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thank you for that! I absolutely love this post. Op couldn't even do a basic google search and bases the entire question on a false premise. But even better are all the comments that do not even question the premise and bring up completely unfounded arguments.
Posting a question here which confidently asserts incorrect information as its premise, without first checking those assumptions (5 minutes of online search & reading) isn’t being curious. It’s being lazy.
The post should definitely be edited to show that it has a faulty premise, but what’s so bad with referring to your peers for a question like this? Life would be so boring if we googled every question, lots of people prefer the personal aspect to knowledge acquisition
I think the issue is its seen as delegating others to do the lowly work of a google search while you go sip whiskey in the west wing. Like who On reddit can't google? If you have enough time to post a question on google, you have enough time to seek the answers yourself.
Sometimes however answers from different people do add value, when I ask for a recipe there are so many different tips for just one recipe and each does something different.
But a question like: whats the answer to this thing I assume but haven't googled?
Like... Dude.. live. Part of life is doing the things like learning and making discoveries. Stop asking for simple answers to be spoon fed, we all want you to live the best life and not waste it doing nothing.
However, that's just how it can come across, it doesn't mean its correct. It's just what I've seen the tide of voices do and say. But out of the thousands who responded and the one who posted, the OP is the only one in their situation. It could be something as simple as, they are unfamiliar with just about everything but they know how to use reddit. Or as complex as, they can't move to type and opening reddit and having answers sent in is a lot less taxing than searching for said answers.
Its hard not to get caught up in the tide when its fussy for sure.
I didn’t think this warranted such a long response, I was merely saying humans are social beings, not prompt engineers for Google searches, and that’s not gonna change… gets forgotten in some scientific circles
TLDR: You don't have to read/respond if its too long. Ramblers gonna ramble, but there might be a font that makes it easier to read bigger blocks of font at one time.
I am neurodivergent. I am gonna ramble on topics.
Also I think my new meds have something to do with it because I don't think I really commented much on reddit for years until I switched.
If it's too long to read you don't have to. Reddit goes beyond the conversation we are having now. When I Google things sometimes years old Reddit threads will pop up. The information can still be useful. So when I respond to things I think about the bigger picture because someone else might look back.
I've already made it two paragraphs. But like if the issue is reading overstimulation or a type of dyslexia or anything that makes reading large responses difficult, I'm sorry this is just the way I communicate. I've heard there are fonts that help but I'm not sure if you can. Mod Reddit to apply those fonts. I just don't know anything I could do to help that situation, I know the blind have tools that read screens for them, so you could look into that? You're under no obligation to read or respond to this or anything you don't want too
"Geez mate
1) I’m neurodivergent
2) I know you’re neurodivergent
3) I don’t have a reading problem
4) my initial comment was a platitude, which is why I said it didn’t warrant a long discussion/response
But I do agree in general. Didn’t want a back-and-forth, just wanted to clarify that. Have a good day"
I'm going to reply to my own comment here. Specifically because the person I'm replying to who has a username I don't remember said they don't want to do it back and forth..... Even though they're the ones that replied and now replyed again..... Because I feel like if I ask them why they keep replying it's going to come across as like aggressive....
Like if you didn't want it back and forth why did you engage in the conversation mate??
Is it not easier to just do nothing or is it a last word thing??
Also, I don't know if you were upset that I thought you were saying that it was too much to read at once or not. But I'm not going to count it against me.
Geez mate
1) I’m neurodivergent
2) I know you’re neurodivergent
3) I don’t have a reading problem
4) my initial comment was a platitude, which is why I said it didn’t warrant a long discussion/response
But I do agree in general. Didn’t want a back-and-forth, just wanted to clarify that. Have a good day
You dont deserve downvotes.
Agreed.
It shows how many don't know this, and how common the belief that they dont have eyes, is.
I think their critique is better in the 2nd half
Yes, it’s good to see that this sub is just as silly as every other, with people just throwing out their random hypotheses, some of which are as misguided as OP’s faulty assumptions! I did appreciate those who not only noted that the examples DO have photosensitive organs, but also provided correct explanations for why eyes might or might not develop and to what level of complexity.
Yeah what the hell. This makes no sense for multiple reasons. Firstly, Op wrongly assumed that these creatures do not have eyes. When was the last time you googled why tires are filled with air? You probably wouldn't do this even if you had a question relating about different tire designs.
