Evolution doesn’t answer to a single why question. Maybe the stripes have been useful to the zebra population’s survival, maybe not – but it is quite clear.that there is no singular reason but a bundle of things. E.g. the stripes make zebras harder to distinguish in a herd, which certainly lead to some percentage of survival. Flies too? Cool! But answering it as if there was some intention behind it? That is not how evolution works.

Evolution doesn’t care and has no sense of meaning, like in genetic algrotihms it is just about which patterns survive, which die and which remain as a funny annecdote with no practical effect.

> the stripes make zebras harder to distinguish in a herd, which certainly lead to some percentage of survival

From the article:

> Amanda Melin of the University of Calgary recently showed that lions and hyenas can’t even make out the stripes unless they get very close.

> unless they get very close

Sounds like it could still influence hunting as the predators have to get very close to make a kill

> But answering it as if there was some intention behind it? That is not how evolution works.

This nitpick is brought up each time someone makes an interesting observation. I can only image it is because people are trying to preempt intelligent design nonsense.

You are ofc right, it had no purpose when you talk generation to generation, the gradual tiny mutation each time did indeed serve no purpose.

But when you talk about the end product, the striped zebra, it is ok to say zebras (as the product of those millions of tiny iterations) might have evolved to discourage biting flies. Of course it could have been some other reason altogether, or a mixture of reasons but there is nothing wrong with the vocabulary, imo.

> Evolution doesn’t answer to a single why question.

Evolution selects for traits correlated with successful reproduction. Correlation doesn't imply causation. All evolution can do is say "hey, things with this trait worked better, let's build more of these."

Are flies killing (non-striped) zebras? Or would they make them infertile? Attract predators?

Flies would be messing with the zebras ability to pass on their genes in some for for this trait to be selected for.

tsetse flies are bad news, so, probably yes.

While you raise a good point about evolution being inscrutable - the stripes do effect files...

" By watching and filming the stable’s horses and zebras, the team confirmed that horseflies were much worse at alighting on the latter. The flies had no problem finding the zebras or approaching them, but couldn’t stick the landing. “You get a quarter as many landings,” Caro said. “The flies just can’t probe for a blood meal with the zebras.” "

I think the evolution angle relates to the question "Why did this trait evolve? What function does it serve?" with a potential Answer "It repels flies."

My point might have been unclear, but I didn’t doubt the usefulness of the stripes in even a slight way.

My critique was pointed at the wording. IMO it is not about why a trait evolved – there are many useless traits that envolved somewhere during special conditions and after these conditions change remain for a eternity or suddenly find a new usefulness in changed circumstances. This means pinpointing such a trait down to a single why is not a good representation of reality.

Are such observations valuable? For sure! Nature developed amazing strategies for all kind of things and not looking at these would be a waste.

I’d just be a bit more cautios with quick conclusions that involve meaning and answering why-questions, that’s all

The most interesting parts (to me):

"By watching and filming the stable’s horses and zebras, the team confirmed that horseflies were much worse at alighting on the latter. The flies had no problem finding the zebras or approaching them, but couldn’t stick the landing. “You get a quarter as many landings,” Caro said. “The flies just can’t probe for a blood meal with the zebras.”

“When we looked at the videos, we found that the flies simply aren’t decelerating when they come in to the stripes,” Caro said. Either they miss and overshoot the zebras, or they bump into the hides and bounce off. Something’s clearly throwing them off, but the details are still a mystery. Caro said that they might treat the black stripes like a pair of trees, try to fly between them, and end up colliding with the white stripes. Alternatively, the stripes might mess with their optic flow—their sense of objects moving across their visual field.

I thought it was for the same reason humans have stripes: http://mentalfloss.com/article/65092/our-skin-covered-invisi...

It's the same reason humans paint stripes on their bodies

https://www.techexplorist.com/body-painting-protects-bloodsu...

Interesting theory. Also surprising that the counter-measure to disease-carrying flies is not a stronger immune system but something that gets them fewer bites.

EDIT: but thinking about it more, nothing says multiple traits can't gain traction as a consequence of deadly pressure. I guess I never thought that much about evolution!

I wonder if CV systems will be similarly catastrophically perplexed?

