Happy Wonderer

One thing that you have to be careful of is implying that the loss of eye function has to provide any evolutionary benefit to the organism, or that it has to be paired with something else that provides a benefit. All that has to happen is for selective pressure that normally weeds out nonfunctional eyes to be removed.

It is very simple, really. Any zygote with one of the large number of possible genetic errors that cause blindness will likely be removed from the surface population. Not because it starves, but because it is less able to sense predators than its peers.

As the fish move (are forced?) into the caves, the rules change. Blind offspring are not at a disadvantage, but fish who are less able to use other senses are at an advantage. Blindness has been transformed from a 'fatal' mutation to a 'neutral' one. Possibly other mutations that were neutral now become fatal (a non-olefactory fish might survive on the surface because it can use vision to escape predators and locate food.)

In this new environment, the population of blind fish increases because there are a great many more ways of being a blind fish than there are of being a sighted one. (There are an infinite number of possible programs that incorrectly compute the value of pi.)

Blindness doesn't have to happen at greater frequency than other errors in order to get a population of blind fish. There are also a great number of ways to be a fish with a defective heart valve, but those fish are less likely to make it to the age of reproduction.

HW

Albion

No, I know it doesn't have to be associated with a beneficial change. The thing is that Vanderzyden seemed to be wanting to know why fish can't develop traits that would benefit them in a new environment while keeping all the ones they already had. I didn't think that was possible beyond a fairly narrow range, simply because there's a finite number of genes to work with. It's something an intelligent designer might well come up with, because an intelligent designer might be planning for a future where the fish come back out into the light, but evolutionary processes don't account for possible future events.

Oolon Colluphid

I’m not exactly up on fish anatomy (or any, come to that ), but the word you’re after is probably ‘orbit’.

Another interesting thought, one that I suspect hasn’t been investigated: I wonder about these creatures’ brain anatomy. Do they have (probably reduced) brain parts normally asscociated with vision (ie interpretation of signals from eyes)?

Oolon

Vorkosigan

It's more than that. It's because capabilities have costs. Why don't fish talk? Well, they'd need more advanced brains, bigger blood supply, better brain protection, etc.

A fish is a finite object, and so is a fish brain. Making it bigger to handle advanced capabilities has a cost in higher energy demand or demand for processing capacity in the brain. By the same token, a sightless fish has cognitive resources that may, over time, be able to be committed to some other function (smelling, sociality, poker calculations).

Blinn

Apparently gradations of eye reduction exist among individual Mexican blind cave fish. From <a href="http://www.devbio.com/chap06/link0607.shtml" target="_blank">here</a>:

Creation's Terrier

Not exactly impressive. Not only is this still a fish ( ), it's still the same species of fish!

If that much variability is available within kinds, why do we need anything more than microevolution (which creationists accept) to explain what we find in nature?

CT

Blinn

Exactly.

Quetzal

Hey, I agree with CT - all fish merely represent microevolution within the fish kind. Although I do have a question about sharks, etc. Are they fish kind or something else? They don't have swim bladders, after all.

Coragyps

Sharks obviously lost their swim bladders as a result of The Fall: "No legs for you snakes, and hey, sharks, KEEP PADDLING!"

Duvenoy

Hmm. Some nine species of pretty spectacular bacteria, if I remember right.

Some months ago, I did my best to start a fight on a herp forum. I suggested and defended the position that Komodo Monitors were venomous due to the fact that these bacteria were living virtually in symbiosis with the lizard. Therefore, as they often killed it's prey, the saliva should be considered a venom.

We had a fine scrap with great arguments.
It was fun.

The Komodo Monitor is one hell of a sloppy way to build a venomous reptile.

doov