Freethought & Rationalism Archive

pz · 10-14-2002, 06:22 AM

Quote:

Originally posted by Zetek:
You assume that these fish depend upon sight for reproduction.

This is also rather ironic, considering that despite being highly visual animals, generations of prudish fundamentalists have managed to reproduce while only doing the deed in the dark.

Blinn · 10-14-2002, 06:27 AM

rebelnerd · 10-14-2002, 06:46 AM

Quote:

Originally posted by pz:

This is also rather ironic, considering that despite being highly visual animals, generations of prudish fundamentalists have managed to reproduce while only doing the deed in the dark.

<img src="graemlins/notworthy.gif" border="0" alt="[Not Worthy]" />

Filo

Nialler · 10-14-2002, 07:37 AM

I've just trawled through 7 pages which were alternately enlightening and deeply frustrating.

Am I the only one to perceive the irony inherent in a discussion about a being which has evolved to a state when it does not need to see, said discussion taking place with its precise human conterpart?

pz · 10-14-2002, 08:55 AM

Quote:

Originally posted by Nialler:
Am I the only one to perceive the irony inherent in a discussion about a being which has evolved to a state when it does not need to see, said discussion taking place with its precise human conterpart?

The analogy goes even deeper. We've been discussing an organism in which a portion of the brain expanded embryonically, only to contact an unresponsive, damaged environment, leading to a loss of potential and a regression of the neural tissue to a rudimentary state.

We've also been discussing the development of the eyes of the blind cave fish.

Blinn · 10-14-2002, 02:22 PM

Quote:

Originally posted by Doubting Didymus:
If we can back the conversation up a bit, I would like to ask vander a simple question, not to prove any point but only for information.

Vander, I am not sure what you are taking issue with. I think that everyone is talking past one another, and the issue is getting confused.

There are two main points involved here, so specifically, I would like to know what are you taking issue with.

Is it: That non-functioning, useless eyes exist? (that is, you acknowledge that eyeless cave dwellers exist, but you do not think that they do, in fact, have useless vestigial eyes).

Or, given that nonfunctional eyes exist, do you not accept that the organism would be improved by removing them.

Put simply, do you think that no vestigial eyes exist, or is it only the idea that they constitute bad design that you take issue with?

I think that clearing this issue up will facilitate further conversation.

I'd also like to know where Vanderzyden stands on this.

Blinn · 10-14-2002, 02:58 PM

Quote:

Originally posted by scigirl:

To Oolon or anyone else - does anyone know much about the embryological development of these vestigal eyes? That would be pretty convincing evidence - IMHO - if, say, eyes started to develop in these critters, then atrophied away (like our tails) before hatching.

Check out the life history of the Grotto salamander, Typhlotriton spelaeus Stejneger. It�s found in southern Missouri, extreme southeastern Kansas, and adjacent areas in Arkansas and Oklahoma:

From <a href="http://www.amazon.com/exec/obidos/tg/detail/-/1560988282/qid=1034629937/sr=8-1/ref=sr_8_1/102-8875891-1908936?v=glance&n=507846" target="_blank">Petranka, 1998</a>:

Quote:

The grotto salamander is a cave form with atrophied eyes and a white, pinkish white, or light brown dorsum and venter. The eyes of adults appear as small black spots and the eyelids are partially fused (Brandon 1965c, 1970; Mittleman 1950; Smith 1960) � Adults measure 7.5-13.5 cm TL�

Here�s an image of an adult grotto salamander:

Petranka:

Quote:

Larvae collected from caves tend to be noticeably lighter than those from surface streams. Small and intermediate-sized larvae have functional eyes. Fusion of the lids and atrophy of the eyes begin near the end of the larval stage and continue into the adult stage (Brandon 1970; Smith 1960; Stone 1964.

A larval grotto salamander:

Petranka:

Quote:

Although hatchlings are often found within caves, many drift from caves into surface streams. Larvae are often abundant in streams outside caves, and larval drift may be important in dispersing individuals from one cave system to another.

