106 thoughts on “A complex adaptation: the eye”

  1. Mung: 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?

    Remember the niche, mung, remember the niche. The niche is the designing element. If the niche is light-absent, there is no adaptive advantage in possessing a visual system.

  2. Alan Fox: Not sure about that. When life first got going on Earth, there were manyempty 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.

    You imagine an early earth from a position as if there were humans with their twenty-first century senses and understanding looking on at it. And those humans would have seen that life proceeded by means of chance beneficial mutations being selected. I’m not willing to make such speculations. And even if your understanding of an early earth where life was sparse was true, don’t you think that generalists would be more likely than specialists to survive and prosper?

    And what is your definition of ‘niche’ It seems to me it can be anything from a single host organism to the world ocean, from eating leaves from a single plant species to eating anything that is organic. So we seem to have general niches and speciality niches.

    It’s no use there being a niche if an organism does not have the necessary equipment to exploit that niche.

  3. Alan Fox: If the niche is light-absent, there is no adaptive advantage in possessing a visual system.

    Doesn’t matter if there is an adaptive advantage if you don’t get the right lucky accidents in the right order first.

    That’s an awful lot of accidents.

  4. CharlieM: It’s no use there being a niche if an organism does not have the necessary equipment to exploit that niche.

    Just wait for more accidents Charlie.

    Eventually a tear duct will hit you right in the eye, just when you need it most.

  5. Mung: 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.

    And I would say that the most successful organisms in a Darwinian sense are the ones without eyes 🙂

  6. Alan Fox: 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.

    That idea sounds as if it should be called “Niche Platonism.”

  7. CharlieM: You imagine an early earth from a position as if there were humans with their twenty-first century senses and understanding looking on at it.

    No, I don’t. I imagine the early Earth as devoid of humans altogether.

    And those humans would have seen that life proceeded by means of chance beneficial mutations being selected. I’m not willing to make such speculations. And even if your understanding of an early earth where life was sparse was true, don’t you think that generalists would be more likely than specialists to survive and prosper?

    Less diversity, certainly. Sparseness? Life must have started somewhere, so logically elsewhere than that somewhere, life was non-existent. Very different from today.

    And what is your definition of ‘niche’ It seems to me it can be anything from a single host organism to the world ocean, from eating leaves from a single plant species to eating anything that is organic. So we seem to have general niches and speciality niches.

    A niche is the immediate environment that a species occupies. I believe there is an organism whose sole habitat is human eyelash follicles.

    It’s no use there being a niche if an organism does not have the necessary equipment to exploit that niche.

    That makes no sense. There can be niches that are empty.

  8. CharlieM: And I would say that the most successful organisms in a Darwinian sense are the ones without eyes

    Those that reproduce are the most successful whether they have eyes or not.

  9. phoodoo: Just wait for more accidents Charlie.

    Eventually a tear duct will hit you right in the eye, just when you need it most.

    Or wait for the designer to release ver 2.5.

  10. Alan Fox: The niche is the designing element.

    A bit too simple.

    There is an interplay between niche and population. The population is involved in shaping the niche and the niche is involved in shaping the population.

  11. Alan Rogers at PS:

    There is one more piece to the argument, which didn’t make it into my book. If the vertebrate eye did evolve, then it must have evolved by natural selection, because no other evolutionary force is capable of assembling a complex adaptation.

  12. CharlieM: It’s no use there being a niche if an organism does not have the necessary equipment to exploit that niche.

    But if through natural variability you have just a little better equipment than somebody else to exploit it, you generally leave more offspring. Rinse and repeat.

  13. CharlieM: And I would say that the most successful organisms in a Darwinian sense are the ones without eyes

    But they might still have a light sensitive spot. 🙂

  14. Alan Fox: Remember the niche, mung, remember the niche. The niche is the designing element. If the niche is light-absent, there is no adaptive advantage in possessing a visual system.

    You’ll have to do better than that. All these organisms have eyes. They are all in a “niche” where light is present.

