, such as sleeping sickness, equine anemia and equine influenza,' Caro says. Why would zebras evolve to have stripes whereas other hooved mammals did not? The study found that, unlike other African hooved mammals living in the same areas as zebras, zebra hair is shorter than the mouthpart length of biting flies, so zebras may be particularly susceptible to annoyance by biting flies. 'It's clear that the flies can get through that hair and get to the skin.'"
So, this is why very few referees suffer from fly bites? I always wondered.
Please Google prior to posting: http://news.sciencemag.org/201...
I want my karma, and I want it now!
You know, if you're going to just copy and paste part of the article as your summary, you might as well post the last paragraph, and get to the actual explanation:
Zebras have stripes because biting flies have an aversion to landing on striped surfaces.
Are Zebras Black with White stripes or White with Black stripes?
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Relevant quotes missing from summary:
"researchers built horse mannequins, painted them in a variety of patterns, coated them with sticky stuff, and found that horseflies seemed to avoid landing on the fake horses that were painted with black and white stripes."
"The proposed explanation was that the flies preferred to land on dark surfaces. Such surfaces reflect the kind of polarized light that reminds the flies of the water or mud where they breed. Light surfaces aren't as attractive, but dark-and-light patterns are even worse — perhaps because such patterns confuse the flies' navigational sense."
The wikipedia article on Zebra's links to the following for a possible explanation to the origin of these stripes:
http://www.bbc.co.uk/nature/16944753
Notice anything similar?
Why zebras always blow big calls at the end of playoff games.
Slashdot insists that I actually type the punchline, a zebra
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I remember reading about it as a kid - that zebra's stripes repel tsetse flies.
Forget where I watched/read it, but I always believed the idea behind the stripes that it was more difficult for predators to single out one zebra.
I thought the stripes broke up the outlines of individuals and made it harder for predators to single one out of a crowd? Or did no actual research go into that claim?
why don't humans evolve this if tse tse flies are so deadly?
Wouldn't it have been easier to "evolve" longer hair?
Other relevant quote:
"Now Henry Nicholls reports at The Guardian that Tim Caro at the University of California, Davis, has taken a completely original approach, stepping back from one species of zebra and attempting to account for the differences in patterning across different species and subspecies of zebras, horses and asses to see if there is anything about the habitat or ecology of these different equids that hints at the function of stripes"
Reading TFA I can conclude that flies prefer biting asses. So, cover yours.
Zebra stripes have traditionally been thought of as an adaptation against detection by vertebrate predators such as lions and hyaenas. A different hypothesis is suggested: that the stripes are an adaptation against visually orienting biting flies and act by obliterating the stimulus presented by a large dark form, which is important in host-finding by many Diptera. This hypothesis is supported by some indirect evidence, and by a field experiment in Zimbabwe in which biting fly catches were compared on moving and stationary black, white and striped models. Striped models caught significantly fewer tsetse (Glossina morsitans) Westwood and other flies (including tabanids) than solid black or white models, but this difference was much reduced in the presence of olfactory attractants.
~Waage, J. K. (1981)
Maybe people studying zebras should start by reading the zebra wikipedia page.
the question here is what first caused strips to appear. what evolutionary pressure created and maintained them first.
as stripless equine species also had predators to deal with but not the flies the flies are the more plausible answer. the effects against predators are therefor likely to be a secondary benefit, and could have caused zebra's to have evolved into forming larger groups then most other animals their size to take advantage of that.
Like why Marketing insists on ruining every useful functional design on the planet...
that would have increased isolation(heat retention), hampering the zebra's ability to run for longer distances, making it more vulnerable to predators and less able to migrate. with the stripes it could keep both at bay.
(for comparison, humans likely lost almost all hair to be able to jog for longer distances then any other creature. allowing us the catch pray through sheer exhaustion under the hot African sun. (our jogging pace is also finely tuned to be the most annoying to outrun, too slow for a sprint, to fast for walking away forcing the creature to keep changing speed increasing exhaustion)
37 Then Jacob took fresh rods of poplar and almond and plane trees, and peeled white stripes in them, exposing the white which was in the rods. 38 He set the rods which he had peeled in front of the flocks in the gutters, even in the watering troughs, where the flocks came to drink; and they mated when they came to drink. 39 So the flocks mated by the rods, and the flocks brought forth striped, speckled, and spotted.
I knew it! I knew people evolved to be annoying!
My sci-fi novel, Ghost Thief, is now available from Amazon.com.
This was stated over two years ago by scientists in Hungary and Sweden.
Why does the title claim this is solved? Even the summary calls it a hypothesis
Please do not title an article as scientists "solved" something, when they merely present a good theory as to why. Sigh...
Zebras evolved to hide from German U-boats
The only thing necessary for evil to triumph is for it to be pitted against a slightly greater evil
Using painted fake horses and sticky glue is does not mimic a real zebra skin that emits sweat & odors. Real skin has subtle temperature variation patterns etc. A badly designed experiment, unwarranted conclusions, not a complete literature study to be aware of other prior explanations, no attempt to design the experiment to bolster the new explanation against existing explanations ...
