Sendraks wrote:Yeah, you've really failed to highlight any sort of problem with what I wrote there David.

If you are referring to your apparent recapitulationism, I have already mentioned that it is not very reliable.

I've already indicated that your comment runs counter to my own understanding. So no dice there I'm afraid.

For clarity I am not referring to recapitulation theory (long since discredited), although it is cute that David thinks I am and his misunderstanding probably stems from failing to understand what I wrote.

Sendraks wrote:For clarity I am not referring to recapitulation theory (long since discredited), although it is cute that David thinks I am and his misunderstanding probably stems from failing to understand what I wrote.

Then please post more cearly, because recapitulationism is the only sense I can make of your posts so far.

On the tuatara's third eye: there is no evidence that the third eye was ever a full-sized, "normal" eye, with an RPE layer and choroid, in spite of claims made on Wiki and by you (which don't even consider those things). My suspicion is that it always had a thin, protective layer of skin over it, and that the lens was not for imaging, but for concentrating the light onto a reduced-size retina.

DavidMcC wrote:

Sendraks wrote:For clarity I am not referring to recapitulation theory (long since discredited), although it is cute that David thinks I am and his misunderstanding probably stems from failing to understand what I wrote.

Then please post more cearly, because recapitulationism is the only sense I can make of your posts so far.

Then I would suggest that your understanding of recapitulationism is flawed and you'd do well to refresh your understanding of it.

DavidMcC wrote:On the tuatara's third eye: there is no evidence that the third eye was ever a full-sized, "normal" eye, with an RPE layer and choroid, in spite of claims made on Wiki and by you (which don't even consider those things).

It would appear that you have again, failed to understand what I wrote. Because what you are saying I have "claimed" here, is demonstrably factually incorrect as this post attests.

http://www.rationalskepticism.org/evolution/birds-possibly-developing-selfconcious-brains-t52176-320.html#p2417545

DavidMcC wrote:My suspicion is that it always had a thin, protective layer of skin over it, and that the lens was not for imaging, but for concentrating the light onto a reduced-size retina.

So, working from your "suspicion" in a way that is consistent with the theory of evolution, what would you conclude about the functional state of all three eyes on tuatara ancestors?

I've seen evidence for neither position. But I have seen evidence for a system with three eyes persisting for hundreds of millions of years despite protestations that more than two eyes are cost-prohibitive. Nobody said anything about the more than two eyes being equivalent to more than two fully functional vertebrate eyes until DavidMcC shifted the goalposts. As we're talking about hypothetical life on other worlds, there was never any reason to invoke specific types of terrestrial eyes. Meanwhile, DavidMcC's assertion that eyes like ours are necessary for longer-lived sapients which don't eventually go blind is lacking in the following two ways:

1) He hasn't supported his assertion from the terrestrial standpoint.
2) Nobody ever said that sapients need to be particularly long-lived. It would be unfortunate for sapience to evolve in an organism which could both comprehend the inevitability of its death and would also see it coming up very quickly, and I've no idea what that would do to their culture, but there isn't any rule that sapients must live for a very long time.

ScholasticSpastic wrote:
2) Nobody ever said that sapients need to be particularly long-lived. It would be unfortunate for sapience to evolve in an organism which could both comprehend the inevitability of its death and would also see it coming up very quickly, and I've no idea what that would do to their culture, but there isn't any rule that sapients must live for a very long time.

Also, we sapients are not especially long lived. Even removing the distortion of average human lifespans that resulted from historically high infant mortality rates until the modern era, Human beings only clocked in a staggeringly unimpressive 40-45 years (male) and 30-35 years (female).

And then let's not forget that we haven't determined that the reparation mechanisms of the vertebrate eye are the only possible reparation mechanisms evolution may have come up with anywhere. So even a more complex eye that's worth hanging onto for the rest of a relatively long life of 45 years needn't necessarily cost as much as one of our eyes. It could cost more or it could cost less, depending on the mechanism, the relative size of the rest of the sapient's energy budget, and the fitness advantage conferred by having some number and arrangement of those eyes.

Sendraks wrote:

ScholasticSpastic wrote:
2) Nobody ever said that sapients need to be particularly long-lived. It would be unfortunate for sapience to evolve in an organism which could both comprehend the inevitability of its death and would also see it coming up very quickly, and I've no idea what that would do to their culture, but there isn't any rule that sapients must live for a very long time.

Also, we sapients are not especially long lived. ...

I never said that humans had to be especially long lived, Sendraks. Why are you even making that point (which I do not deny)? It seems to be irrelevant, because I am not trying to argue that intelligence is proportional to longevity without reference to the species (which would be an absurd claim).