Imagine laying out the zebra rug for an Amazon drone delivery

No, its pretty obvious to recognize a zebra using a neural net (e.g. resnet)

I meant with regards for reference for landings, although I imagine a drone could look around, it’s far larger than a fly.

I've wondered if you could do something similar for keeping birds from landing on flat elevated surfaces. I wasn't thinking stripes though, more like reflective holographic surfaces so the birds couldn't even identify the flat surface as flat. I'm inclined to believe that the crows would figure it out sooner or later though.

But is it as obvious to tell a distance to a zebra given it’s image?

Why didn't buffalo and bison evolve to have stripes? Seems they would benefit from having them.

I don't think that's how evolution works. Species don't gain traits that would benefit them. "Why didn't they?" seems like the wrong question :)

In the article it is mentioned that zebras have shorter hair which makes them more vulnerable to the flies. You could ask why didnt they just grow longer hair? Well probably for something else it was important to have short hair.

Local climate feels like a probable answer

Also the ability to run 60 MPH.

I think flies can detect carbon dioxide levels to find their hosts (https://journeynorth.org/tm/crane/co2_traps.html)

Why is this fact never mentioned in this article, and did they do any analysis on how wearing a coat can affect CO2 levels around a horse's body?

They did attempt using coats of solid colors with no benefit. This at least is partial testing of your hypothesis.

Fair point, that does address my hypothesis.

The study in the article tested this hypothesis and refuted it.

It in fact did not test anything about dazzle camouflage. The study [1] (linked by the linked article) did test how predators vision works and determined that Zebras camouflage doesn't serve much purpose at long ranges, but doesn't prove anything about shorter ranges where dazzle camouflage may make it easier for zebras to run away because predators aren't following them accurately.

[1]: https://journals.plos.org/plosone/article?id=10.1371/journal...

This is essentially the mechanism the article describes... I think the most plausible explanation is that it's dazzle camo, the question is what species does it dazzle?

I don't where I heard this, or if it is true, but it has been my favorite (maybe fake) animal fact:

There is a reason the stripes are BLACK and WHITE. One absorbs the light and the other reflects, which in turn makes a slight difference of air temperature right above the skin surface. The difference of temperatures in certain areas cause (slight) differences in air pressure. This can cause a shallow "wind coat" around the Zebra (and more pronounced when the animal is moving) because of the air pressure deltas all over its skin. This helps Zebra's regulate body temperatures in some very hot climates.

This theory is refuted in the very article you are commenting on.

My favorite fake animal fact now.

Did you at least do the math for that?

So if i go to the jungle i should dress like a zebra

I definitely want a zebra striped T-shirt now!

But it doesn't say if it protects from house flies :/

I'd wear a striped shirt if it could ward off the black flies in northern Wisconsin.

If the theory of evolution is correct, then there is no why to any animal trait. There's no "reason" for the traits, it only happens that maybe some traits allowed the species to survive longer and so they are still around today, but that doesn't mean "someone" enforced a certain trait with a certain purpose.

So, a more scientifically oriented title should be: What do Stripes do for Zebras? Shoo away flies.

No, that's a common mistake. In fact, there can be causation without a sentient causal entity.

Zebras have stripes because their stripes shoo away flies, which helped previous generations of zebras who had stripes thrive and pass their genes forward. Why do zebras have stripes? Because they shoo flies away and evolution ensured that that helpful trait kept passing through descendants until every zebra had it as a dominant, visible trait.

No one ever said there had to be "someone" somewhere to paint zebras black and white, that's just you using anthropomorphized evolution as a straw man/entity.

> Zebras have stripes because their stripes shoo away flies, which helped previous generations of zebras who had stripes thrive and pass their genes forward.

Not necessarily. A trait may also be there simply because it's not actively harmful, or maybe because it's a useless side-effect of another trait that is beneficial.

It may be that zebras have stripes because they are not harmful enough to prevent them from passing their genes forward. (of course, in this particular case the flies hypothesis seems more likely).

It's still a philosophical debate if such an phenomenon can be seen as cause and effect. It's a similar problem as with teleological views in eg biology and medicine: "what's the task/purpose of the lungs?" - there is no predefined task.

> which helped previous generations of zebras who had stripes thrive and pass their genes forward.

You don't know that. The article doesn't even bother to test it.

They've observed that stripes lead to fewer horsefly landings. Interesting. I guess.

