Revisiting a topic previously discussed here.
Interested in comments you all might have on the OP and any followup comments at Peaceful Science.
106 thoughts on “A complex adaptation: the eye”
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The Skeptical Zone
"I beseech you, in the bowels of Christ, think it possible that you may be mistaken."
There’s nothing much in that OP. And thus far the followup comments are by you, and just more of the same.
I get that you didn’t like the book. If your OP had been a book review, maybe I would be able to work out what you didn’t like about the book.
But it seems that you are trying to start an argument with the author of the book. And unless that author steps in to respond, I’m not expecting there to be anything to discuss.
Mung, thank you first of all for breaking the trend of absolutely nonsensical OPs that have been going lately. Even where we disagree here, at least you have written something coherent that seems to me worthy to discuss.
I think the most critical parts are these where you quote the book and then write in that post:
I agree that these are separate questions. But I do think they are related, and they actually do tie together with Roger’s later comment about common descent.
You quote him again, and write:
I think the common descent angle is important in for the purpose of substantiating the fact that eyes are evolving entities. That eyes have in fact evolved over geological time, and for that purpose common descent can be brought in to test the prediction Rogers makes:
If eyes did evolve, then closely related species should have similar eyes.
If their eyes are not identical, but different, then that shows that their eyes have changed since their common ancestor. Even if only by a small amount, this implies eyes do in fact change.
You don’t quote Rogers making a case for the reality or efficacy of natural selection’s ability to fix different alleles in a population, so at least in the part you quote I agree his case for natural selection being the mechanism responsible for fixing different alleles in the population is missing.
But here I think it is important to remind ourselves of two things you wrote: First of all from your op:
But you later scold Rogers for not answering this question:
So here you’re asking whether we can know that evolution took some particular path, and that natural selection is what made that happen. Can we attribute a particular change to natural selection? Well sure if there is a demonstrable difference in adaptive value between them.
But I think there’s a difference between whether natural selection COULD do it, and whether it DID do it. And the case for either can rest on inferences from different lines of evidence.
Second, it is important to remind ourselves that you have agreed that natural selection takes place. There is differential reproductive success. You write in the other thread here that
I take that to mean you accept that carriers of two different alleles can be in competition with each other, and that selection can fix an allele over antother, if that allele has a stronger positive effect on reproductive success.
Given that, it seems to me that combined with Roger’s two observations from comparative biology, that should essentially settle the matter with respect to the question you first pose: “How could all this have evolved by natural selection?”
It is ultimately an inference of course, not a deductive proof. We can’t prove that the different steps in the evolution of eyes was fixed by natural selection. But is that even necessary for your first question? We can’t prove beyond doubt that natural selection did it, but we do have good reasons thinking that it could because we know natural selection operates in the present, and different eye morphologies have different advantages depending on the environment and lifestyle of the organism.
I think the case would derive from these facts:
1. Natural selection can and does take place, and does fix different alleles because they have different effects on reproductive success.
2. There are different eye morphologies in the animal kingdom some of which are plausible as putative functional intermediates between others.
3. The implied intermediates can therefore support life and a functional sense of sight.
3. They each have their advantages and disadvantages depending on different environments.
4. Minor differences between closely related species that share common descent do exist, which shows that eyes do in fact evolve (here meaning change) over geological time scales (so the different eyes haven’t remained static).
The most plausible inference from these facts is then that the eye could have evolved by natural selection. The set of observations to be explained (different eye morphologies, their different adaptive advantages, and their distribution in different species), is best and well explained by the action of natural selection on different eye morphology mutants under different environmental circumstances. It is the model that well and best accounts for the data.
With respect to your later question (can we show that natural selection is what did it?), we’d need to have some sort of evidence that natural selection really was what cause particular alleles associated with specific eye morphologies to rise to fixation. Which I don’t think can be done for genes that old (the genes that establish the basic morphology of the vertebrate eye go back before the cambrain afaik). It CAN be done for much younger genes, such as the ones associated with different types of color vision in ourselves and our primate cousins. There are population genetic methods that can be employed to look for evidence of positive selection on particular genetic loci using comparative genetics.
It has nothing to do with whether or not I liked the book. I am addressing a specific argument from the book. Please focus on the argument.
The followup comments assume that the reader understands the context. If you don’t understand them I would be happy to explain.
I like how I can’t count to 5. xD
First, let me echo Rumraket’s thanks for a coherent and interesting post.
The post can also serve as an informal A/B comparison of the quality and number of comments at TSZ versus PS.
I want to focus on an issue that Rumraket also referred to: Namely, the nature of scientific reasoning and explanation. At PS, your post includes:
To me, “non sequiturs” and reason that “compels” assume deductive logic. But science includes at least three types of reasoning: deductive, inductive, ampliative. Ampliative is also known as Inference to the Best Explanation (IBE).