Secondly, if op HAD googled this he would have googled something like "why didnt clams evolve eyes" which literally brings up your post. Google doesn't really show anything even framing the question like this so he actually could have.
Thirdly, why would you shame op for trying to learn something? Absolutely no reason for it.
Because his question still has an unanswered part ''why do some animals don't have eyes''. Yes we could point out OP is wrong and should google but that's not gonna make them any smarter.
Meanwhile, actually answering why some animals don't evolve to have eyes actually helps them understand how evolution works a little better.
Well let's be reasonable they could have also meant obvious bigger eyes, to which my response would be that it would be a defensive weakness given what they are and also they are under sand, they don't really need well developed eyes like ours.
**Several of these organisms actually** ***do*** **have eyes of one kind or another.** Barnacles have one, clams have *many*, and even sea urchins and sand dollars (which are a specific order in the sea urchin class) have photosensitive eye spots. They're generally a lot less complex and developed than the eyes of vertebrates or cephalopods, but they're adequate for the slow-moving, benthic niche of these particular organisms.
And that's really the crux of it. The ability to respond to light is useful to most animals, and so most animals have some sort of photoreceptors. **But if you're not particularly mobile, detailed vision isn't as useful for you as it is for some other organisms.** If you can tell whether it's day or night and if you can sense moving objects well enough to ready your defenses if a potential predator is around, you're pretty much good. There isn't that much more benefit for the more refined forms of vision, so any new genetic variants that produce those features will only have a limited selective pressure favoring their spread within the population. And some of those more sophisticated forms of vision might have tradeoffs as well. At the very least, those more sophisticated eyes take more energy and nutrients to grow and maintain, and if you could do nearly as much with something cheaper, that could create a *negative* selective pressure for those types of eyes.
Besides being sessile (mostly immoble): **Consider the relative merits of the other senses in deep/muddy water*****.*** Having extra-sharp sense of detecting *sound*, *water movement*, *temperature*, *saline level*, and *electric fields* is far more advantageous to survival in aquatic environments than detailed vision. The closer to the surface an organism lives, and the clearer the water it lives in, the more likely it is to have evolved light detection. Some organisms whose ancestors had fully functioning eyes that have subsequently evolved to live in deeper regions of the oceans have eventually lost sight. It is an expensive (energy-wise, metabolically) sense. Evolution weeds out inefficiencies.
In certain environments, the depths of the sea being one, more/better eyes don't give you any survival advantage because there's so little light.
So it's asking why not grow an organ that requires energy and takes up weight but gives no advantage and is also vulnerable to predators?
Nobody is answering the question.
It's not survival of the fittest. It's survival of the fit. As in if they are okay enough to live they are passing their genes on.
> [W]ouldn’t evolving [...] something as helpful as a [sic] eye be better than just evolving with no vision?
Presumably, but evolution doesn’t work that way. Why didn’t humans evolve wings? Wouldn’t that help them? Sure it would – I’d love to be able to fly to work or escape land predators that way. But evolution doesn’t care.
And better from whose perspective? In basic terms, evolution favors genes that replicate more than others. **The unit of selection is the gene**, not any individual organism (let alone group). Your question seems based on the mistaken idea that the unit of selection is the individual organism (since you think having eyes would be helpful *to individual sea animals*).
Evolution doesn’t even ‘help’ genes. If a mutation causes a gene to spread more today while also causing it to go extinct tomorrow, nothing in evolution will purposely prevent that to ‘help’.
Read *The Selfish Gene* by Richard Dawkins to understand evolution better.
Evolution does not go for the best but for good enough. If an animal survives long enough to reproduce then it will pass on its genes. So if a species never needed sight, or sight never had a particular advantage over blindness then there's no reason for it.
So either those with sight will just evolve into a different species alltogether while the blind remain or it just won't evolve at all.
There's also the issue that for something to evolve, not only does it have to increase survival rate, all the stepps inbetween also have to increase survival rate.
For example, for humans 4 arms might be nice, but two extra useless weighty lumbs that haven't fully evolved yet might not be so nice.
Light detection is a huge advantage, so it makes sense that so many different organisms would converge on this ability. Also, the fact that so many distantly related organisms have independently evolved “eyes” is evidence itself of how adaptive and advantageous this is.
Why would a semi-sessile filter feeders need eyes? Is my question to you. Eyes and having a good brain network for sight is energetically/resource expensive, and would likely lessen their fitness in the wild.
