Thread: A Question for Evolution

Exactly why is it that earthworms have no eyes? It makes no difference if it did have eyes, as in the dark, there is no advantage to the blind or the seeing earthworm. Eyes would not affect the chances of survival of the earthworm, so it is basically insignificant in natural selection.

Assuming that earthworms once had eyes, exactly how and why did evolution get rid of the eyes?

There is no record of oligochaeta ever having eyes, for one.

So, since they never had eyes and presumably never had pressure to select eyes, or pressure to select precursors for eyes or even probably living in environments favoring eyes, why would they actually spend energy on eyes or eye precursors to begin with?

besides, it may actually be a disadvantage to have eyes when digging though soil
how long do you think your eyes would last if someone continually rubbed grit in them ? unless there's any reason at all to retain eyes in a subterranean environment, they will be more of a hindrance than an asset

also, the development of any structure takes resources away from the development of other structures, and the tendency is for unused structures to disappear over time (e.g. the eyes of fish living in caves)

Thank you for your answers. It's cleared up my question. :-D

Originally Posted by Liongold

Exactly why is it that earthworms have no eyes? It makes no difference if it did have eyes, as in the dark, there is no advantage to the blind or the seeing earthworm. Eyes would not affect the chances of survival of the earthworm, so it is basically insignificant in natural selection.

Assuming that earthworms once had eyes, exactly how and why did evolution get rid of the eyes?

They don't need them. They have a basic, primitive "brain" whose human equivalent is the limbic system. In humans there are two seperate sight systems..the "what" and "how" pathways. The old pathway ("how") keeps up from blindly walking into walls by alerting us to our surroundings. Information travels from the optic nerve to the superior colliculus in this system. It tells us something is there but we can't quite define it. Worms probably share a similar how system.

This is quite new to me. What is the technical term for these two aspects of our visual perception system? I should like to google for more information.

An interesting demonstration of these two pathways are people with blindsight; consciously they are not aware of seeing anything, yet they can significantly above chance describe the location, color, shape, and movement of objects in front of them. Their eyes see, but their primary visual cortex, which consciously processes sight, is damaged. As John Galt says, this is probably how many animals with less complicated visual systems see.

Originally Posted by paralith

As John Galt says, this is probably how many animals with less complicated visual systems see.

It was gottspeiller who said that. I'm the one asking for the technical term for the two systems.

Originally Posted by John Galt

This is quite new to me. What is the technical term for these two aspects of our visual perception system? I should like to google for more information.

Pick up a copy of The Phantom Brain by V.S. Ramachandran.

Things arent really divided up as simply as that.

There are many unconscious processes from visual inputs which are processed in the brain including say pupillary reflexes and tectospinal reflexes which are not under voluntary control.
Some areas of the brain e.g. the temporal lobe deals with interpreting colour and movement and complex image interpretations.
However the primary visual cortex is the occipital lobe which is where we consciously "see" although there is a lot more processing of this information than we are generally aware of or take for granted.