Many believe that IBE is the most common and important form of reasoning used in science. Understanding how the eye evolved is an example of this type of reasoning in science.
To evaluate an instance of IBE, we have to look at both the explanation itself and the reason that is it best.
We can ask who the target for the explanation is, what level of explanation is being requested, what exactly is being explained, and what are the details of the explanation. Then we can ask about why it is best: what are the competitors and what are the criteria.
I have not read the book, but looking at the Amazon description and sample, it seems that the author was aiming to justify evolutionary explanations to a popular audience. So in reviewing the book with respect to that purpose, I would ask whether he discussed that nature of scientific reasoning and explanation and then why ID does or does not qualify as scientific explanation. Turning to the eye in particular, I would look for a review of the science which is suitable for a popular audience. I would want to see the author describe clearly what was to be explained, how the explanation worked, why it was best. Perhaps the author might address the various evolutionary mechanisms and how each could apply to steps in the evolution of the eye, although this may be more detailed then would suit his purposes.
I am not sure if your post was meant as a criticism of the book given its aims and audience or as a more general questioning of explanation in the sciences and how it applies to evolution of the eye. I do think the two possibilities need to be clearly separated when critiquing.
I’m not seeing it.
As best I can tell, Rogers is making a plausibility argument for the evolution of the eye, while you are complaining that he is only making a plausibility argument.
His argument is that it seems plausible to him?
I wonder where he says that in the book. It should probably be in the title.
Should have been abduction. Not ampliative, which also includes induction.
Hi everyone,
I wrote a short comment on the Peaceful Science thread, with links to some useful recent articles on the evolution of the eye.
It didn’t detract from your comments though. Good points!
Primarily how things are presented to the public. He says this is what he teaches his students. I am only focusing on his argument about how eyes evolved but wanted o make sure I didn’t leave out the fact that his argument also includes an appeal to common descent.
I need to explore whether his argument for common descent supports his scenario for how the eye evolved. So still some work to do.
Want to make it cl;ear that I am trying to evaluate the argument, not argue over whether or not eyes evolved.
I do want to explore why someone not named Rogers would think his scenario is plausible.
ETA: From what I have gathered so far he is not presenting has argument as an IBE.
Yes, but I don’t think that’s what he means, or he means more than that. I’ll give that some thought. I mean if it’s just moving alleles around drift can do that. Wouldn’t one need a positive reason or some evidence to attribute it to selection?
Mung,
Alleles moving around seems uninteresting and almost meaningless to me, until we know where the heck the alleles come from to begin with. I mean, an allele pops up for a tear duct in the corner of an eye, come on.
To argue whether or not that has a selective advantage and if that would cause all those who don’t get the lucky accident to die off? I think we are already into the late chapters of ludicrous story telling, how does one even start to believe the fist half of this book, before we get to more yarns.
The paper you site from Nilsson, of the Nilsson Pelger nonsense, just appears to be another rehash of the idea that “having a better eye sure would have been useful, and so that’s how it got here.”
Not informative in the least in my opinion. I am not sure what you learned that was new from it.
All that eyes do is twist images into manageable pieces that can ride the optic nerve into the skull. Then the memory takes over.
All eye problems, 98% or so, are from outside the skull. tHis because there is no machinery to break down inside the skull. outside its zillions of skrewups.
NEVERTHELESS all that biology must do is develop the outside machine the eye.
A YEC chas problems here. We do see only two or three types of eyes in nature.
Yet there are varieties at the order of simplicity.
There is a need to explain eyes poping out here and there. My favorite example is the tuataras which has eyes on top of its head. yet it would not have been this way on creation week. therefore it came afterwards by innate biology mechanisms.
eyes must be able to develop and change as needed.
its impossible by evolving steps that have no purpose in mind.
half a eye is not going to be selected on surely.
The eye makes evolution very inplausible.
Nobody claims that is what happened. But we’ve been over that.
Also you don’t seem to understand what at allele is. There is no such thing as an “allele for a tearduct”. Alleles are different mutant versions of the same gene. They can be something like a gene, and another version of the same gene with as little as one single nucleotide substitution mutation in it.
You seem to think there was something like an organism like a human walking around, and then this human has a child, and the child has a mutation that gave it a tearduct that the parent didn’t have. That’s not how it works. Nobody claims this is how it works, and if you have been led to believe this is how it works you have been misinformed.
phoodoo,
Yes, an end to ludicrous story telling, I say. Some bloke in the sky did it.
His mistake if so.
If you are going to write a book about the evidence for a scientific theory x, you probably need to understand how evidence works in science, explain that to the reader, and then explain how any examples you present meet those criteria.
