The Design in Light
That the radiation from
the sun (and from many sequence stars) should be concentrated into
a minuscule band of the electromagnetic spectrum which provides
precisely the radiation required to maintain life on earth is very
Ian Campbell, British Physicist 65
The sun is probably the one thing we see most often throughout
our lives. Whenever we raise our sight to the sky during the day,
we can see its dazzling light. If someone were to come up and ask
"What good is the sun? we would probably reply without even a thought
that the sun gives us light and heat. That answer, although a bit
superficial, would be correct.
But does the sun just "happen" to radiate light and heat
for us? Is it accidental and unplanned? Or is the sun specially
designed for us? Could this great ball of fire in the sky be a gigantic
"lamp" that was created so as to meet our exact needs?
Recent research indicates that the answer to the last
two questions is "yes". "Yes" because in sunlight there is a design
that inspires amazement.
The Right Wavelength
Both light and heat are different
manifestations of electromagnetic radiation. In all its manifestations,
electromagnetic radiation moves through space in waves similar to
those created when a stone is thrown into a lake. And just as the
ripples created by the stone may have different heights and the distances
between them may vary, electromagnetic radiation also has different
The analogy shouldn't be taken too far however because
there are huge differences in the wavelengths of electromagnetic
radiation. Some are several kilometers long while others are shorter
than a billionth of a centimeter and the other wavelengths are to
be found in a smooth, unbroken spectrum everywhere in between. To
make things easier, scientists divide this spectrum up according
to wavelength and they assign different names to different parts
of it. The radiation with the shortest wavelength (one-trillionth
of a centimeter) for example is called "gamma rays": these rays
pack tremendous amounts of energy. The longest wavelengths are called
"radio waves": they can be several kilometers long but carry very
little energy. (One result of this is that radio waves are quite
harmless to us while exposure to gamma rays can be fatal.) Light
is a form of electromagnetic radiation that lies between these two
The first thing to be noticed about the electromagnetic
spectrum is how broad it is: the longest wavelength is 1025
times the size of the shortest one. Written out in full, 1025
looks like this:
A number that big is pretty meaningless by itself. Let's
make a few comparisons.
For example, in 4 billion years (the estimated age of
the earth) there are about 1017 seconds. If you wanted
to count from 1 to 1025 and did so at the rate of one
number a second nonstop, day and night, it would take you 100 million
times longer than the age of the earth! If we were to build a pile
of 1025 playing cards, we would end up with a stack stretching
halfway across the observable universe.
This is the vast spectrum over which the different wavelengths
of the universe's electromagnetic energy extend. Now the curious
thing about this is that the electromagnetic energy radiated by
our sun is restricted to a very, very narrow section of this spectrum.
70% of the sun's radiation has wavelengths between 0.3 and 1.50
microns and within that narrow band there are three types of light:
visible light, near-infrared light, and ultraviolet light.
Three kinds of light might seem quite enough but all
three combined make up an almost insignificant section of the total
spectrum. Remember our 1025 playing cards extending halfway
across the universe? Compared with the total, the width of the band
of light radiated by the sun corresponds to just one of those cards!
Why should sunlight be limited to such a narrow range?
The answer to that question is crucial because the only
radiation that is capable of supporting life on earth is the kind
that has wavelengths falling within this narrow range.
In Energy and the Atmosphere, the British
physicist Ian Campbell addresses this question and says "That the
radiation from the sun (and from many sequence stars) should be
concentrated into a minuscule band of the electromagnetic spectrum
which provides precisely the radiation required to maintain life
on earth is very remarkable." According to Campbell, this situation
Let us now examine this "staggering design of light"
From Ultraviolet to Infrared
We said that there was a range of
1:1025 in the sizes of the longest and shortest electromagnetic
wavelengths. We also said that the amount of energy that was carried
depended upon the wavelength: shorter wavelengths pack more energy
than longer ones. Another difference has to do with how radiation
at different wavelengths interacts with matter.
The shortest forms of radiation are called (in increasing
order of wavelength) "gamma rays", "X-rays", and "ultraviolet light".
They have the ability to split atoms because they are so highly
energized. All three can cause molecules–especially organic molecules–to
break up. In effect, they tear matter apart at the atomic or molecular
Radiation with wavelengths longer than visible light begins at infrared
and extends up to radio waves. Its impact upon matter is less serious
because the energy it conveys is not as great.
The "impact upon matter" that we spoke of has to do with
chemical reactions. A significant number of chemical reactions can
take place only if energy is added to the reaction. The energy required
to start a chemical reaction is called its "energy threshold". If
the energy is less than this threshold, the reaction will never
start and if it is more, it is of no good: in either case, the energy
will have been wasted.
In the whole electromagnetic spectrum, there is just
one little band that has the energy to cross this threshold exactly.
Its wavelengths range between 0.70 microns and 0.40 microns and
if you'd like to see it, you can: just raise your head and look
around–it's called "visible light". This radiation causes chemical
reactions to take place in your eyes and that is why you are able
The radiation known as "visible light"
makes up 41% of sunlight even though it occupies less than 1/1025
of the whole electromagnetic spectrum. In his famous article "Life
and Light", which appeared in Scientific American, the renowned
physicist George Wald considered this matter and wrote "the radiation
that is useful in prompting orderly chemical reactions comprises
the great bulk of that of our sun."67 That the
sun should radiate light so exactly right for life is indeed an
extraordinary example of design.
Nearly all of the sun's radiation
is restricted to a narrow band of wavelengths ranging from
0.3 to 1.50 microns. This band encompasses near ultraviolet,
visible, and infrared light.