But, talking about evolution is a non sequitor. Show me the data where a zebra's fecundity is related to the number of horsefly bites it receives. There isn't any.

One can speculate about such things. But, if one wishes to be scientific, test to see if there is a measurable effect.

For all we know, zebras with MORE horsefly bites are MORE likely to reproduce. There simply is no data in the article one way or the other. So bringing up evolution is just mindless unscientific just-so-storytelling.

Animal trypanosomiasis, transmitted by tsetse flies, causes "fever, weakness, and lethargy, which lead to weight loss and anemia; in some animals the disease is fatal unless treated".

Doesn't it sound like such diseases are likely to alter a zebra's fecundity?

The study involved horseflies in England... not tse-tse flies in Africa.

As far as the effect of 'such diseases' on a zebra's fecundity, I have no idea. For all we know, a feverish lethargic zebra is EASIER for a stallion to mount than a healthy zebra. Nobody knows.

The study, incidentally, did not deal with the types of flies accustomed to biting zebras. I have every reason to think a typical African biting fly would have no problem alighting on a zebra... it's what they do for a living.

While it only happens that some traits allowed the species to survive longer (or multiply more), there's still the "reason why" - there's generally a specific mechanism (or multiple mechanisms) how exactly that trait allows the species to survive longer or multiply more. As that particular mechanism is the reason for that trait being useful, it's also the reason (cause) for that trait to having outcompeted other traits.

So, there's nothing wrong with the title of "Why do Zebras have stripes [other than the obvious default non-answer 'because stripes are somehow good for them']? To Shoo Away Flies."

I.e. "why do they have Y" is "why" in the sense "what's the reason/cause of Y's continued existence".

Well, you are choosing a reason. That doesn't make it the reason.

Sure you can say Zebras have black and white stripes because their genes makes them express them in a certain way. However I could say they have stripes because it helps them shoo away flies. Someone else could say they have stripes because it makes them look pretty. Another person yet could say they only seem to have stripes because we can see those colors, but some other animals can't see them, so to us they have stripes. And then anyone could keep coming up with alternative answers. Even worse, you could ask why the mechanism that makes the Zebras have stripes works that way? And then why is that so. And then there's technically no end to it (just talk to any little kid). We just accept the first seemingly reasonable answer to a why question, and we've been trained it's rude or annoying to keep asking. But there's really no definitive answer, except whichever one you choose to accept.

The choice of reason isn't arbitrary. You could say that they have stripes because it helps them shoo away flies and someone else could say they have stripes because it makes them look pretty - but one (or both) of these answers would be wrong. The hypothesis can be falsified. We could test whether zebras do find stripes pretty in other zebras - perhaps it's not the best way to spend your time and resources, but it can be done. We can measure whether stripes discourage flies from landing, and we can measure what impact (if any) less flies has on health of zebras and their likelihood to survive until breeding. It's tricky, but it's generally possible.

There's some mechanism that makes stripes beneficial. Or perhaps there are multiple valid mechanisms - but in that case, one contributes (for example) 70% and the other 30%, and that can (with enough effort) be evaluated, and those mechanisms separated from the other alternative answers that are just guesses.

There are definitive answers. Perhaps they're hard to find out, perhaps they're hard to verify, perhaps for some aspects we'll not find out these definitive answers, but they certainly are there. You may reasonably choose that a particular answer isn't important enough to justify the resources needed to obtain that answer (and zebra stripes may well be a decent example for that), but giving in to the concept "there's really no definitive answer, except whichever one you choose to accept" is just shameful wilful ignorance. Reality is what exists no matter if you choose to accept it or not.

> Reality is what exists no matter if you choose to accept it or not

Is it? How do you know? You can't prove it. Reality to you is what you experience and you can never know what anyone else is experiencing. Reality is not objective, it depends on an observer. In fact if there are no observers, then there's no way to prove reality exists (and the concept wouldn't even make sense).

Even if there was an objective reality that was the same for all, "a reason" is a made up human concept, it is not a fundamental thing of nature/reality. You are even trying to define what a reason is in your comment.

So I would say, in this case, you calling other people willfully ignorant is just the way you deal with your reality to accept it and reject what the other person is trying to convey.

"Why do humans have teeth? To chew food"

Doesn't look bad to me, and it's the same exact point.