Will give a B for undergrad project, C for a masters project, D for masters thesis, and an F if it is part of any PhD level work.
sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
Successful mutational adaptations that benefit an organism may do so for multiple reasons, as those mechanisms cannot be known by the DNA, only the effect of the benefits, mutations that successfully accomplish multiple beneficial adaptions will be likely to highly adapt to the population within only a few generations. Similarly multiple overlapping beneficial adaptations will sometimes have compound effects that benefit an organism specifically against one aspect of the environment can evolve independently if each adaption is beneficial enough so as to give the organism an advantage.
Does this mean that the stripes confuse or repel the flies. Is this a visual resistance mechanism?
In Bolivia, Zebras are used to manage traffic in the streets! I even saw a Zebra flash mob in a fried chicken place. A very versitile animal.
Just playing devils advocate (I am sure there is a joke in there somewhere)...
Anyway, as I understand it, evolution is about the selection of traits for survival, This usually involves environment, eating/not getting eaten, and procreation.
It very well could be that Zebra's with their short hair, developed stripes to hide from biting insects, as their survival was significantly impacted enough to warrant the change. While on the insect side of things, perhaps they have enough of a food source that missing out on the Zebra buffet isn't a significant survival issue, and thus never bothered to evolve any eyeballs capable to seeing them for lunch (or perhaps the Zebra evolution isn't all that effective anyway).
What is more interesting to me however, if this explanation is the case, then why didn't Zebra's just evolve longer hair? Then again, I suppose it is hot, so that might not work out so well. Then again not everything has a lot of hair or is striped in those parts either. I am pretty sure evolution isn't really all that exact anyway, which is partially why it takes so damn long to produce changes over generations. I liken it to randomly programming solutions to a problem, some are better than others, but some are pretty good and stick around for quite awhile, or are just good enough, though over time the best solution will get used more often eventually.
Also mixed into the mess is not only physical things like hot/cold, eat/eaten, procreation, but behavior based on those traits. Basically at which point is a stripey Zebra more sexy to another Zebra as that is perceived as better unconsciously. Oh baby, that's nice stripes you got there... I have to think there is also a significant lag time between physical evolution, and behavioral evolution, as the one pretty much has to occur before the other. Perhaps that is the point, if a trait sticks around long enough, it sort of proves itself a bit, which then kicks in the behavior modification, which further reinforces the trait...
Anyway interesting to try and figure it all out, even if only a thought experiment.
I'll be wearing my striped shirts this summer. It's the best defense against mosquitoes!
AFAIK the Waage study did not map the respective habitats of zebras and flies; that is what is actually new in this study, and it supports the Waage hypothesis.
Too bad they didn't evolve longer hair.
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I was told 'Just So' by Rudyard Kipling:
How the Leopard got his spots
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Those stripes are actually some very evolved bar codes. No one would admit that though since it would establish prior art and invalidate all the lucrative bar code patents. :-)
Why would zebras evolve to have stripes whereas other hooved mammals did not?
I don't think that's true. I distinctly remember seeing a shot of a mustang (not the car, the horse) with stripes on its hindquarters. These are wild horses descended from escaped Spanish horses in the western US. I distinctly remember the announcer saying their wild ancestors probably had stripes, and after half a millennium of independent evolution, some were regaining stripes.
According to this link the horses the Blackfeet used often had these stripes. Despite what their legends may say, Native Americans like the Blackfeet got their horses by taming them from this same pool of the descendants of escaped Spanish horses.
Wikipedia does say that the ancestor of the domestic horse, Equus Ferrus Ferrus, often had stripes on its shoulders.
So it sure looks like there's probably some kind of genetic usefulness for stripes in non-domesticated horses, both in ancient Asia and the modern American West as well.
The Onion guys figured this out a long time ago
https://www.youtube.com/watch?...
http://validator.w3.org/check?uri=http%3A%2F%2Fwww.slashdot.org Errors found while checking this document as HTML5!
I remember reading an article on Snopes about this, quite a while ago.
As I understand it, the fly's visual system evolved a beneficial mutation that glitches what they see. Zebras are in reality just black horses (look at their snout), but the fly's retina paints those white stripes on them. This allows the fly to more easily attack the zebra, although not as effectively as if the animal was all white. This effect is well known in our domesticated horses -- horseflies are attracted to light colored animals such as Palominos. Humans are also faked out into thinking there are stripes because we only see zebras on nature documentaries, and a TV cameras have similar scanning artifacts.
That's the way I remember the Snopes article, anyway, and I read it on the Internet so it must be true.
There is nothing new concerning this particular purpose of a zebra's stripes. For example, it has long been debated whether the now-extinct Cape Kwagga was simply a zebra which had been removed from the tsetse belt for long enough.
Causation?
