THE STORY OF A MOMENT'S COMMUNICATION

Everybody can remember a time when his or her eyes met with an acquaintance's eyes and they greeted one another. Would you believe that this communication of a brief moment has a long story?
Let's assume that on a certain afternoon two men are situated apart from one another. In spite of their close friendship, they have not yet recognised one another. One of these men, turning his head in the direction of his friend, whom he has not yet recognised, starts a chain of biochemical reactions: the light reflected from the body of his friend enters the eye lens at a speed of ten trillion photons (light particles) per second. Light travels through the lens and the fluid that fills the eyeball before falling on the retina. On the retina there are about hundred million cells called "cones" and "rods". Rods differentiate light from dark and cones perceive colours.

CORNEA AND IRIS The cornea, one of the 40 basic components of the eye, is a transparent layer located at the very front of the eye. It allows light through as perfectly as does window glass. It is surely not a coincidence that this tissue, found at nowhere else in the body, is situated just at the right place, that is, the front surface of the eye. Another important component of the eye is the iris, which gives the eye its colour. Located right behind the cornea, it regulates the amount of light admitted into the eye by contracting or expanding the pupil - the circular opening in the middle. In bright light, it immediately contracts. In dim light, it enlarges to allow more light to enter the eye. A similar system has been adapted as a basis for the design of cameras in order to adjust the amount of light intake, but it is nowhere near as successful as the eye.

The human eye functions through the harmonious working of about forty different components. In the absence of even one of these components would make the eye useless. For instance, in the absence of even tear gland alone, the eye would eventually dry out and cease to function. This system, which is irreducible to simplicity, can never be explained by "gradual development" as is claimed by evolutionists. This shows that the eye emerged in a complete and perfect form, which means that it was created.

Depending on the external objects, varying light waves fall on different places on the retina. Let's think about the moment the person in our assumed situation sees his friend. Some features on his friend's face cast different intensities of light on his retina e.g. darker facial features such as eyebrows would reflect light at much lower intensities. Neighbouring cells on the retina, however, receive stronger intensities of light reflected from the forehead of his friend. All of his friend's facial features cast waves of various intensities on the retina of his eye.
What kind of stimuli do these light waves provoke?
The answer to this question is, indeed, very complicated. Nevertheless, the answer has to be examined to fully appreciate the extraordinary design of the eye.

The Chemistry of Seeing

When photons hit the cells of the retina, they activate a chain reaction, rather like a domino effect. The first of these domino pieces is a molecule called "11-cis-retinal" that is sensitive to photons. When struck by a photon, this molecule changes shape, which in turn changes the shape of a protein called "rhodopsin" to which it is tightly bound. Rhodopsin then takes a form that enables it to stick to another resident protein in the cell called "transducin".
Prior to reacting with rhodopsin, tranducin is bound to another molecule called GDP. When it connects with rhodopsin, transducin releases the GDP molecule and is linked to a new molecule called GTP. That is why the complex consisting of the two proteins (rhodopsin and transducin) and a smaller chemical molecule (GTP) is called "GTP-transducinrhodopsin".
The new GTP-transducinrhodopsin complex can now very quickly bind to another protein resident in the cell called "phosphodiesterase". This enables the phosphodiesterase protein to cut yet another molecule resident in the cell, called cGMP. Since this process takes place in the millions of proteins in the cell, the cGMP concentration is suddenly reduced.
How does all this help with sight? The last element of this chain reaction supplies the answer. The fall in the cGMP amount affects the ion channels in the cell. The so-called ion channel is a structure composed of proteins that regulate the number of sodium ions within the cell. Under normal conditions, the ion channel allows sodium ions to flow into the cell, while another molecule disposes of the excess ions to maintain a balance. When the number of cGMP molecules falls, so does the number of sodium ions. This leads to an imbalance of charge across the membrane, which stimulates the nerve cells connected to these cells, forming what we refer to as an "electrical impulse". Nerves carry the impulses to the brain and "seeing" happens there.
In brief, a single photon hits a single cell and, through a series of chain reactions, the cell produces an electrical impulse. This stimulus is modulated by the energy of the photon, that is, the brightness of light. Another fascinating fact is that all of the processes described so far happen in no more than one thousandth of a second. Other specialised proteins within the cells convert elements such as 11-cis-retinal, rhodopsin and transducin back to their original states. The eye is under a constant shower of photons, and the chain reactions within the eye's sensitive cells enable it to percieve each one of these photons.32