DavidMcC wrote:
I never said that humans had to be especially long lived, Sendraks. Why are you even making that point (which I do not deny)? It seems to be irrelevant, because I am not trying to argue that intelligence is proportional to longevity without reference to the species (which would be an absurd claim).

Well I was responding to what SS said and within the context of what SS said, it was an entirely relevant point to make. And SS was responding to your earlier comment to the effect of..

DavidMcC wrote:does not disprove my case that the surface vertebrate eye ENABLES a long life without going blind.

...and in the case of humans, the eye clearly does not enable a particularly long life.

ScholasticSpastic wrote:I've seen evidence for neither position. But I have seen evidence for a system with three eyes persisting for hundreds of millions of years despite protestations that more than two eyes are cost-prohibitive. Nobody said anything about the more than two eyes being equivalent to more than two fully functional vertebrate eyes until DavidMcC shifted the goalposts. As we're talking about hypothetical life on other worlds, there was never any reason to invoke specific types of terrestrial eyes. Meanwhile, DavidMcC's assertion that eyes like ours are necessary for longer-lived sapients which don't eventually go blind is lacking in the following two ways:

1) He hasn't supported his assertion from the terrestrial standpoint.

Nonsense. I think you misconstrue my claim, which has to do with how the VERTEBRATES (NOT JUST HUMANS) evolved a solution to the photo-oxidative damage problem which did not suffer from the disadvantages of the various invertebrate solutions, which were OK for them, but not for vertebrates.

2) Nobody ever said that sapients need to be particularly long-lived. It would be unfortunate for sapience to evolve in an organism which could both comprehend the inevitability of its death and would also see it coming up very quickly, and I've no idea what that would do to their culture, but there isn't any rule that sapients must live for a very long time.

I never said there was a rule that we should live a particularly long time. But name an invertebrate that lives a long time in broad daylight, and has high res. eyesight.
If it helps yopu understand my claim, you should think about invertebrate eyes, and how they evolved their own way round the problem of living for decades without going blind. I found verious basic solutions, and I will re-list the main ones here just for you:
1. Hunting spiders: the entire retina is destroyed and re-generated on a daily basis, with fresh opsins;
2. Queen ants (of various species): Stay in a dark, underground chamber for most of your life, just laying eggs, most of which hatch out into short-lived workers, who service your needs. (Please don't bother about the exceptions here, because I don't want to "write the book" again!)
3. Some lobsters: have simple, stalk eyes that regularly break off and are replaced fairly quickly.
4. 13-year and 17-year cicadas: stay underground as a larva for nearly all your life, only come abover ground to breed and die.
5. Shallow-water squid, most insects: Die young, just after mating.

I'm sure there are others, but that will have to do for now.

Sendraks wrote:

DavidMcC wrote:
I never said that humans had to be especially long lived, Sendraks. Why are you even making that point (which I do not deny)? It seems to be irrelevant, because I am not trying to argue that intelligence is proportional to longevity without reference to the species (which would be an absurd claim).

Well I was responding to what SS said and within the context of what SS said, it was an entirely relevant point to make. And SS was responding to your earlier comment to the effect of..

DavidMcC wrote:does not disprove my case that the surface vertebrate eye ENABLES a long life without going blind.

...and in the case of humans, the eye clearly does not enable a particularly long life.

Obviously., the word "enables" is being interpreted by you to mean "forces", but that was not what I intended. Perhaps I should have said "gives the potential for a long life, in the absence of other life-span limiting factors", OK?

DavidMcC wrote:

ScholasticSpastic wrote:I've seen evidence for neither position. But I have seen evidence for a system with three eyes persisting for hundreds of millions of years despite protestations that more than two eyes are cost-prohibitive. Nobody said anything about the more than two eyes being equivalent to more than two fully functional vertebrate eyes until DavidMcC shifted the goalposts. As we're talking about hypothetical life on other worlds, there was never any reason to invoke specific types of terrestrial eyes. Meanwhile, DavidMcC's assertion that eyes like ours are necessary for longer-lived sapients which don't eventually go blind is lacking in the following two ways:

1) He hasn't supported his assertion from the terrestrial standpoint.

Nonsense. I think you misconstrue my claim, which has to do with how the VERTEBRATES (NOT JUST HUMANS) evolved a solution to the photo-oxidative damage problem which did not suffer from the disadvantages of the various invertebrate solutions, which were OK for them, but not for vertebrates.

