Eyes and other advanced structures.

[Psycho]

In evolution, things happen because of mutations in the dna and therefore some feature is created that means that the new organism has an advantage over other, however what i don't understand is that with a complex structure like the eye how would it form, as surely it would take mutiple mutations of the genetic code and just one of them would be useless to the organism and would actually make it worse off therefore meaning it would be at a disadvantage over others of the same speices.

 

This would mean that the animal is killed more easily and won't pass on that information to the next speicies so a structure like the eye would never get a chance to develop.

 

Can anyone explain how it could happen due to evolution?

 

Even a surface that can detect light would be a giant leap from any other surface, so i don't really understand how that could be the answer.

[the tree]

Plenty of things detect light. Practically every plant has a growth hormone that doesn't work as well in the light, so that the plant bends toward the light source, this is part of phototropism, that makes plants so much more complicated than they are given credit for.

 

The grub carpocapsa saltitans (a particularly ugly moth) are known for thier aversion to heat and thier reflexive response to it. They are what makes jumping beans do thier jumping.

 

It's not that great a leap between grubs noticing subtle changes in heat and the simple ocelli that snails use.

[Cap'n Refsmmat]

http://talkorigins.org/indexcc/CB/CB301.html

[Edtharan]

what i don't understand is that with a complex structure like the eye how would it form, as surely it would take mutiple mutations of the genetic code and just one of them would be useless to the organism and would actually make it worse off therefore meaning it would be at a disadvantage over others of the same speices.

The Eye is an amazing and complex structure. It can seem that it could not possible evolve. But it can.

 

Some chemicals involved in biology react to light, some more so than others. Many of these chamicals have other functions than just reacting to light. SOme of these reactions results in a chemical or electircal cascade.

 

If this occured in a nerve (like) cell, this would then be able to be picked up by other nerves and so pass the signal along. This woulld be a big advantage to a createure. Having cells that could determine if they were in light or shadow would allow a create to detect if it was night or day, or if another creature was near them. Please note at this stage there is no eye, just patches of the organisms that can detect if their cells are in light or dark.

 

Any improvemnts to this setup would be an advantage. If a creature, instead of having these patches distributed around the body, had them in regual places, this would enable it to direct this vision and so operate much better.

 

Improvements of this would be good too. Maybe layers of cells from over it to provide protection. If the cells became clear it would also be better.

 

Once you have layers of cells over the eye patches, then you can have them form structures that would eb benificial (like a lense). These first lenses would most likely be something thathelped concentrate light rather than focusing the light, but the better the focus the more advantagious it would be to the organism.

 

Once it "Lense" is able to focus light effectively, we have what most people would recognise as an eye.

 

So by simple steps, and each step provides an advantage to the organisms, eyes can evolve. I have heard of an experiment where they simulated this process on a computer, each step they allowed the computer to produce multiple, biologically possible, changes to the structure. They when from cells that chemically responded to light right up to a human looking eye. On the computer this took around 1,000,000 generations.

 

In the real worlld, this would have taken longer, but it is therefore plauseable that the eye could have easily evolved in organisms (and could even have evolved multiple times and probably has).

[Dak]

surely it would take mutiple mutations of the genetic code and just one of them would be useless to the organism and would actually make it worse off therefore meaning it would be at a disadvantage over others of the same speices.

 

This would mean that the animal is killed more easily and won't pass on that information to the next speicies so a structure like the eye would never get a chance to develop.

 

'just one' of the mutations need not be useless. simple as that.

[Mokele]

 

Above is an image (which I'd *love* the proper reference for, if anyone knows) depicting the various eyes seen in polychaete worms. Since not all organisms need very good eyesight, it's reasonable to expect that eyes have been evolved and lost many times, and that we should also see intermediate stages of the evolution of eyes preserved in some species who simply never needed anything better (in other words, the energetic cost of maintaining more complex eyes wasn't worth the benefits). From left to right, top to bottom, we see a simple pit of photoreceptors (which can tell what direction light comes from), a pinhole camera eye (which can form a crude image), an eye with a vitreous mass (to allow more precise image formation), an eye with a more rounded vitreous mass (even sharper images), and finally an eye with a lens.

 

Mokele

[Skye]

I posted that image a while ago, I got it from some old lecture notes. It didn't have a reference.

[Mokele]

I knew it was from someone here, thanks. Pity it didn't have a reference, though.

[FractalFiend]

Mokele, this should do for you.

 

http://www.stephenjaygould.org/ctrl/futuyma_complex.html