
Zebras’ stripes discourage biting flies from landing - curtis
https://www.theatlantic.com/science/archive/2019/02/why-do-zebras-have-stripes-flies/583114/
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atoav
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.

~~~
ARandomerDude
> 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.

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everdev
> unless they get very close

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

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gridspy
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.

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

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

[https://www.techexplorist.com/body-painting-protects-
bloodsu...](https://www.techexplorist.com/body-painting-protects-bloodsucking-
insects/20272/)

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deburo
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!

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zeristor
I wonder if CV systems will be similarly catastrophically perplexed?

Imagine laying out the zebra rug for an Amazon drone delivery

~~~
ipsum2
No, its pretty obvious to recognize a zebra using a neural net (e.g. resnet)

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

~~~
curtis
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.

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

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kirre245
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.

~~~
b_tterc_p
Local climate feels like a probable answer

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

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

~~~
drcode
Fair point, that does address my hypothesis.

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limbicsystem
[https://royalsocietypublishing.org/doi/10.1098/rsos.181325](https://royalsocietypublishing.org/doi/10.1098/rsos.181325)

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gpderetta
[https://en.m.wikipedia.org/wiki/Dazzle_camouflage](https://en.m.wikipedia.org/wiki/Dazzle_camouflage)

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

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thethirdone
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...](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0145679)

~~~
amvalo
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?

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danamkaplan
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.

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

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danamkaplan
My favorite fake animal fact now.

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

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skookumchuck
I definitely want a zebra striped T-shirt now!

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

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analog31
I'd wear a striped shirt if it could ward off the black flies in northern
Wisconsin.

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ta1234567890
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.

~~~
vntok
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.

~~~
lurquer
> 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.

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vntok
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?

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lurquer
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.