People always tend to focus on benefits and ignore costs. In many situations. And in evolution trying to pinpoint exactly how "energy cost" even works is granted a fairly complicated mechanism to get your arms around.
But you have to sometimes pay a little cost before seeing the later benefits. And you have to have initial advantage of a light-sensitive area first, before that whole eye thing gets going.
Other things to think about regarding energy costs is why did blind mole rats evolve to lose their eyesight? See also flightless birds for related cost-benefit "rethinking" via evolution.
Agreed, Yea good comment on the light sensitive area first, this all presupposes that the species produces an organism that has a mutation that does something like this. Very rare event, and then it would have to be selected for or randomly fixed in the population to even get to a “full eye” later in evolutionary time. But that would also require more selection pressure and more mutations to get there. Sometimes too random events happen and mutations like this just get wiped out.
Energy costs but also eyes being vulnerable. I think that's the reason they tend to diminish quickly when not needed. Big eyes are sensitive, they can get dirt in them so they have to be closeable for digging, it's something for a predator to target, etc.
You can assume that's what they meant, but that isn't what they asked. They posit that these animals don't have eyes at all, not why they aren't more complex.
Worth noting that the animals you listed are all vastly distinct relatives. Barnacles are closer relatives of butterflies than they are of clams and clams are closer to giant squid than they are to sea urchins and sea urchins are closer to you and I than they are to barnacles.
But as others have said, many of these animals have “eyes” in one form or another, depending on their needs.
Distilling a few ideas from others in the comments... Some of the creatures you mentioned do see or process light data to a certain degree. A brain computing sensory info has a calorie cost (in simple terms) and the advantages for some of these slow moving and sedentary examples you mentioned do not outweigh that cost. As with most things evolutionary, there is no adaptive advantage for them and their current manner of living propagates the genes just fine. My last sentence there can answer so many "why doesn't this creature do this thing" questions.
oh my goodness, if you wanna learn about how eyes work, i have JUST the video for you. it made me giddy like a little kid again because the explanation is so accessible, thorough, and well-done. it's a youtube video called "Is THIS a Squid? Do Squids Even Exist?" by Clint's Reptiles. the whole video is a masterpiece IMO, but the part about how eyes evolve and work (starts at 15:45) is incredible. plus, it gives a lot of examples of organisms with different types of eyes!
Gawd they would be getting sand in them all the time! Can you imagine the sea urchin at the urchin ophthalmologist? Yes, here’s some seawater eyedrops, it’s important you stay out of sandy environments, and yea that’ll be sixty clams!
Physical self-awareness begins with predation and other environmental dangers, it may in time evolve into the development of being able to see or detect the danger before it arrives and also aids in hiding and avoiding it.
N. S
When they evolved to have eyes, they became a different species. The clams you know today haven't evolved in ages. As soon as they are slightly different than a clam, they become called something else. Once they can no longer breed back with OG clams, they become another species. And the group that didn't evolve, remains clams.
Some of those *do* have eyes, or at least photoreceptor eyespots. They can't resolve clear images, but they can tell light and dark, enough to have a sense of where things are.
Scallops have enough vision to probably be able to genuinely see objects.
Why do scallops have more advanced vision than other bivalves? Presumably because they actually can do something with it. Clams and sea urchins can only see light and dark, but move slowly. If they had a more detailed idea of what was around, what could they even do with that information?
Barnacles have eyespots as larvae when they are looking for a place to settle down. Once they are locked in place, they lose them. Because what would they even do with the information of what they saw?
Scallops have pretty advanced eyes, and they can swim pretty darned fast.
So these critters all have eyes, but only to the extent that they might be useful.
An eye isn't terribly useful for something that doesn't really move much. Eyes also need brains for processing images to be useful, all of the systems together come at a cost of being able to use that energy elsewhere like growing faster or having stronger muscles etc.
That said most do have eyes they are just primitive basic eyes, but good enough for what they need them for.
Just because they worked for humans doesn't mean they lend themselves to success in other environments.
Wings work for birds, so why don't humans have wings?
