Evolution of the Eye

[Moontanman]

Originally Posted by Thunderbird

Ok, I thought you were talking about the one that eat Greeks.
Got any pictures? Are they like hydras?

Google Image Result for http://www.scientificillustrator.com/art/microscopic/cyclops.jpg

[freeztar]

Originally Posted by Moontanman

Google Image Result for http://www.scientificillustrator.com/art/microscopic/cyclops.jpg

Very interesting!

It's interesting to note that it still displays morphological bilateral symmetry.

Are there other examples of "uniphotos"?

[Thunderbird]

I like their shape, would make a good subject for a gem sculpture. Tiger eye or maybe jade.

[Moontanman]

Originally Posted by Thunderbird

I like their shape, would make a good subject for a gem sculpture. Tiger eye or maybe jade.

Lots of vernal pool shrimp are interstingly shaped. Clam shrimp, seed shrimp, tadpole shrimp and fairy shrimp.

[jab2]

The evolution of the eye, or rather spontaneous appearance as they want to argue, is one of the classic examples non-believers in evolution uses to "show" why evolution is a lie. It is thus with great interest that I try and follow all discussions pertaining to it.

The whole development from photo sensitive cells on a flat surface through all the different stages is always very well explained. There is however always the nagging question as to why cells needed to be sensitive to light in the first place and this is never not very well answered.

The following is pure speculation on my part, as I have never came across a proper explanation of why there were a need for photo sensitive cells on the outside of an organism.

If one look at chemistry, virtually all chemical reactions work better or faster when heated. As the molecular workings of any organism is pure chemistry, one can argue that gaining heat from the environment must have been beneficial for an organism, or at least the proto-cold blooded ones. This ability to find hotter environments would definitely favour organisms which were slightly sensitive to heat. But heat is "light" in the infra-red region of the spectrum, and heat and light as supplied by the sun are "cousins". They are both present at the same time, so organisms need not only favour the mutations that had heat sensitive outer covers to find heat, but mutations with a light sensitive skin will also have the ability to find heat. It is thus very easy to envision an evolutionary benefit for light sensitivity on the outside of an organism.

At danger of stealing LJP07's light, I mean thread, I would like to hear your comments on this argument. I would also appreciate pointers to resources on this issue, as I am sure I am not the first to argue this path of development.

[LJP07]

With respect Jab2, that's the primary point I was trying to ask, why is there a need for photosensitive cells and why do they occur in what seems to be randomness in terms of position and no satisfactory explanation as to why the photosensitive cells formed in the very initial first place with just a layer of skin.

[Moontanman]

Originally Posted by LJP07

With respect Jab2, that's the primary point I was trying to ask, why is there a need for photosensitive cells and why do they occur in what seems to be randomness in terms of position and no satisfactory explanation as to why the photosensitive cells formed in the very initial first place with just a layer of skin.

I think I answered this once but just in case, a limited area a of photo sensitivity allows an animal (bacterium or protozoa) to be able to figure out where the light is coming from. Just knowing it's light might be good enough for some bacteria but an animal who needs to follow the light for some reason needs to be able to know which direction the light is coming from. larger more complex animals have the same needs so most really primitive eyes are just light detectors that allow the animals to know where the light is coming from. If the entire animal was equally sensitive to light it wouldn't know where the light is coming from. Cells in a limited area allow the animal to not only know where the light is coming from it allows the animal to orient it's self to the light. the more specialized this area becomes the better the animal can follow the light. later light can be used as a passive way to find out about the environment, avoiding shadows to avoid predators, that sort of thing.

[LJP07]

I understood all of that anyway Moonman...the question is how can say a sheet of perfectly normal skin...just say you had a sheet of skin 20cm x 20cm and each area of that sheet is exposed to the same degree of light, what determines HOW those cells evolve into photosensitive cells and at the SAME time, what governs its location on the sheet assuming the sheet is similar to say the face.

[jab2]

LJP07, I get the impression that you think the path of evolution is navigated by purpose. That is not really so.

Nature does not see a need for something and THEN the organism develop a solution for that need. The changes that is happening by faulty DNA (and other means) are just sorted into beneficial one and non-beneficial ones. The changes that limits the organism more than the unchanged one will loose out in population growth and cease to exist. Likewise a change that will enable the organism to function better than the unchanged ones will overrun the inefficient older type.

It it thus not a question of why there were light sensitive cells. That cells developed by chance. It is the usefulness of these cells to the organism in determining heat and light that pushed it on the path of becoming something as intricate as the eye.

[Thunderbird]

Originally Posted by jab2

LJP07, I get the impression that you think the path of evolution is navigated by purpose. That is not really so.

Nature does not see a need for something and THEN the organism develop a solution for that need. The changes that is happening by faulty DNA (and other means) are just sorted into beneficial one and non-beneficial ones. The changes that limits the organism more than the unchanged one will loose out in population growth and cease to exist. Likewise a change that will enable the organism to function better than the unchanged ones will overrun the inefficient older type.

It it thus not a question of why there were light sensitive cells. That cells developed by chance. It is the usefulness of these cells to the organism in determining heat and light that pushed it on the path of becoming something as intricate as the eye.

To say the evolution of the eye is just accidental is not really going to cut ether. There is more to it than, God did it. Or its just a series of fortuitous mistakes.