Evolution of the eye (science, Article, Greek)

[painted wolf]

I'm sorry I don't understand what you are saying here...

You have looked at the demonstrated changes in form for visual systems in animals and you don't see how they are linked?

I'm always fuzzy on what this mythical "in-between" system is that is often held in such high regard by anti-evolutionists. Are you suggesting that some sort of 'half-eye' would ever exist?

Each step of the way the 'eye' remains fully functional for the creature that has it.
The beauty of the 'eye' is that it evolved once and was so successful that it has been in adapted by nearly every major group of multicellular life since. All using the same basic set of genes with subtle mutations. The joy of opsin.

[rocketman]

Originally Posted by painted wolf

The joy of opsin.

Opsin is just the beginning. The number of genes involved in the overall system is huge. And it's the mathematical properties of speculated 'in-between' lenses that bother me, not the ones that have been found. I have no problem with other peoples inferences, unless they expect me to share them.

[painted wolf]

What a handful of Pax genes?
Thats so hard to mathematically justify?

what is an "in-between" lens anyway?

wa:do

[rocketman]

Originally Posted by painted wolf

What a handful of Pax genes?

No. The photosensitive cells are just the beginning. The entire optical system is way more than a handful of genes.

Originally Posted by painted wolf

what is an "in-between" lens anyway?

One that's hard to mathematically justify. But then I already said that.

[painted wolf]

photosensitive cells = opsin + Pax for location and timing.
Out of around 30,000 or so (may be as few as 20,000) genes, a few dozen are a handful.
I'm not seeing the trouble.

One that's hard to mathematically justify. But then I already said that.

so you've set the definition of "in-between" to be impossible to realize.
No wonder you've never seen one.


wa:do

[rocketman]

Originally Posted by painted wolf

photosensitive cells = opsin + Pax for location and timing. Out of around 30,000 or so (may be as few as 20,000) genes, a few dozen are a handful. I'm not seeing the trouble.

Vertebrate eyes for example form from quite a diverse source of embryonic elements through a complex set of events. The neural retina is derived from the diencephalon and is really part of the brain, the lenses come from the surface ectoderm, while the iris and ciliary body arise mostly (not totally) from the neural crest. We know that mice for example require genes from every chromosome for their eyes to work, and that's not even getting into the peripheral but necessary supporting systems. There is an awful lot of genes involved in being able to see. The full range of which is presently unknown.

Pax-6 is not the only master gene that can organise eyeforms, and Pax organises other things as well. It's not as simple as some say. Currently there is some mystery surrounding the reasons why so many different tissue types form the basis of lenses and retinas throughout the phyla. It has been said that understanding what makes eyes different is probably going to be a harder task than finding what they have in common.

Originally Posted by painted wolf

so you've set the definition of "in-between" to be impossible to realize. No wonder you've never seen one.

The basic laws of physics and properties of light that govern lens usefullness are immovable constraints, yet somehow this usefullness has been arrived at via many different pathways. This I find highly doubtful, for no matter how many examples we have of different eye types, we cannot escape the fact that for one to become another it must pass through intermediary stages, which as far as I can tell, a large proportion of said same would not fall into the very narrow band of usefullness.

Eye evolution expert Russell Fernald (who I'm sure does not share my doubts) says: "Also, it is likely that having evolved one eye type, conversion to another type requires intermediate stages that are much worse or useless compared with the existing design. This would make a switch essentially lethal to animals that depend on sight." Which means that once started down a certain eye-type path it seems reasonable to suggest that things could not deviate much from that path.

As I've said earlier, I'm not saying it didn't happen, just that I find it hard to believe.

[painted wolf]

Vertebrate eyes for example form from quite a diverse source of embryonic elements through a complex set of events.

diverse source but only a few genes... Vertebrates for instance have only four Hedgehog genes, dispite how important they are.
Makes the whole evolution thing much easier.

The basic laws of physics and properties of light that govern lens usefullness are immovable constraints, yet somehow this usefullness has been arrived at via many different pathways. This I find highly doubtful, for no matter how many examples we have of different eye types, we cannot escape the fact that for one to become another it must pass through intermediary stages, which as far as I can tell, a large proportion of said same would not fall into the very narrow band of usefullness.

Actually the lens only arrived via two pathways. One for Cephalopods and one for the rest of us.
Not that big of a problem as you would make it seem.

As for narrow bands of usefullness... our eyes are pathetic in comparison to many out there. Heck even chickens have better eyes than us. Doesn't stop us from makeing the most of our narrow band of usefullness does it?
You have dispite your objections, a very mistaken (and typically creationist) notion of "intermediate stages".

as for your quote mine, the rest will help:
"Although this argument makes sense intuitively, some existing cases of novel optical combinations suggest this is probably not the whole story."

you should try reading the rest of the article it may clear up your confusion.
Karger Gazette No 64 > The Evolution of Eyes

wa:do

[rocketman]

Originally Posted by painted wolf

diverse source but only a few genes...

You forgot all of the changes to muscles, bones, nerves, brain, programming etc etc. If Fernald says the full range is presently unkown then that's good enough for me. You did read his article?

Originally Posted by painted wolf

Not that big of a problem as you would make it seem.

But there are many applications. You don't understand.

Originally Posted by painted wolf

as for your quote mine, the rest will help:

Perhaps it seems like a quote mine to you because you missed my point, which was that the concept of difficult intermediate stages was not something I made up. Speaking of quote mining, don't forget to mention that I said that I'm sure he wouldn't share my doubts.

Originally Posted by painted wolf

you should try reading the rest of the article it may clear up your confusion.

I have no confusion. It all seems very doubtful to me. Of that I'm sure.

[painted wolf]

You forgot all of the changes to muscles, bones, nerves, brain, programming etc etc.

you forget the effect a single mutation on a single gene can have on the whole organism.
ONE MUTATION OF A HEDGEHOG GENE

if a single mutation can totoaly rewrite the skull, muscle, tissue, nervous and brain of this kitten then your agrument is moot. And it did. This is a well known mutation of the Sonic Hedgehog gene, just the one.

Single mutation of the Sonic Hegehog gene. As you can see it effects bone, tissue, vasular, nervous and so on. No need for multiple mutations, one will do just fine.

One mutation, cascade effects. The joys of genes. The biggest problem for creationsits.

wa:do

[rocketman]

Originally Posted by painted wolf

As you can see it effects bone, tissue, vasular, nervous and so on. No need for multiple mutations, one will do just fine.

You don't seem to understand that control genes have to have something to control. There are a great many finely adapted nuances which are being controlled in a 'dumb' way by the control genes in your example. Let's not suggest that a single control gene change brought about vision.