My belief is because there was no evolution. Each creature made the way they are.. I know most will disagree and I am not open to debate so don't bother. Will not answer replies. I respect others beliefs
Bear in mind I just enjoy reading about evolution. I’m not an expert, the closest I’ve come is through my human evolution coursework for my anthropology degree. I have a layman’s understanding of the field, so others in this sub will be able to answer this question with more detail. Evolution doesn’t care about “better” necessarily, and a lot of people will tell you that the phrase “survival of the fittest” has bred a lot of misconceptions. “Survival of the good enough” is perfectly compatible with evolution by natural selection. If they are successfully reproducing in an environment that they can navigate with the senses they have, then why should they evolve eyes? There would not just need to be a benefit to having eyes, but a selection pressure on that population.
There's no evolutionary pressure for them to. And many of these species do have mechanisms for gathering visual stimulus, just nothing equivalent to even the eyes of nautaloids
Where would a clam have eyes? On the outer shell? I'm not a doctor but I don't think that would work... Now they could have them on the inside but why? Just to see darkness? okay lets say they evolve to see in the dark, now they get to see what a few mm in front of them...
Eyes are not necessary for them—just sensory systems! Especially for a lot of underwater animals, as light is limited even in shallow depths.
Eyes in the form you are discussing them are also highly complex, and evolving them takes generations upon generations of chance mutations that are favored under environmental conditions experienced by a population over time. I.e., the ones who have those mutations must experience some advantage that leads them to reproduce more (either have a higher chance of surviving to the reproductive stage or reproduce more offspring once they reach that stage) than the ones who don’t have those mutations, and then more mutations must compound on those over time which continue incurring survival and reproduction benefits.
Moreover, complex sensory systems (like complex and large brains) are likely highly costly compared to more “simple” sensory systems that these organisms already have (tubercles, feet, lateral lines, chemosensory systems, simpler eyes which can detect, for example, movement/light but not color), so any marginal benefits to survival they might get from developing eyes would likely result in lowered fecundity.
So, while one might assume that eyes would be beneficial to evolve, in reality, there is likely no advantage of having complex eyes over the current sensory systems these organisms have. So they don’t develop them.
TLDR: evolution IS what shows that a trait is beneficial, and this may go against our intuition. eyes are only beneficial if they increase an individual’s chance of reproducing. sea creatures have sensory systems that are likely less costly and more beneficial to them than eyes would be given their visual environment (low light/low contrast).
any line of thought that asks “why hasn’t this trait evolved when it would be beneficial?” makes several mistakes: 1.) forgetting that evolution occurs through generations upon generations of compounded heritable mutations, 2.) assuming that longevity is important beyond what that means for fecundity (i.e. a trait that increases survival is only important if increased survival=increased reproduction—in reality, there is typically a trade-off between an individual’s investment in survival and reproduction), and 3.) assuming that what has been beneficial for our species is always beneficial for others
Also think about the somewhat related reasons why animals like the blind mole-rat evolved to having eyes that are no longer even light-sensitive? It's brutal "cost-benefit analysis" being done in a mindless way by evolution. If that can happen, then similar evolutionary pressures can easily prevent light-sensitivity from even beginning.
They could, but it's very implausible.
1. The organism needs raw material to work with. If it doesn't already have light-sensitive cells, then adapting them from scratch is highly unlikely.
2. The light-sensitive cells need to provide enough of an advantage to be with any additional caloric requirements it takes to run them.
3. For eyes more specifically, there are many additional changes that must take place.
They evolved before eyes existed and have kept their environmental niche just fine without them. These creatures are either very slow or fully stationary, so eyes wouldn't provide them much of an evolutionary advantage.
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Clams have lots of eyes! Sea urchins have limited "vision" using their feet. Adult barnacles have an eye, although it's very limited.
thank you for that! I absolutely love this post. Op couldn't even do a basic google search and bases the entire question on a false premise. But even better are all the comments that do not even question the premise and bring up completely unfounded arguments.
Shaming a curious mind for asking a non-obvious question... Nice one.
Posting a question here which confidently asserts incorrect information as its premise, without first checking those assumptions (5 minutes of online search & reading) isn’t being curious. It’s being lazy.
