
Dogs' Eyes Have Changed Since Humans Befriended Them (2019) - EndXA
https://www.theatlantic.com/science/archive/2019/06/domestication-gave-dogs-two-new-eye-muscles/591868/
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EndXA
The original study can be read here:
[https://www.pnas.org/content/116/29/14677](https://www.pnas.org/content/116/29/14677)

Abstract:

> Domestication shaped wolves into dogs and transformed both their behavior
> and their anatomy. Here we show that, in only 33,000 y, domestication
> transformed the facial muscle anatomy of dogs specifically for facial
> communication with humans. Based on dissections of dog and wolf heads, we
> show that the levator anguli oculi medialis, a muscle responsible for
> raising the inner eyebrow intensely, is uniformly present in dogs but not in
> wolves. Behavioral data, collected from dogs and wolves, show that dogs
> produce the eyebrow movement significantly more often and with higher
> intensity than wolves do, with highest-intensity movements produced
> exclusively by dogs. Interestingly, this movement increases paedomorphism
> and resembles an expression that humans produce when sad, so its production
> in dogs may trigger a nurturing response in humans. We hypothesize that dogs
> with expressive eyebrows had a selection advantage and that “puppy dog eyes”
> are the result of selection based on humans’ preferences.

~~~
archi42
Was already posted in 2019 (251 points), but afaict the original study wasn't
linked back then:
[https://news.ycombinator.com/item?id=20209569](https://news.ycombinator.com/item?id=20209569)

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bitwize
Perhaps relatedly, you can often see the sclerae of dog eyes, which you can't
with wolf eyes. I think there was selection pressure there too: it was
evolutionarily advantageous for a humans to be able to signal to each other
where they were looking without speech or a gesture, and the same is probably
true of, say, canine hunting companions.

I can't really back this up, but it's something I've noticed.

~~~
gumby
That’s an interesting idea for why you can see the human sclera! (And so
clearly as well — its one of the defining features of the human face, except
in Anime). It otherwise seems like an evolutionary disadvantage.

What I like about your surmise is that, AFAIK, _canis familiaris_ is the only
animal other than the great apes that understand gestural ostention (if you
point at something a cat will look at your finger while a dog will look at the
thing you Re pointing at). As a pack-hunting animal this silent communication
is pretty important for dogs and you can see how it could have adapted to
humans.

I just did a quick search and there is a recent paper alleging that house cats
have some ability to recognize gaze but not gesture, which also suggests this
mechanism might be at work.

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alexpotato
I forget where I read this but apparently dogs have evolved to understand
human body language as well.

For example, if a dog goes into a room with a stranger and the stranger then
points to one of several buckets, the dog will generally go over to that
bucket. This is without any prior training or experience to pointing on the
dog's part.

This apparently doesn't work with children so the theory was that over time,
the dogs that responded best to human body language were more likely to
survive due to getting more treats etc.

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gadders
Our neighbour had a golden retriever who I would feed the odd treat to
(because who doesn't like dogs?). One day he saw me and came up to me and
looked at my face to see if I was looking at him, and then _with his eyebrows_
gestured to my pocket (where I normally kept treats for him) and then looked
at my face again.

Smart dog.

~~~
nemo44x
Yeah dogs get really good at a few things, especially when it comes to food.
They are really good manipulators too, generally to get food.

My dog only needs to be given a treat once by a shop owner and every walk
afterwards he’ll go up to the door of that shop.

I took him with me to pick up a framed picture once and the shop owner had a
few treats for him. We don’t often go by this shop and this was awhile ago.
And now when do walk past he pulls a bit to suggest we go inside.

Or if they find some food under a bush or something - they’ll check quite a
few times later to see if it magically restocked.

They also try things out to see if it works in getting them food. Which is why
it’s important to not fall for their tricks. Easier said than done as they
know how to use their facial expressions to get what they want.

When it comes down to it, dogs simply have a lot of time on their hands. They
get good at figuring out which sounds and actions mean what at certain times.
And they figure out how to manipulate that. Almost like inmates that have
nothing to do all day but think up schemes.

They’ll get away with whatever they can.

~~~
at_a_remove
At my Starbucks (and presumably others), dogs riding in a car in the drive-
through regularly receive "puppercinos," a cup of whipped cream. I noticed how
the dogs immediately go to the driver-side window and begin making eyes at the
baristas.

~~~
heelix
Dairy Queen does something similar. Our dog does the same thing with the pup
cups of soft serve they hand out.

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cpwright
I unfortunately know more than I would like about dog eyes, because my 4 year
old GSD had cataracts. Some of the differences the vet told me are
interesting.

Dogs vision is about 20/200 in general, and they can only use their lens to
focus 1-2 diopters (compared to about 6 for people).

Dogs can track movement and see in low light better than we can. The way that
he did an eye test was simply to drop a cotton ball, the difference before
surgery and 2 days after surgery was stark. He would ignore it before, and
afterwards his head followed it.

~~~
luckylion
> Dogs can track movement and see in low light better than we can.