If he really thinks that science “proves” evolution in the mathematical/deduction sense of proof, then his book is going to be flawed from the start.
Nobody claims how it works.
The essential idea is very simple: reiterative rounds of variation (mutations and other genomic changes) and selection (differential breeding success in a particular environment).
And there is no alternative scientific explanation that better fits the facts or that has more predictive power.
Don’t you have something more productive you could be doing? How are you on your prayers this week? Done your hours have you?
I encourage people like you to pray, as often as you can for as long as you can.
I would start a thread “The origin of the Eye according to phoodoo” but we all might as well just go and re-read the “How decisions are made in phoodoo’s world” thread, it’ll be exactly the same.
I will only say you are wrong, but I will never say what is right
Well, that sure sounds like an allele for a tear duct popping up in the corner of an eye, and it being selected for Alan.
I know it sucks to have to come to terms with your own theory.
If a moistened eye you seek
Design is your sole technique:
Only blokes up in the sky
Can build the means to wet an eye.
Allan Miller,
Much more plausible than accidents.
Mung,
I wanted to write something here, but I cannot choose where to start. I’m giving it a try, but I found your complains a bit strange.
For example, you complain that if it’s not Darwinism, then why would this guy mention what Darwin wrote. You seem to think that just by mentioning Darwin the whole of evolutionary theory, as it stands today, was exactly and nothing else but what Darwin proposed.
I don’t get this. Evolutionary theory has developed well beyond Darwin. That doesn’t mean that we’re committed to ignore the beginnings of the theory, or the evidence presented by anybody before, say, the development of molecular genetics. After all, Darwin started this thing, and wrote a large volume with a variety of observations, besides leaving a rich collection of letters, and other books. Are you saying that, in order for this not to be Darwinism Darwin has to be completely ignored? That we should never ever mention anything he tried to figure out, or any examples he might have provided?
Then you seem to have missed the point of the eyes example. The very guy says he’s talking about showing that the evolution of the eye is feasible. I don’t see anything wrong with that. When we see a human eye, it’s very hard to conceive how it could evolve. From what? What good is half an eye? (as creationists would say). Creationists love quoting Darwin’s paragraph introducing the issue (does this quoting mean they’re Darwinists too?), where he said that it looks like a ridiculous proposition. What they forget to mention is the following paragraphs talking about the feasibility of eye evolution, given that there’s eyes at many levels of complexity that are useful to the organisms that have them. That demonstrates that there’s paths towards complex eyes from simpler eyes. It demonstrates that these eyes are useful to the organisms that have them too. Therefore the evolution of the complex eye doesn’t look ridiculous anymore.
That’s the point, and it’s the same point Roberts (or whomever), is trying to present. That there’s a path towards a complex eye, and, therefore, that it’s feasible for complex eyes to evolve from simpler ones.
Of course, that doesn’t prove that they evolved. Of course that doesn’t prove that their evolution is due to natural selection, or to mutations. But it shows that there’s a path. Distracting yourself with how much it proves or doesn’t prove constitutes nothing else but missing the point, again, that there’s potential evolutionary paths towards complex eyes from simpler eyes.
To tackle the rest, going from it’s feasible to this is the history of the human eye, or of the octopi eyes, etc, it’s still much more work to be done, but, as a beginning, talking about the feasibility, about how we can observe diverse eye complexities in nature, seems like an excellent start towards deciphering the issue. If we could not even show that it’s feasible, then why would we go on?
Science advances in steps. Scientists look for one angle, then another, then another. One answer often results in more questions. There’s nothing wrong in presenting but the start in the solution of a problem. Actually, I think that’s the best way to present scientific themes. I prefer for people to understand that it’s an ongoing process, that sometimes a single piece of evidence indicates a direction, where to follow on for further clues, the new questions to answer in a quest to understand. After all, science is not magic. It’s not a one step endeavour. it’s not merely presenting a couple premises and following towards the conclusions. Nope. It’s a process that includes many stages.
Anyway, hopefully this helps.
phoodoo,
I just wonder what you think you accomplish by demonstrating such unwillingness to understand. Do you think I’ll read and say, “gee, this guy doesn’t want to even try and understand, therefore god-did-it.”?
I think it has already been pointed out that genes do not map structures on a one-to-one basis. The body grows from an embryo, not a blueprint. There’s a whole branch of biology, evo-devo, devoted to the subject.
And it’s amazing how cats have holes in their fur just where their eyes are.
How do you know this, not having your own theory?
…but Iberian moles don’t.
Your link is broken, Charlie. Though you make a good point about the defective development of Spanish Mole eyes.