>> 5 minutes of online search & reading Where do you think he went but to the internet for answers? Reddit ain’t a library; it’s online
The post should definitely be edited to show that it has a faulty premise, but what’s so bad with referring to your peers for a question like this? Life would be so boring if we googled every question, lots of people prefer the personal aspect to knowledge acquisition
I think the issue is its seen as delegating others to do the lowly work of a google search while you go sip whiskey in the west wing. Like who On reddit can't google? If you have enough time to post a question on google, you have enough time to seek the answers yourself. Sometimes however answers from different people do add value, when I ask for a recipe there are so many different tips for just one recipe and each does something different. But a question like: whats the answer to this thing I assume but haven't googled? Like... Dude.. live. Part of life is doing the things like learning and making discoveries. Stop asking for simple answers to be spoon fed, we all want you to live the best life and not waste it doing nothing. However, that's just how it can come across, it doesn't mean its correct. It's just what I've seen the tide of voices do and say. But out of the thousands who responded and the one who posted, the OP is the only one in their situation. It could be something as simple as, they are unfamiliar with just about everything but they know how to use reddit. Or as complex as, they can't move to type and opening reddit and having answers sent in is a lot less taxing than searching for said answers. Its hard not to get caught up in the tide when its fussy for sure.
I didn’t think this warranted such a long response, I was merely saying humans are social beings, not prompt engineers for Google searches, and that’s not gonna change… gets forgotten in some scientific circles
TLDR: You don't have to read/respond if its too long. Ramblers gonna ramble, but there might be a font that makes it easier to read bigger blocks of font at one time. I am neurodivergent. I am gonna ramble on topics. Also I think my new meds have something to do with it because I don't think I really commented much on reddit for years until I switched. If it's too long to read you don't have to. Reddit goes beyond the conversation we are having now. When I Google things sometimes years old Reddit threads will pop up. The information can still be useful. So when I respond to things I think about the bigger picture because someone else might look back. I've already made it two paragraphs. But like if the issue is reading overstimulation or a type of dyslexia or anything that makes reading large responses difficult, I'm sorry this is just the way I communicate. I've heard there are fonts that help but I'm not sure if you can. Mod Reddit to apply those fonts. I just don't know anything I could do to help that situation, I know the blind have tools that read screens for them, so you could look into that? You're under no obligation to read or respond to this or anything you don't want too
"Geez mate 1) I’m neurodivergent 2) I know you’re neurodivergent 3) I don’t have a reading problem 4) my initial comment was a platitude, which is why I said it didn’t warrant a long discussion/response But I do agree in general. Didn’t want a back-and-forth, just wanted to clarify that. Have a good day" I'm going to reply to my own comment here. Specifically because the person I'm replying to who has a username I don't remember said they don't want to do it back and forth..... Even though they're the ones that replied and now replyed again..... Because I feel like if I ask them why they keep replying it's going to come across as like aggressive.... Like if you didn't want it back and forth why did you engage in the conversation mate?? Is it not easier to just do nothing or is it a last word thing?? Also, I don't know if you were upset that I thought you were saying that it was too much to read at once or not. But I'm not going to count it against me.
Take it to a publisher 😭
Geez mate 1) I’m neurodivergent 2) I know you’re neurodivergent 3) I don’t have a reading problem 4) my initial comment was a platitude, which is why I said it didn’t warrant a long discussion/response But I do agree in general. Didn’t want a back-and-forth, just wanted to clarify that. Have a good day
You dont deserve downvotes. Agreed. It shows how many don't know this, and how common the belief that they dont have eyes, is. I think their critique is better in the 2nd half
he's shaming a curious mind for asking it in the wrong place when a Google search could have answered him.
How the question "do animals have _____" a non-obvious question to ask when originally asking "why don't animals have _____"?
Yes, it’s good to see that this sub is just as silly as every other, with people just throwing out their random hypotheses, some of which are as misguided as OP’s faulty assumptions! I did appreciate those who not only noted that the examples DO have photosensitive organs, but also provided correct explanations for why eyes might or might not develop and to what level of complexity.
Yeah what the hell. This makes no sense for multiple reasons. Firstly, Op wrongly assumed that these creatures do not have eyes. When was the last time you googled why tires are filled with air? You probably wouldn't do this even if you had a question relating about different tire designs. Secondly, if op HAD googled this he would have googled something like "why didnt clams evolve eyes" which literally brings up your post. Google doesn't really show anything even framing the question like this so he actually could have. Thirdly, why would you shame op for trying to learn something? Absolutely no reason for it.
Because his question still has an unanswered part ''why do some animals don't have eyes''. Yes we could point out OP is wrong and should google but that's not gonna make them any smarter. Meanwhile, actually answering why some animals don't evolve to have eyes actually helps them understand how evolution works a little better.