  15. phoodoo: Just wait for more accidents Charlie.

    Eventually a tear duct will hit you right in the eye, just when you need it most.

    What about my other eye? 🙂

  16. Alan Fox:

    CharlieM: You imagine an early earth from a position as if there were humans with their twenty-first century senses and understanding looking on at it.

    No, I don’t. I imagine the early Earth as devoid of humans altogether.

    So it would be devoid of colours, shapes, smells, sound?

  17. Alan Fox:

    CharlieM: And even if your understanding of an early earth where life was sparse was true, don’t you think that generalists would be more likely than specialists to survive and prosper?

    Less diversity, certainly. Sparseness? Life must have started somewhere, so logically elsewhere than that somewhere, life was non-existent. Very different from today.

    Or equally speculative, life was more etherial, far less likely to leave any trace. Only when life forms became more dense did they begin to leave fossil evidence.

  18. Mung:
    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?

    That might also be inferred, but the question was about the evolution of complex ones. I doubt that too many people have trouble questioning if eyes could become simpler.

    It would be beautiful to find some examples of eyes evolving “backwards,” other than being lost in cave-dwelling organisms.

  19. Alan Fox:

    CharlieM: And what is your definition of ‘niche’ It seems to me it can be anything from a single host organism to the world ocean, from eating leaves from a single plant species to eating anything that is organic. So we seem to have general niches and speciality niches.

    A niche is the immediate environment that a species occupies. I believe there is an organism whose sole habitat is human eyelash follicles.

    So it is like I said. The niche for airborne microbes, black rats and the organism you mention above are very different in their limits.

    It’s no use there being a niche if an organism does not have the necessary equipment to exploit that niche.

    That makes no sense. There can be niches that are empty.

    Yes but if there are niches that can’t be used by organisms then they are of no use to organisms.

  20. newton: Those that reproduce are the most successful whether they have eyes or not.

    That is certainly true within species. Is it possible to measure success between species?

  21. CharlieM:Or equally speculative, life was more etherial, far less likely to leave any trace. Only when life forms became more dense did they begin to leave fossil evidence.

    Yeah. Because “life must have started somewhere” is as speculative as “Life was more ethereal as it condensed from a higher dimension archetype”

    GTFO

  22. Mung: Alan Rogers at PS:

    There is one more piece to the argument, which didn’t make it into my book. If the vertebrate eye did evolve, then it must have evolved by natural selection, because no other evolutionary force is capable of assembling a complex adaptation.

    </blockquote

    How can natural selection alone assemble anything?

  23. newton:

    CharlieM: It’s no use there being a niche if an organism does not have the necessary equipment to exploit that niche.

    But if through natural variability you have just a little better equipment than somebody else to exploit it, you generally leave more offspring. Rinse and repeat.

    So those that leave more offspring are more successful?

    But when I said that the most successful organisms in a Darwinian sense are the ones without eyes, You said

    Those that reproduce are the most successful whether they have eyes or not.

    I think we need some clarification here. Which do you think are the most successful the golden mole or the house mouse or are they equally successful?

  24. dazz: Yeah. Because “life must have started somewhere” is as speculative as “Life was more ethereal as it condensed from a higher dimension archetype”

    GTFO

    All our observations tell us that life comes from life. Of course if you wish to believe in spontaneous generation feel free.

  25. CharlieM:
    So those that leave more offspring are more successful?

    Within a species’ population sure. But reproduction is not the only measure of success “between” already diverged populations occupying different niches, even if geographically co-located. member of a single ecosystem, like some plants and the animals that eat them, then it depends on the equilibrium between how much each reproduces. Too many herbivores would eat off the food and commit unadverted suicide. So, it’s not as simple as saying, gee, if you reproduce a lot you’re evolutionarily successful. It’s whether the lineage continues that makes it a successful lineage.

