evolution-chicken or egg type of question - (Dec/15/2010 )

I've seen pictures of eyeless, cave dwelling fish. Did these fish start out eyeless and find safety in caves where their predators couldn't see them or did they lose their eyes throughout generations of living in the dark ? If they lost their eyes over time, why didn't they just keep their eyes and not use them. How would being eyeless be an adaptation ? Less eye infections ? More room for other sensory organs ?

Started wondering about this last night when I saw a video of a blue shark eating krill. I got to wondering if basking and whale sharks might have evolved from fish or seal or ... eating carnivores that took up eating krill because they needed to, eventually evolving into filter feeders. If so, I wondered why they didn't still have big teeth. I also wondered if those filter feeders might have been filter feeders all along.

It's probably obvious I'm not a scientist, so please don't be harsh on me if I said things that are dumb.

lwfg on Wed Dec 15 18:37:04 2010 said:

Because in evolution you don't make any choices what to "keep" and what to "lose" - it's all only the matter of natural selection, mutations, genetic drift etc.

When you have eyes and use them, any mutation that would damage your eyesight is not beneficial, lowers your chances to find food, to procreate, to hide from predators. If you don't use them - mutations won't have a negative effect on your survival (or even may have positive because lack of organ means not need to spend energy to grow it leaving your body more for other activities) and after generations you may find a species without eyesight or eyes at all.

lwfg on Wed Dec 15 18:37:04 2010 said:

Sharks did not evolve from "fish" - they are "fish". And seal is a mammal - waaay long from sharks in evolution...

and the surprising thing is that you need just a detrimental mutation in one control gene to stop the development of eyes: PAX6

Thank you Hobgoblin,

You seem to agree with the possibility of cave dwelling fish losing eyes might be beneficial,eg., by leaving room for other sensory organs to develop, or by your idea, saving energy.

Sorry my question about the sharks wasn't worded well, what I meant to say was "fish or seal or (?) EATING carnivores", ie., sharks that ate fish or seals.

Do you think filter feeding sharks:
1. started out as filter feeders, or
2. evolved from carnivores that ate fish or seals or (?), or
3. something different ?

If they didn't start out as filter feeders, maybe a mutation shark was born with teeth that were too small to eat large prey, but was still able to thrive on smaller prey like krill so it was able to pass its little teeth trait around. It's occurring to me that there are large fish that
feed on large prey but have no teeth though.
Maybe they never were large prey eaters but filter fed early on and evolved huge because it was advantageous to be able to filter through a huge amount of water per day.

Please let me know what you think. Thank you very much.

I'm not a shark expert, but have a read here. It's quite a nice read and they support the 2. point. I.e. they evolved from carnivorous species and made a specialisation due to favourable environmental conditions (i.e. spread of plankton).

Thank you for that. I hope to read it tonight.

Yes, because "SOME INTELLIGENCE (and we're not saying it's a god even though we really think that) DID IT!!!" is not an answer.

Wasnt there an article published a few weeks ago stating for once and for ever that the X came before the Y (cant remember if it was the egg of the chicken, I think it was the chicken).
They were able to prove it.. but I only glanced at the article since I was in a rush and forgot to ask a copy
Anyone read it perhaps?