The first step in seeing is a small change created by light in the structure of a minute molecule called 11-cis-retinal that causes a change in a larger protein called rhodopsin to which it is attached.

The process of sight is actually a great deal more complicated than the outline presented here would indicate. However, even this brief overview is sufficient to demonstrate the extraordinary nature of the system. There is such a complicated, finely calculated design inside the eye that chemical reactions in the eye resemble the domino shows in the Guinness Book of World Records. In these shows, tens of thousands of domino pieces are so strategically placed that tipping the first piece activates the entire system. In some areas of the domino chain, many apparatuses are installed to start a new sequences of reactions, e.g. a winch carrying a piece to another location and dropping it exactly at the place necessary for a further sequence of reactions.
Of course, nobody thinks that these pieces have been "coincidentally" brought to their precise locations by winds, quakes or floods. It is obvious to everyone that each piece has been placed with great attention and precision. The chain reaction in the human eye reminds us that it is nonsense to even entertain the thought of the word "coincidence". The system is composed of a number of different pieces assembled together in very delicate balances and is a clear sign of "design". The eye is created flawlessly.

Click image to see larger photo The figure above illustrates the biochemistry of vision. Symbols indicate; RH=Rhodopsin, Rhk=Rhodopsin Kinase, A=Ariestin, GC=Guanylate Cyclase, T=Tranducin, PDE=Phosphodiesterase.

Biochemist Michael Behe comments on the chemistry of the eye and the theory of evolution in his book Darwin's Black Box:
Now that the black box of vision has been opened, it is no longer enough for an evolutionary explanation of that power to consider only the anatomical structures of whole eyes, as Darwin did in the nineteenth century (and as popularizers of evolution continue to do today). Each of the anatomical steps and structures that Darwin thought were so simple actually involves staggeringly complicated biochemical processes that can not be papered over with rhetoric.33

Beyond Seeing

What has been explained so far is the first contact of photons, reflected off a friend's body, with a man's eye. The retinal cells produce electrical signals through complicated chemical processes as described above. In these signals there exists such detail that the face of the man's friend in the example, his body, hair colour and even a minute mark on his face have been encoded. Now the signal has to be carried to the brain.
Nerve cells (neurons) stimulated by retinal molecules show a chemical reaction as well. When a neuron is stimulated, protein molecules on its surface change shape. This blocks the movement of the positively charged sodium atoms. The change in the movement of the electrically charged atoms creates a voltage differential within the cell, which results in an electrical signal. The signal arrives at the tip of the nerve cell after travelling a distance shorter than a centimetre. However, there is a gap between two nerve cells and the electrical signal has to cross this gap, which presents a problem. Certain special chemicals between the two neurons carry the signal. The message is carried this way for about a quarter to a fortieth of a millimetre. The electrical impulse is conducted from one nerve cell to the next until it reaches the brain.
These special signals are taken to the visual cortex in the brain. The visual cortex is composed of many regions, one on top of the other, about 1/10 inch (2.5 mm) in thickness and 145 square feet (13.5 square metres) in area. Each one of these regions includes about seventeen million neurons. The 4th region receives the incoming signal first. After a preliminary analysis, it forwards the data to neurons in other regions. In any phase, any neuron can receive a signal from any other neuron.
This way, the man's picture forms in the visual cortex of the brain. However, the image now needs to be compared to the memory cells, which is also done very smoothly. Not a single detail is overlooked. Furthermore, if the friend's perceived face looks slightly more pale than normal then the brain activates the thought, "why is my friend's face so pale today?"