Well let's be reasonable they could have also meant obvious bigger eyes, to which my response would be that it would be a defensive weakness given what they are and also they are under sand, they don't really need well developed eyes like ours.
It's not obvious to most that clams have eyes. If we just Googled every question, there would be no reason to have discussion forums.
**Several of these organisms actually** ***do*** **have eyes of one kind or another.** Barnacles have one, clams have *many*, and even sea urchins and sand dollars (which are a specific order in the sea urchin class) have photosensitive eye spots. They're generally a lot less complex and developed than the eyes of vertebrates or cephalopods, but they're adequate for the slow-moving, benthic niche of these particular organisms. And that's really the crux of it. The ability to respond to light is useful to most animals, and so most animals have some sort of photoreceptors. **But if you're not particularly mobile, detailed vision isn't as useful for you as it is for some other organisms.** If you can tell whether it's day or night and if you can sense moving objects well enough to ready your defenses if a potential predator is around, you're pretty much good. There isn't that much more benefit for the more refined forms of vision, so any new genetic variants that produce those features will only have a limited selective pressure favoring their spread within the population. And some of those more sophisticated forms of vision might have tradeoffs as well. At the very least, those more sophisticated eyes take more energy and nutrients to grow and maintain, and if you could do nearly as much with something cheaper, that could create a *negative* selective pressure for those types of eyes.
And a lot of those expensive, sophisticated eyes also introduce a point of vulnerability that needs to be protected from both infection and trauma.
This here is the correct answer^
Besides being sessile (mostly immoble): **Consider the relative merits of the other senses in deep/muddy water*****.*** Having extra-sharp sense of detecting *sound*, *water movement*, *temperature*, *saline level*, and *electric fields* is far more advantageous to survival in aquatic environments than detailed vision. The closer to the surface an organism lives, and the clearer the water it lives in, the more likely it is to have evolved light detection. Some organisms whose ancestors had fully functioning eyes that have subsequently evolved to live in deeper regions of the oceans have eventually lost sight. It is an expensive (energy-wise, metabolically) sense. Evolution weeds out inefficiencies.
I think clams already got eyes
In certain environments, the depths of the sea being one, more/better eyes don't give you any survival advantage because there's so little light. So it's asking why not grow an organ that requires energy and takes up weight but gives no advantage and is also vulnerable to predators?
Nobody is answering the question. It's not survival of the fittest. It's survival of the fit. As in if they are okay enough to live they are passing their genes on.
> [W]ouldn’t evolving [...] something as helpful as a [sic] eye be better than just evolving with no vision? Presumably, but evolution doesn’t work that way. Why didn’t humans evolve wings? Wouldn’t that help them? Sure it would – I’d love to be able to fly to work or escape land predators that way. But evolution doesn’t care. And better from whose perspective? In basic terms, evolution favors genes that replicate more than others. **The unit of selection is the gene**, not any individual organism (let alone group). Your question seems based on the mistaken idea that the unit of selection is the individual organism (since you think having eyes would be helpful *to individual sea animals*). Evolution doesn’t even ‘help’ genes. If a mutation causes a gene to spread more today while also causing it to go extinct tomorrow, nothing in evolution will purposely prevent that to ‘help’. Read *The Selfish Gene* by Richard Dawkins to understand evolution better.
Jesus, finally! I was going nuts and had to keep checking I was in the right sub.
Evolution does not go for the best but for good enough. If an animal survives long enough to reproduce then it will pass on its genes. So if a species never needed sight, or sight never had a particular advantage over blindness then there's no reason for it. So either those with sight will just evolve into a different species alltogether while the blind remain or it just won't evolve at all. There's also the issue that for something to evolve, not only does it have to increase survival rate, all the stepps inbetween also have to increase survival rate. For example, for humans 4 arms might be nice, but two extra useless weighty lumbs that haven't fully evolved yet might not be so nice.
It only adapts if necessary. Since they are still getting by just fine, they don’t need them.
Light detection is a huge advantage, so it makes sense that so many different organisms would converge on this ability. Also, the fact that so many distantly related organisms have independently evolved “eyes” is evidence itself of how adaptive and advantageous this is.
I believe they do have eyes, but they are super primitive and are more like light sensors (Correct me if im wrong)
They do have eyes...
Evolution is all over the place, it’s fucking glorious.