I didn't see where zebra coloring schemes was demonstrated to repel or confuse pests like tsetse flies. Have these scientists demonstrated something about flies vision that the stripes interfere with? Do flies even depend upon vision to locate prey?
I had heard the theory that zebra striping was a kind of dazzle camouflage which confused larger predators when trying to pick out one animal to pursue. I just didn't think flies could see that well.
Have gnu, will travel.
Can't we pay our scientists to research something important to humanity instead of Zebra stripes?
Hey, I know why you're biting me. Cause your mouth is longer than my hair. You don't bite the other guy cause you don't like having to snuggle past his long nasty beard, but you know what? Heard of evolution, B#$!h?!
[Grows a stripe] uh... hmm..
[More stripes...] Still biting? Take, um... that.. yeah land on that line, you bloodsucking bastard!
I seriously thought my hair would just grow longer... wtf evolution?
I recall hearing this theory a short while ago and rolling my eyes at the ridiculous reach of "insect repellent." Goes to show you what a great experiment can reveal. Some of the ideas that natural science types come up with to test hypotheses are as simple and elegant as they are revealing.
I swear to God...I swear to God! That is NOT how you treat your human!
...because they're still covered in flies despite their stripes. Every equine animal is a nasty fly magnet.
Do tigers have stripes for the same reason? If not, how do we know that Zebras don't have them for the same reason as tigers?
no, I don't have a sig
Quote: The study found that, unlike other African hooved mammals living in the same areas as zebras, zebra hair is shorter than the mouthpart length of biting flies, so zebras may be particularly susceptible to annoyance by biting flies. 'It's clear that the flies can get through that hair and get to the skin.'"
So why stripes? Evolving longer hair would have been easier. But that only illustrates that one can explain virtually anything--or its opposite--with Darwinian arguments. An animal gets larger? Darwinian selection. An animal gets smaller? Again, Darwinian selection.
And that means that proving anything is built into the theory itself. "Survival of the fittest" is really "survival of the fittest to survive," with fitness defined solely by survival. It's a bit like claiming the path to becoming rich is to "make more money." It's true but meaningless.
Flies can't land on Zebras because their Arthropod eyes cause them to see Moiré at a certain focal length when they try to land and they don't have a low pass filter and anti-aliasing to battle this issue.
Why would zebras evolve to have stripes whereas other hooved mammals did not? The study found that, unlike other African hooved mammals living in the same areas as zebras, zebra hair is shorter than the mouthpart length of biting flies, so zebras may be particularly susceptible to annoyance by biting flies. 'It's clear that the flies can get through that hair and get to the skin.'"
I don't buy it. So why did the Zebras not just simply evolve longer hair? Seems to me that's a much simpler evolutionary change than stripes.
This more than any other reason is why I'm losing my taste for /. and my faith in humanity.
Polkadots made them look fat, and floral prints are not suitable for the dry season.
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I think the stripes have more to do with regulating the Zebra's body temperature than to deal with flies.
Have you ever done that science experiment in elementary where the black balloon inflates itself when put on the top of a pop bottle, because of the heat absorption?
Where as the white balloon doesn't inflate itself.
Someone needs to take a black and white striped balloon and see if it inflates itself or if it regulates the heat better by acting as a kind of natural painted heat sink.
I have a theory on why the stripes may confuse flies. Compare it to driving in sunlight and then entering a tunnel. Your eyes take a while to adjust to the tunnel's dimmer light, and then have to re-adjust on the way out of the tunnel. When you are fly-sized, you'll have a somewhat similar issue near black and white stripes. The changing light levels may make it hard to identify enough surface details to land properly. When your eyes adjust to the white areas enough to make out hair clumps, you then are in a dark area and your eyes are not ready for dark hair details.
And while it may be possible for insects to evolve better eyes, if zebras are only one of many target animals, then it may not make sense to carry the extra weight and chemistry brewing mechanisms of eye improvements for just one kind of prey. It may keep away generalist insects, reducing the number of fly species that try to munch on your hide.
Table-ized A.I.
There is no proof in PUDDING! The proof of the pudding IS IN THE EATING!
Now, why don't you make like a tree, and get out of here?
So why doesn't this theory apply to Holstein cows? Just because of the stripes vs splotches of black and white?
What does this have to do with global warming?
They did evolve... where do you think lions came from?
I put the 'Physics' in 'Physical Attraction'
Once again those writing this up spout all sorts of rubbish that does little else than give science a bad name.
Scientists made the independent observations that zebras have stripes and flies don't like landing on the stripes. Putting these 2 together "solves the mystery of why zebras" don't get bitten by the flies as much, but it says absolutely nothing at all about "why zebras have stripes".
There has to be some other mechanism involved to create the genes that code for the striping.
Wouldn't it have been easier, from an evolutionary standpoint, for the zerbra to just grow slightly longer thicker hair to keep the flies away like the other animals mentioned?
Why the whole stripes thing?
so i call bs