Because the adults are almost always found in caves, some researchers have suggested that larvae migrate from surface streams back into caves shortly before reaching sexual maturity. Brandon (1971b) noted that there is no empirical evidence that surface-dwelling larvae return to caves and surmised that most adults are derived from larvae within caves.
The larvae are secretive and remain in recesses in gravel or underneath large, flat rocks, where they forage for small invertebrates (Smith 1960). Larvae are largely sit-and-wait predators that do not show strong tendencies to search actively for prey. Individuals often posture with the anterior portion of the body raised well above the substrate, a behavior that may enhance prey detection (Dodd 1980). An isopod (Lirceus happinae) is the major prey item of larvae in some populations (Smith 1948a,b). Lirceus probably serves as a secondary host of Ophiotaenia cestodes, a parasite that infects many of the larvae. Brandon (1971b) found only dipteran larvae and snails in larvae.

If surface-dwelling larvae do in fact return to caves, then the fact that some larvae are swept out into streams would act as a selective pressure for retention of functional eyes until metamorphosis, after which the adults stay up on the cave walls. I suppose the creationist would say that this is intelligent design, enabling the stream-dwelling larvae to see, but since many of the larvae stay in the caves until metamorphosis, an intelligent designer should be able to figure out a way to keep them all in the caves and not have to bother with functional eyes at all.

What�s your take on this Vanderzyden?

edited to add an additional image that I found.

[ October 14, 2002: Message edited by: Zetek ]

Dr Rick · 10-14-2002, 03:20 PM

[

Quote:

Originally posted by trientalis:
Does the appendix aid in digestion? I had the impression it was just there to become inflamed and burst at inconvenient moments.
Do tell me more.

The human appendix's sole positve impact is that it sometimes pays a surgeon's mortgage.

It's presence neither aids digestion nor offers any survival advantage. It does create the risk of a festering abscess that may kill it's hapless victim or cause infertility, it is a source of rare, sometimes fatal carcinoid tumors, and it possibly plays a negative role in some immune-related digestive disorders that make ten's of thousand of people miserable everyday.

Rick

trientalis · 10-14-2002, 03:33 PM

Everybody loves a good lap appy, eh?

Thanks all for your interesting answers.

Vanderzyden · 10-14-2002, 03:34 PM

Quote:

Originally posted by Doubting Didymus:
There are two main points involved here, so specifically, I would like to know what are you taking issue with.

Is it: That non-functioning, useless eyes exist? (that is, you acknowledge that eyeless cave dwellers exist, but you do not think that they do, in fact, have useless vestigial eyes).

Or, given that nonfunctional eyes exist, do you not accept that the organism would be improved by removing them.

Neither.

Clearly, the cave fish is eye-less. It does NOT have eyes at all, so it is nonsense to comment on their function. The eyes never developed. Useless eyes are different from not having eyes at all. Yes, the remnants of embryonic eye forms are (apparently) present, but they are non-organs. So, we could hardly call these "useless" eyes.

Despite your later clarification on "selection", it would seem that blindness is an evolutionary regression. Macroevolution, if it is in operation, is a non-person. It would therefore be unable to make value judgments and assessments, or "decide" among the potential benefits of alternatives. But you and I are persons capable of such things. As such, we can see that it is a degradation to move from complex, sophisticated functions to retarded or absent functions.

We may also examine the issue from the ID perspective, and consider the role of a designer who is varying a general specification. From this perspective, it seems quite sensible to avoid or curtail the production of an organ that will not be used. As you suggest, it would be appropriate for the development of an eye to be removed from the specification of the cave-dwelling fish. If this is the case, then the animal does not possess any extraneous organs, and the flexibility of the designer is demonstrated. I wouldn't be surprised to discover that many of the examples of those "sub-optimal" designs are of this nature.

Vanderzyden

[ October 14, 2002: Message edited by: Vanderzyden ]

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10-14-2002, 06:27 AM	#162
Blinn Veteran Member Join Date: Aug 2001 Location: Ohio, USA Posts: 1,162

10-14-2002, 07:37 AM	#164
Nialler Banned Join Date: Dec 2001 Location: Paris Posts: 8,473	I've just trawled through 7 pages which were alternately enlightening and deeply frustrating. Am I the only one to perceive the irony inherent in a discussion about a being which has evolved to a state when it does not need to see, said discussion taking place with its precise human conterpart?

10-14-2002, 03:33 PM	#169
trientalis Senior Member Join Date: Sep 2001 Location: Washington state Posts: 848	Everybody loves a good lap appy, eh? Thanks all for your interesting answers.

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