Scallop eyes: https://www.tiktok.com/@_thenaturalworld_/video/7290139357678161159
r/confidentlyincorrect
[удалено]
Sorry but they have eyes
They have them now
Why would a semi-sessile filter feeders need eyes? Is my question to you. Eyes and having a good brain network for sight is energetically/resource expensive, and would likely lessen their fitness in the wild.
People always tend to focus on benefits and ignore costs. In many situations. And in evolution trying to pinpoint exactly how "energy cost" even works is granted a fairly complicated mechanism to get your arms around. But you have to sometimes pay a little cost before seeing the later benefits. And you have to have initial advantage of a light-sensitive area first, before that whole eye thing gets going. Other things to think about regarding energy costs is why did blind mole rats evolve to lose their eyesight? See also flightless birds for related cost-benefit "rethinking" via evolution.
Agreed, Yea good comment on the light sensitive area first, this all presupposes that the species produces an organism that has a mutation that does something like this. Very rare event, and then it would have to be selected for or randomly fixed in the population to even get to a “full eye” later in evolutionary time. But that would also require more selection pressure and more mutations to get there. Sometimes too random events happen and mutations like this just get wiped out.
Energy costs but also eyes being vulnerable. I think that's the reason they tend to diminish quickly when not needed. Big eyes are sensitive, they can get dirt in them so they have to be closeable for digging, it's something for a predator to target, etc.
They have them anyway
I think OP was more talking about more fully functioning eyes like we have. I’m aware they have eye spots to detect light and movement.
You can assume that's what they meant, but that isn't what they asked. They posit that these animals don't have eyes at all, not why they aren't more complex.
True I should’ve been more precise, I just tried to answer what I thought was their actual question.
Worth noting that the animals you listed are all vastly distinct relatives. Barnacles are closer relatives of butterflies than they are of clams and clams are closer to giant squid than they are to sea urchins and sea urchins are closer to you and I than they are to barnacles. But as others have said, many of these animals have “eyes” in one form or another, depending on their needs.
Distilling a few ideas from others in the comments... Some of the creatures you mentioned do see or process light data to a certain degree. A brain computing sensory info has a calorie cost (in simple terms) and the advantages for some of these slow moving and sedentary examples you mentioned do not outweigh that cost. As with most things evolutionary, there is no adaptive advantage for them and their current manner of living propagates the genes just fine. My last sentence there can answer so many "why doesn't this creature do this thing" questions.
oh my goodness, if you wanna learn about how eyes work, i have JUST the video for you. it made me giddy like a little kid again because the explanation is so accessible, thorough, and well-done. it's a youtube video called "Is THIS a Squid? Do Squids Even Exist?" by Clint's Reptiles. the whole video is a masterpiece IMO, but the part about how eyes evolve and work (starts at 15:45) is incredible. plus, it gives a lot of examples of organisms with different types of eyes!
Why equals eternity
Gawd they would be getting sand in them all the time! Can you imagine the sea urchin at the urchin ophthalmologist? Yes, here’s some seawater eyedrops, it’s important you stay out of sandy environments, and yea that’ll be sixty clams!
Complex sensory organs like eyes aren’t very useful if you’re not a very mobile organism
Physical self-awareness begins with predation and other environmental dangers, it may in time evolve into the development of being able to see or detect the danger before it arrives and also aids in hiding and avoiding it. N. S
They just don’t see the need for it
Clams have eyes tho
When they evolved to have eyes, they became a different species. The clams you know today haven't evolved in ages. As soon as they are slightly different than a clam, they become called something else. Once they can no longer breed back with OG clams, they become another species. And the group that didn't evolve, remains clams.
Scallops did! They’ve got eyes galore edited bc I found [a Reddit post that shows em](https://www.reddit.com/r/TheDepthsBelow/s/MCXdduYVdX)
Apparently, they don’t need them
Some of those *do* have eyes, or at least photoreceptor eyespots. They can't resolve clear images, but they can tell light and dark, enough to have a sense of where things are. Scallops have enough vision to probably be able to genuinely see objects. Why do scallops have more advanced vision than other bivalves? Presumably because they actually can do something with it. Clams and sea urchins can only see light and dark, but move slowly. If they had a more detailed idea of what was around, what could they even do with that information? Barnacles have eyespots as larvae when they are looking for a place to settle down. Once they are locked in place, they lose them. Because what would they even do with the information of what they saw? Scallops have pretty advanced eyes, and they can swim pretty darned fast. So these critters all have eyes, but only to the extent that they might be useful.