    CharlieM:
    But when I said that the most successful organisms in a Darwinian sense are the ones without eyes, You said

    I don’t know if that’s the “Darwinian sense.” Again, it’s not that simple. We simplify a lot in order to get started understanding, but, in the end, successful in the evolutionary sense (if that’s what you meant by Darwinian sense), means that the lineage continues. Unsuccessful means that the lineage is either extinct, or will go extinct if things continue the way they’re going.

    So, for example, a parasite that kills its host will go extinct unless there’s at least a few individuals in the population that will survive and still feed the parasite, which means that at some point there will be an equilibrium between the number of parasites and the number of individuals that can bear them, grow them, but not die because of them.

    Anyway, more to your point, I think that many organisms outnumber and can reach equilibrium better than other life forms, and that, effectively, in the long run, organisms without eyes might be more successful in leaving continuing lineages than organism with eyes. But I could be wrong.

  26. CharlieM: How can natural selection alone assemble anything?

    It can’t. Which is why I told Rumraket that I think by “natural selection” Rogers has more in mind than simple changes in allele frequencies in a populaton.

  27. Mung:
    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?

    Because “natural selection” is but a metaphor for organisms being immersed in some environment where more complex eyes may or may not be advantageous. Because it also depends on whether the advantage might lie somewhere other than in more complex eyes. When we think about evolution we’re not thinking of a magical infallible being, let alone one who wants to produce something specific, like life forms with a single kind of eye. it all depends on the interplay of many factors, including the life forms involved.

  28. Mung: 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.

    Yes but with new mutants that presumably start at a very low frequency in the population the probability of fixation through random sampling is very low. It’s not that it’s impossible and never happens, but it is much more likely that selection is what drives alleles to fixation if and when they have some adaptive benefit than it is that they rose to fixation through drift.

    When it comes to explaining the eye as a complex adaptation, while it is theoretically possible every historical gradation in the evolution of the vertebrate eye was fixed by genetic drift, it is a much more plausible explanation that selection was the mechanism responsible. After all, the eye is an extremely powerful adaptive trait.

    Given even tiny differences in effect on average reproductive success, with a large population such alleles are almost guaranteed to rise to fixation.

    Suppose some mutation has the effect of increasing the average reproductive success on carriers by 0.03%. The allele initially exists in only 0.01% of the population, but the population has an effective size of 1 billion individuals.

    I think here we can use the diffusion-approximation for the probability of fixation of a beneficial allele from Joe Felsenstein’s Theoretical Evolutionary Genetics, page 315 equation (VII-91):
    U(p) \simeq \frac{1-e^{-4Nsp}}{1-e^{-4Ns}}

    With
    p=0.00001
    n=10^9
    s=0.003

    I get U(p) = 0.9999938557876 probability of fixation, which is pretty close to 1. I hope I’m not using this equation incorrectly. I’m sure Joe will weigh in if I am.

  29. phoodoo:
    Allan Miller,

    Much more plausible than accidents.

    So the observed fact that mutations happen and affect the physiology and adaptive traits of the organism, is less plausible than the unobserved fantasy that a mind living in the absence of a physical brain, can manipulate matter without a physical body, and simply WISH it into existence?

    I’m going to go ahead and not take your intuitions about what is plausible seriously.

  31. Rumraket,

    An effective size of a billion would be *huge*!

    CharlieM: All our observations tell us that life comes from life. Of course if you wish to believe in spontaneous generation feel free.

    All our observations tell us that life comes from life, so ‘spontaneous generation’ is out? But somehow, invisible designers and wibbly crystallisation from a Higher Plane are still in the game?

  32. All our observations also tell us that life is made of atoms, and that life comes from life by cell division. But those two observations completely undermine the conclusion CharlieM is seeking to make by just couching it in terms of “life comes from life”. I suppose we now have to posit an infinite regression of dividing cells.

  33. Allan Miller:
    Rumraket,

    An effective size of a billion would be *huge*!

    Yeah I have mistakenly used census population size as effective population size, which I now learn are two completely different things.