Nonsense. You have not supported your claim that the parietal eye was never more than rudimentary. Sendraks has not not supported his claim that the parietal eye may at one time have been more than rudimentary. Both possibilities, however, are insufficient to show that (another of YOUR unsupported claims) two eyes are so expensive that we cannot afford additional eyes because we have living examples, and hundreds of millions of years of retention of the trait. A rudimentary eye is still an eye, and so demonstrates that an organism can well afford two fully developed vertebrate eyes PLUS at least one rudimentary eye. You are the one who keeps insisting on framing things in terms of fully developed vertebrate eyes. You haven't demonstrated any reason to so insist.

2) Nobody ever said that sapients need to be particularly long-lived. It would be unfortunate for sapience to evolve in an organism which could both comprehend the inevitability of its death and would also see it coming up very quickly, and I've no idea what that would do to their culture, but there isn't any rule that sapients must live for a very long time.

I never said there was a rule that we should live a particularly long time. But name an invertebrate that lives a long time in broad daylight, and has high res. eyesight.
If it helps yopu understand my claim, you should think about invertebrate eyes, and how they evolved their own way round the problem of living for decades without going blind. I found verious basic solutions, and I will re-list the main ones here just for you:
1. Hunting spiders: the entire retina is destroyed and re-generated on a daily basis, with fresh opsins;
2. Queen ants (of various species): Stay in a dark, underground chamber for most of your life, just laying eggs, most of which hatch out into short-lived workers, who service your needs. (Please don't bother about the exceptions here, because I don't want to "write the book" again!)
3. Some lobsters: have simple, stalk eyes that regularly break off and are replaced fairly quickly.
4. 13-year and 17-year cicadas: stay underground as a larva for nearly all your life, only come abover ground to breed and die.
5. Shallow-water squid, most insects: Die young, just after mating.

I'm sure there are others, but that will have to do for now.

I don't see how this helps support your earlier insistence that eyes are too expensive for hypothetical alien sapients to afford more than two of them. It appears to argue counter to that.

Also, I don't see how terrestrial examples get us very far when dealing with hypothetical extraterrestrials on planets which differ from ours. Nor do I think a sapient need necessarily be diurnal or surface-dwelling, though in the case of bird-like aliens, a burrowing habit probably rules out wings. There are plenty of crepuscular and nocturnal flying critters, though, for which light damage would be much less of an issue than you're making it. Nocturnal and crepuscular activity are not the only means by which a complex, long-lived organism can protect its eyes from light damage without investing in expensive repair mechanisms.

Finally, complex eyes are not necessarily going to pair with sapience. Vision is nice, but it's not the only way to detect trouble coming, and there's no reason to rule out lineages which are reliant upon other types of perception at a distance when we're considering possible sapients.

DavidMcC wrote:
Obviously., the word "enables" is being interpreted by you to mean "forces", but that was not what I intended. Perhaps I should have said "gives the potential for a long life, in the absence of other life-span limiting factors", OK?

Obviously your irony meter has been broken for a very long time, as you obviously like to accuse of others of misrepresenting your arguments while doing the very same thing. All while being so obviously condescending about it. (Obvious eye-roll of a plural and rudimentary sort, which allows me to afford multiple pairs of rolling eyes.)

Actually my claim, such as it is, is that to be consistent with evolution all three eyes would at one point been equally rudimentary. The possibility of the third having more function then degrading, seems unlikely to me but was included for completeness.

Sendraks wrote:Actually my claim, such as it is, is that to be consistent with evolution all three eyes would at one point been equally rudimentary. The possibility of the third having more function then degrading, seems unlikely to me but was included for completeness.

I am sorry that I misrepresented your claim. I shall endeavor not to do that again.

Not really any way to support such a claim either way, though. Eyes fossilize notoriously poorly.

Indeed. I don't claim to have any evidence either way, just that one approach is more consistent with wvolution than the other.

ScholasticSpastic wrote:

Sendraks wrote:Actually my claim, such as it is, is that to be consistent with evolution all three eyes would at one point been equally rudimentary. The possibility of the third having more function then degrading, seems unlikely to me but was included for completeness.

I am sorry that I misrepresented your claim. I shall endeavor not to do that again.

Not really any way to support such a claim either way, though. Eyes fossilize notoriously poorly.

Yeah, and I hope you two are going to withdraw your case against me over your claim that there must have been three identical, fully vertebrate eyes in an ancestral tuatara!
I sustopect that any ancestor with three eyes the same would be way pre-vertebrate, and the eyes woud not be vertebrate-type, but much simpler.
Your best case for a 3-eyed vertebrate is the lamprey, which has two almost fully vertebrate lateral eyes, focussed on infinity, plus a reduced-size, forward-facing eye, focussed at short range, and only used when homing in on the prey. I wrote a thread on the lamprey years ago, but I won't bother to dig it out unless you insist.