What YE creationists like to quote from Darwin:
To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree.
What YE creationists remove from that quote, to make it appear that Darwin thought eyes could not evolve:
Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real. How a nerve comes to be sensitive to light, hardly concerns us more than how life itself first originated; but I may remark that several facts make me suspect that any sensitive nerve may be rendered sensitive to light, and likewise to those coarser vibrations of the air which produce sound.
(Darwin 1872, 143-144)
This long quotation from Darwin does nothing to touch the real problem which nether you nor he recognise.
It does, however, demonstrate the dishonesty of many YE creationists.
The problem does not lie in the complexity or otherwise of the organ. It lies in the fact the the organism is able to see at all.
So it's an imaginary problem, then? After all, you can sense light with nothing more than your bare skin. No brain required. (radiation can be sensed and acted upon by the spinal cord)
As we all know, or should, anyway, the eye does not do the seeing. It receives light and the messages transmitted to the central processing unit in the organism, wherever that might be, is interpreted there.
For some highly evolved eyes, yes. But there are much simpler forms, for which no optic tectum is required at all. Indeed, organisms without brains can detect light and act on that information.
How did that unit arise, is the problem which neither you, Darwin nor anybody else has ever been able to account for.
Comparative neurology of the optic tectum in ray-finned fishes: patterns of lamination formed by retinotectal projections.
C S Von Bartheld, D L Meyer in Brain Research (1987)
Surprise.
How did the ability to interpret that information arise?
In plants, for example, it was the differential degradation of auxins by sunlight on the light and dark sides of the plant.
Electronic pulses are transmitted by wire or through the air, and are first received, then decoded, then changed into a picture which is then interpreted by ourselves.
What about organisms without brains that do it? I don't think you've given this adequate thought.
But you note the number of stages which must be passed through. Not one of them is simple.
Well, let's take a look...
If an amoebe is going to respond negatively to let's say, a light stimulus,
They do:
Amoeba has no special sense organs. Changes in the outside world are detected by all parts of the living material. In general, this sensitivity ensures favorable surroundings. For instance, amoeba quickly moves away from very bright light or strongly acidic or alkaline water.
http://www.daviddarling.info/encyclopedia/A/amoeba.html
then:
It must have
1 a receptor organ
Nope. No organs.
a transmitting organ which gets the message to
3 a central processing unit which processes the data
4 and interprets it, then
5 an executive unit of some kind which generates the action the organism will take.
Nope. Just one cell. Surprise.
The higher up the scale we go, the more complex the organs involved become. Darwin can argue till the cows come home about the evolution of the receptor organ(s), but has completely fsiled to address the real question of how did vision itself evolve, and from what?
Starting with a mere darkened patch (absorbs more energy and therefore is more sensitive than other parts of the organism), the organism can detect light and detect from which side the light appears.
Useful information.
If the patch is slightly depressed, it increases the acuity of the "eye", because it becomes better able to identify from where the light is coming. Again, a useful thing.
If it becomes more depressed, and the opening narrows, an image can be formed. This is the state of the infrared "eyes" in snakes, which in some of them, can actually be observed to form an image in the optic tectum. Very useful information. Permits a form of night vision. ("small" + "warm" + "moving" = meal)
A clear covered pit protects the sensitive spot, and makes it more durable. If the cover thickens, it also permits focusing for an image.
And so on. Very simple changes, if done one at a time. These stages actually exist in the living members of some phyla. Want to see?
Piece of cake. But the point, of course, was the blatant dishonesty of those who edited Darwin's statement to make it appear he though something he did not.
I don't think that was you. I think you were completely surprised to learn the truth. But you should be more cautious about believing those guys again, um?