  35. Mung: But thanks to natural selection those “simple” eyes are fully functional and complete. Are they not?

    As Neil and Alan have discussed, “Fully functional” has meaning only wrt to success in the organisms niche.
    That’s basically Eric H’s problem as well.

    “Success” was addressed and partly defined by the 1970s version of the Bee Gees with their work being extension of some work by Nash which he did not publish until he joined the CSN&Y collaboration.

    Also interesting is work showing how Darwinism evolution can optimize energy expenditure for an organism in its niche.

    A book to add to the philosophy of biology shelf of your collection: A Critical Overview of Biological Functions

  36. Mung: 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.

    I think the debate is really about whether the other side is arguing in good faith when it uses the word ‘Darwinism’.

    As best I can tell, crusading scientists fear anti-evolutionists use the word as the first step in refuting strawmen versions of modern science. Their opponents think that scientists reject or hide key aspects of their theory or its historical context.

    Nobody much cares about crackpots trying to apply thinking shaped by the Newtonian mechanics of everyday life to the reality of GR and QM.

    But there are political consequences to the ‘Darwinism’ debate: on education in particular and more generally on the role of science and expertise in society.

    That’s what the argument about ‘Darwinism’ is actually about.

  37. Neil Rickert: That idea sounds as if it should be called “Niche Platonism.”

    I hope you do not mind me saying so, but it seems to me that your debating points are falling into a dualist rut.

  38. Rumraket:

    When it comes to explaining the eye as a complex adaptation, while it is theoretically possible every historical gradation in the evolution of the vertebrate eye was fixed by genetic drift, it is a much more plausible explanation that selection was the mechanism responsible. After all, the eye is an extremely powerful adaptive trait.

    Mung:

    ETA: From what I have gathered so far he [Rogers] is not presenting has argument as an IBE.

    How Rogers should have written his book.

  39. CharlieM: That is certainly true within species. Is it possible to measure success between species?

    Sure, what are the objective criteria?

  40. Rumraket: When it comes to explaining the eye as a complex adaptation, while it is theoretically possible every historical gradation in the evolution of the vertebrate eye was fixed by genetic drift, it is a much more plausible explanation that selection was the mechanism responsible. After all, the eye is an extremely powerful adaptive trait.

    And each “historical gradation” MUST have arisen by a lucky accident. Even though you hate to admit it, this is a part of the theory of unguided evolution.

    How many lucky accidents do you think it took to get to the vertebrate eye we see today?

    These lucky accidents need to be very very common before we can even get to the process of sorting them.

  41. Mung:
    It can’t. Which is why I told Rumraket that I think by “natural selection” Rogers has more in mind than simple changes in allele frequencies in a populaton.

    Changes in allele frequency does not refer to natural selection, but to evolution. natural selection is one way in which allele frequencies change, but it is not the whole of the process(es).

  42. Rumraket:
    So the observed fact that mutations happen and affect the physiology and adaptive traits of the organism, is less plausible than the unobserved fantasy that a mind living in the absence of a physical brain, can manipulate matter without a physical body, and simply WISH it into existence?

    I’m going to go ahead and not take your intuitions about what is plausible seriously.

    I just had to quote this.

  44. So it appears to me that Rogers’ plausibility argument begs the question. It’s only plausible if one accepts the premise that natural selection can bring about something as complex as the vertebrate eye. But that is precisely what is in dispute.

  45. Entropy: CharlieM:
    So those that leave more offspring are more successful?

    Within a species’ population sure. But reproduction is not the only measure of success “between” already diverged populations occupying different niches, even if geographically co-located. member of a single ecosystem, like some plants and the animals that eat them, then it depends on the equilibrium between how much each reproduces. Too many herbivores would eat off the food and commit unadverted suicide. So, it’s not as simple as saying, gee, if you reproduce a lot you’re evolutionarily successful. It’s whether the lineage continues that makes it a successful lineage.

    So successful evolution requires cooperation and balance. Conflict and strife at a lower level helps to maintain the overall balance. We should not think of lions as being in conflict with wildebeest. They are beneficial as they help to maintain the health of the species.