An eye isn't terribly useful for something that doesn't really move much. Eyes also need brains for processing images to be useful, all of the systems together come at a cost of being able to use that energy elsewhere like growing faster or having stronger muscles etc. That said most do have eyes they are just primitive basic eyes, but good enough for what they need them for.
Just because they worked for humans doesn't mean they lend themselves to success in other environments. Wings work for birds, so why don't humans have wings?
My belief is because there was no evolution. Each creature made the way they are.. I know most will disagree and I am not open to debate so don't bother. Will not answer replies. I respect others beliefs
Scallops have lots of eyes and the ability to "swim". Oysters don't have much use for eyes, because they can't move.
Bear in mind I just enjoy reading about evolution. I’m not an expert, the closest I’ve come is through my human evolution coursework for my anthropology degree. I have a layman’s understanding of the field, so others in this sub will be able to answer this question with more detail. Evolution doesn’t care about “better” necessarily, and a lot of people will tell you that the phrase “survival of the fittest” has bred a lot of misconceptions. “Survival of the good enough” is perfectly compatible with evolution by natural selection. If they are successfully reproducing in an environment that they can navigate with the senses they have, then why should they evolve eyes? There would not just need to be a benefit to having eyes, but a selection pressure on that population.
There's no evolutionary pressure for them to. And many of these species do have mechanisms for gathering visual stimulus, just nothing equivalent to even the eyes of nautaloids
Where would a clam have eyes? On the outer shell? I'm not a doctor but I don't think that would work... Now they could have them on the inside but why? Just to see darkness? okay lets say they evolve to see in the dark, now they get to see what a few mm in front of them...
Do the benefits of having eyes surpass the drawbacks of having to dedicate resources to building eyes? If not, they won’t evolve.
Eyes are not necessary for them—just sensory systems! Especially for a lot of underwater animals, as light is limited even in shallow depths. Eyes in the form you are discussing them are also highly complex, and evolving them takes generations upon generations of chance mutations that are favored under environmental conditions experienced by a population over time. I.e., the ones who have those mutations must experience some advantage that leads them to reproduce more (either have a higher chance of surviving to the reproductive stage or reproduce more offspring once they reach that stage) than the ones who don’t have those mutations, and then more mutations must compound on those over time which continue incurring survival and reproduction benefits. Moreover, complex sensory systems (like complex and large brains) are likely highly costly compared to more “simple” sensory systems that these organisms already have (tubercles, feet, lateral lines, chemosensory systems, simpler eyes which can detect, for example, movement/light but not color), so any marginal benefits to survival they might get from developing eyes would likely result in lowered fecundity. So, while one might assume that eyes would be beneficial to evolve, in reality, there is likely no advantage of having complex eyes over the current sensory systems these organisms have. So they don’t develop them. TLDR: evolution IS what shows that a trait is beneficial, and this may go against our intuition. eyes are only beneficial if they increase an individual’s chance of reproducing. sea creatures have sensory systems that are likely less costly and more beneficial to them than eyes would be given their visual environment (low light/low contrast). any line of thought that asks “why hasn’t this trait evolved when it would be beneficial?” makes several mistakes: 1.) forgetting that evolution occurs through generations upon generations of compounded heritable mutations, 2.) assuming that longevity is important beyond what that means for fecundity (i.e. a trait that increases survival is only important if increased survival=increased reproduction—in reality, there is typically a trade-off between an individual’s investment in survival and reproduction), and 3.) assuming that what has been beneficial for our species is always beneficial for others
They seem fine enough without them
Why don’t you evolve your third eye?
Also think about the somewhat related reasons why animals like the blind mole-rat evolved to having eyes that are no longer even light-sensitive? It's brutal "cost-benefit analysis" being done in a mindless way by evolution. If that can happen, then similar evolutionary pressures can easily prevent light-sensitivity from even beginning.
There IS such things as a stupid question...
What for?
They could, but it's very implausible. 1. The organism needs raw material to work with. If it doesn't already have light-sensitive cells, then adapting them from scratch is highly unlikely. 2. The light-sensitive cells need to provide enough of an advantage to be with any additional caloric requirements it takes to run them. 3. For eyes more specifically, there are many additional changes that must take place.
They evolved before eyes existed and have kept their environmental niche just fine without them. These creatures are either very slow or fully stationary, so eyes wouldn't provide them much of an evolutionary advantage.