Yes, but the meme that Swamidass and his acolytes are trying to spread over there at Peaceful Science is that Darwinism is dead. So any time I have an opportunity to point out that Darwinism is not dead I take it. So while my comment may seem out of place, given the general context over there I hope that helps it now make sense to you.
Thanks, I’ve fixed it.
And you will see from it that they aren’t defective.
Doesn’t it also demonstrate that there is a path from complex eyes to simple eyes, and in fact, from any kind of eye to any other kind of eye? If not why not?
Is it plausible that given the complex vertebrate eye, it could eventually evolve into just a light sensitive spot, using the same line of reasoning?
ETA:
Then it’s feasible that simpler eyes evolve from complex eyes. True?
CharlieM,
No. I should have said degenerate. On the other hand, this paper talks about defective lens development in Spanish Moles.
And here’s a paper looking at convergent evolution comparing morphologies and sequence similarities to various mammal groups that have taken to a subterranean lifestyle.
Certainly non-functional, degenerate eyes have evolved from functional eyes. See the paper I linked to.
So just in the way of a more general comment. We look around at all the organisms alive today and try to place them in order from “simple” to “complex.” Then we say therefore, it is plausible that there is an evolutionary path from any one simpler organism to any one more complex organism via the “intermediate” organisms.
Would anyone buy that?
And of course it’s equally plausible that any organism in the “simper” category could have evolved by a pathway from one of the “complex” organisms by a pathway consisting of the organisms of “intermediate” complexity.
If it’s not plausible for organisms, why is it plausible for organs, such as the eye?
So you think it plausible that one day it will “degenerate” into a simple light-sensitive spot?
Well, life started out simple. And mutations lead to innovations. The chance to exploit new niches. And there has to be a plausible path from each extant organism (and all extinct ones) back to the universal common ancestor for evolution to be true. That’s a big target to shoot at!
The working hypothesis fits the observed facts. There isn’t another one.
This is observed in parasites. Also viruses.
As it is quite plausible, we don’t have to worry.
Did you read the link Charlie posted? Fits the scenario.
Which only makes the problem even harder Alan.
Except for skeptics. Perhaps they have defective eyes that refuse to see.
Mung: Your point is correct. It reminds of the fact that arguments that statistical mechanics shows entropy almost always increases in the future also show that it almost always increases when moving to the past. So that whole egg most likely resulted from a broken one, according to bare SM!
Back to evolution. I think the book’s author made a mistake. The eye is not a good example of evidence for evolution if one’s goal is trying to prove evolution to someone who does not accept it.
The example of the eye usually comes up as an example of complexity that could not have evolved and is raised by the non-believer in evolution. So the counter argument to that is to claim that small steps can still work to lead to complex organs. Then the non-believer in evolution may say: “what use is an incomplete eye?” That’s when the examples of incomplete eyes in contemporary creature are useful..
[ETA: deleted stuff that may be incorrectly read as inappropriately attributing motives]
What do you really think this argument is about? What does ‘Darwinsim’ mean to Dr S and his biologist gang, do you think? Why do they see a hidden agenda (I think) iin people who use it with that meaning?
AFAIK, no physicists complain when the phrase “Newtonian mechanics” is used. But biologists don’t like “Darwinist evolution.”. Why do you think that is?
[ETA: deleted stuff that may be incorrectly read as inappropriately attributing motives]
Rather pleiotropy and regulator genes make the solutions elegant.
What are skeptics refusing to see? You seem remarkably reticent regarding other explanations for what we observe.
Organisms are seen to diversify from the general type to the specific due to the lifestyle which they adopt. Moles and blind cave fish are examples of this narrowing of the niches available to them. Degeneration is part of the process which allows evolution to move forward.
Everything from eye spots to fully developed vertebrate eyes are present in the various extant organisms. which goes to show that there is a progression and some organisms have stopped short of their full potential. So we witness degeneration and a stopping short of further evolution.
Oh, that should make your accidents even more fortuitous. Ha!
Not sure about that. When life first got going on Earth, there were many empty niches to fall into. Now, life of some kind seems to occupy any available niche. So specialists become ever more closely adapted to the niche they occupy until that niche disappears or changes too rapidly for adaptations to keep pace. Then that specialist goes extinct, opening an opportunity to another species to exploit that empty niche.
They are stuck on a local fitness peak. 🙂
So what this reminds me of is that we need to say something about why all eyes did not get more complex in all lineages. If natural selection brings about complex eyes, why are all eyes not complex?
It just happened that way I guess. 😉
Dr. S. posted a definition, I’ll see if I can dig it up. But I think it boils down to a claim that IDists think all evolution is adaptive. And I think that’s a straw-man.
Whatever their motives are, I am sure they are pure.
But thanks to natural selection those “simple” eyes are fully functional and complete. Are they not?