    There is wisdom in the balance of nature. Individuals and species come and go but all this helps to maintain the viability and onward march of life as a whole. This in turn has allowed consciousness to make an appearance and to progress. And this progress goes hand in hand with the physical progress of complexity of senses such as eyes along with the nervous systems needed to interpret what the senses reveal.

    Surely everyone can see that the sequences from eye spot to vertebrate eye, and simple nerve ganglion to human brain, are progressions? If not then why do they call the visual apparatus of blind cave fish a regressive trait?

  46. Entropy:

    But when I said that the most successful organisms in a Darwinian sense are the ones without eyes, You said…

    I don’t know if that’s the “Darwinian sense.” Again, it’s not that simple. We simplify a lot in order to get started understanding, but, in the end, successful in the evolutionary sense (if that’s what you meant by Darwinian sense), means that the lineage continues. Unsuccessful means that the lineage is either extinct, or will go extinct if things continue the way they’re going.

    So, for example, a parasite that kills its host will go extinct unless there’s at least a few individuals in the population that will survive and still feed the parasite, which means that at some point there will be an equilibrium between the number of parasites and the number of individuals that can bear them, grow them, but not die because of them.

    Anyway, more to your point, I think that many organisms outnumber and can reach equilibrium better than other life forms, and that, effectively, in the long run, organisms without eyes might be more successful in leaving continuing lineages than organism with eyes. But I could be wrong.

    One thing we can say is that up ’till now life as a whole has successfully survived and continues to exist. And it has reached a stage where it not only exists but is now aware of its own existence. To me that is progress.

  47. Mung:
    So it appears to me that Rogers’ plausibility argument begs the question. It’s only plausible if one accepts the premise that natural selection can bring about something as complex as the vertebrate eye. But that is precisely what is in dispute.

    There’s no begging the question. In order to check if it’s feasible, there’s nothing wrong in asking what’s required if it were true that the eye evolved [by natural selection]. Well, for one thing, there should be attainable stages, each stage useful to its possessor. Lo and behold, there’s such a thing even among extant life forms. Therefore this could have evolved by steps. It seems at least plausible. The results could have been anything. No simpler eyes, simpler eyes that don’t look like they’d be potential precursors for more complex eyes, etc.; or that apparent stages exist, but they’re useless to their possessors (which would indicate that natural selection did not play a role, even if the eyes evolved), more etc.

  48. CharlieM: Surely everyone can see that the sequences from eye spot to vertebrate eye, and simple nerve ganglion to human brain, are progressions?

    Not I. I see them all as regressions from a perfect ideal. 😉

  49. Mung: So it appears to me that Rogers’ plausibility argument begs the question. It’s only plausible if one accepts the premise that natural selection can bring about something as complex as the vertebrate eye. But that is precisely what is in dispute.

    What is it about it you think is lacking in plausibility?

  50. phoodoo: And each “historical gradation” MUST have arisen by a lucky accident.

    You mean by mutation, sure.

    Even though you hate to admit it, this is a part of the theory of unguided evolution.

    I think it’s telling that you keep calling them “lucky accidents”. That’s of course a rhetorical device you employ to make it seem implausible. If it really was that implausible you wouldn’t have to come up with alternative and silly descriptions of the process of evolution.

    How many lucky accidents do you think it took to get to the vertebrate eye we see today?

    From what stage? Not that I claim to know regardless.

    When was the eye created and how? You want to know how many mutations happened in the evolution of the eye, and when, and what they did exactly, and even if you were given information to that effect you’d still find it pretty much impossible because you’d just call all the individual steps “lucky accidents”.

    But on zero evidence whatsoever you’d apparently swallow the idea that the eye was WISHED into existence by magic. You wouldn’t have different hypocritical double standards with respect to evidence and plausibility right?

    These lucky accidents need to be very very common before we can even get to the process of sorting them.

    Considering the eye has been evolving for something like 700 million years, how common is “very common”?

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