This goes against my experience. When I was dog sitting my mother's dog a few
years ago and we were going for the final walk of the night, she'd regularly
get surprised by people passing us from the opposite direction. She'd notice
them 1-2 meters away and would jump back and bark, while I was easily able to
see them 5-10m away. I've had similar experiences with another dog.

Would they notice them better if they were moving side to side instead of
slowly becoming bigger while walking towards us?

~~~
archi42
Difficult to judge: Better sight doesn't mean "better human-like sight". Maybe
dogs are better at seeing fast moving gradients (e.g. when racing prey), but
have difficulties with slow changes (e.g. predator slowly closing in).

Also, maybe the dogs just assumed that /you/ would be looking out for any
"enemies", and were then just surprised because you didn't warn them about the
impeding "attack" while they had other things in mind ;-)

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AdmiralAsshat
This particular change is getting attention, but the trend is well-known:

[https://en.wikipedia.org/wiki/Neoteny#In_domestic_animals](https://en.wikipedia.org/wiki/Neoteny#In_domestic_animals)

We breed animals for bigger eyes and other features to make them cuter--to
make them look more like babies.

~~~
kipchak
I wonder if perhaps in addition to bigger eyes being cuter and therefore
preferable, we're able to form bonds with animals more easily as a result of
larger eyes- or perhaps more broadly that large eyes can be advantageous for
social bonding. Dogs and their owners engaging in mutual gazing causes similar
Oxycontin release to mother-infant gazing. I think ideas like the eyes being a
"window into the soul" are related, and we're more likely to be able to
determine if someone is trustworthy and genuine as indicators like pupil size
are involuntary.

[https://www.scientificamerican.com/article/is-the-gaze-
from-...](https://www.scientificamerican.com/article/is-the-gaze-from-those-
big-puppy-eyes-the-look-of-your-doggie-s-love/)

~~~
AdmiralAsshat
Entirely possible. I was taught the concept admittedly in a humanities course
about Middle Eastern archaeology, and it was boiled down by the professor to,
"We made our pets look cuter, more like babies. This made us feel more
paternal towards them."

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annamargot
Humans have had a very large hand in this evolution.

Dogs are probably the most heavily bred animal in the last 300-400 years. Many
(most?) breeds of dogs only exist because humans specifically bred for certain
traits.

When breeding for behavioral traits, a dog with expressive eyes who can make
humans feel a connection has gotta be a winner over ol wolf eyes over there.

~~~
teraku
While I agree with your general point, I think livestock is more heavily bred.
Chicken, cows, poultry and pigs that "live" in factory farms nowadays can't
even survive out in the wild, nor do they have particularly long life-spans.

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kingkawn
Reminds me of the Russian experiment that worked to prove that a selection
process for behavior could produce domesticated foxes. An unanticipated side
effect of the experiment after six or seven generations was that the foxes
facial phenotype began to resemble dogs:

[https://en.wikipedia.org/wiki/Domesticated_red_fox](https://en.wikipedia.org/wiki/Domesticated_red_fox)

[https://en.wikipedia.org/wiki/Dmitry_Belyayev_(zoologist)#Be...](https://en.wikipedia.org/wiki/Dmitry_Belyayev_\(zoologist\)#Belyayev's_fox_experiment)

~~~
tsdlts
This is really interesting. Does anyone know of any other instances of
behavioral traits having a direct link to an animal's appearance?

~~~
Cactus2018
Figure 2. Representatives of different families and orders show the most
specific morphological markers of domestication, white spotting on the head
(top row) and floppy ears (bottom row):

Horse, cow, pig, sheep, dog, and rabbit.

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2763232/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2763232/)

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z3t4
I don't know if this is true but I've heard that at fox farms they kill the
aggressive foxes. Resulting in the foxes getting more and more tame. So they
are basically killing dogs for their furs.

~~~
throwawayffffas
There has definitely been experimentation on the domestication of foxes, and
if I recall correctly they would sell the foxes furs when funding ran dry.
Though I don't know to what extent this applies to commercial fur farms. I
actually was not even aware that fox fur farms are a thing.

See
[https://en.wikipedia.org/wiki/Domesticated_red_fox#Experimen...](https://en.wikipedia.org/wiki/Domesticated_red_fox#Experimentation)

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wrnr
U know what is cool, human eye's sclera is white making it easier to know
where a person is looking and to trust them. As opposed to gorillas you never
know if they eying u to maul ur head.

~~~
lowdose
A small percentage of gorillas do have a human like white sclera. Linked
article includes pictures.

> Out of the 60 western lowland gorillas they considered, only 30% had
> completely dark scleras. The remaining 70% had some degree of white in their
> eyes. Of these, a small sample of 7% had all white, human-like sclera.

[http://www.bbc.com/earth/story/20150808-gorillas-with-
human-...](http://www.bbc.com/earth/story/20150808-gorillas-with-human-eyes)

~~~
wrnr
Yikes, I'd rather stair in the eyes of Darth Maul on a killing rampage

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mrlonglong
Fascinating to see what my old university has been up to!

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taneq
I started reading this expecting it to be about dogs' optics but instead it's
all about them having developed the ability to use their eyebrows for human-
style emotional expression.