Is the rest of the light the sun radiates good for anything?
When we look at this part of the light
we see that a large part of solar radiation falling outside the
range of visible light is in the section of the spectrum called
"near infrared". This begins where visible light ends and again
occupies a very small part of the total spectrum–less than 1/1025.68
Is infrared light good for anything? Yes, but this time
it's no use to look around because you can't see it with the naked
eye. However you can easily feel it: the warmth you feel on your
face when you look up on a bright sunny summer or spring day is
caused by infrared radiation coming from the sun.
The sun's infrared radiation is what carries the thermal
energy that keeps Earth warm. It too is as essential for life as
visible light is. And the fascinating thing is that our sun was
apparently created just to serve for these two purposes, because
these two kinds of light make up the greatest part of sunlight.
And the third part of sunlight? Is that of any benefit?
You can bet on it. This is "near ultraviolet
light" and it makes up the smallest fraction of sunlight. Like all
ultraviolet light, it is highly energized and it can cause damage
to living cells. The sun's ultraviolet light however is the "least
harmful" kind since it is closest to visible light. Although overexposure
to solar ultraviolet light has been shown to cause cancer and cellular
mutations, it has one vital benefit: the ultraviolet light concentrated
in such a miniscule band 69 is needed for the
synthesis of vitamin D in humans and other vertebrates. (Vitamin
D is necessary for the formation and nourishment of bone: without
it, bones become soft or malformed, a disease called rickets that
occurs in people deprived of sunlight for great lengths of time.)
In other words, all the radiation emitted by the sun
is essential to life: none of it is wasted. The amazing thing is
that all this radiation is limited to a 1/1025 interval
of the whole electromagnetic spectrum yet it is sufficient to keep
us warm, see, and allow all the chemical reactions necessary for
life to take place.
Even if all the other conditions necessary for life and
mentioned elsewhere in this book existed, if the light radiated
by the sun fell into any other part of the electromagnetic spectrum,
there could be no life on Earth. It is certainly impossible to explain
the fulfillment of this condition having a probability of 1 in 1025
with a logic of coincidence.
And if all this were not enough, light does something else: it keeps
us fed, too!
Photosynthesis and Light
Photosynthesis is a chemical
process whose name almost everyone who's ever gone to school will
be familiar with. Most people however fail to realize how vitally
important this process is for life on Earth or what a mystery its
First let's brush off our high-school
chemistry and take a look at the formula for the photosynthesis
6H2O + 6CO2
+Sunlight --> C6H12O6
Translated into words this
means: Water and carbon dioxide and sunlight produces glucose and
To be more exact what is happening in this chemical reaction is that
six molecules of water (H2O) combine with six molecules
of carbon dioxide (CO2) in a reaction that is energized
by sunlight. When the reaction is complete, the result is a single
molecule of glucose ( C6H12O6), a
simple sugar that is a fundamental element of nutrition-, and six
molecules of gaseous oxygen (O2). The source of all nutriments
on our planet, glucose contains a great deal of energy.
Simple though this reaction may look, it is in fact incredibly
complex. There is only one place where it occurs: in plants. The
plants of this world produce the basic food for all living things.
Every other living thing is ultimately nourished in one way or another
by glucose. Herbivorous animals eat the plants themselves and carnivorous
animals eat plants and/or other animals. Human beings are no exception:
our energy is derived from the food we eat and comes from the same
source. Every apple, potato, chocolate, or steak or anything else
you eat is supplying you with energy that came from the sun.
But photosynthesis is important for another reason. The
reaction has two products: in addition to glucose, it also releases
six molecules of oxygen. What's happening here is that plants are
continuously cleaning up an atmosphere that is constantly being
"polluted" by air-breathing creatures-human beings and animals,
whose energy is derived from combustion in oxygen, a reaction that
produces carbon dioxide. If plants didn't release oxygen, the oxygen-breathers
would eventually use up all the free oxygen in the atmosphere and
that would be the end of them. Instead, the oxygen in the atmosphere
is constantly being replenished by plants.
Without photosynthesis, plant
life could not exist; and without plant life, there would be no
animal or human life. This marvelous chemical reaction, which
has never been duplicated in any laboratory, is taking place deep
in the grass you step on and in trees you may not even notice.
It once occurred in the vegetables on your dinner plate. It is
one of the fundamental processes of life.
hundreds of millions of years, plants have been busy doing
something no laboratory has ever been able to duplicate:
Using sunlight, the produce food. A crucial condition for
this extraordinary transformation however is that the light
that the plants receive must be precisely right for photosynthesis
to take place.
The interesting thing is what a carefully-designed process
photosynthesis is. When we study it, we can't help but observe that
there is a perfect balance between plant photosynthesis and the
energy consumption of oxygen-breathers. Plants supply glucose and
oxygen. Oxygen-breathers burn the glucose in the oxygen in their
cells to get energy and they release carbon dioxide and water (in
effect, they're reversing the photosynthesis reaction) that the
plants use to make more glucose and oxygen. And so it goes on, a
continuous cycle that is called the "carbon cycle" and it is powered
by the energy of the sun.
In order to see how perfectly-created this cycle truly
is, let us focus our attention on just one of its elements for the
moment: the sunlight.
In the first part of this chapter we looked at sunlight
and found that its radiation components were specially tailored
to allow life on Earth. Could sunlight also be deliberately tailored
for photosynthesis as well? Or are plants flexible enough so that
they can perform the reaction no matter which kind of light reaches
The American astronomer George Greenstein discusses this
in The Symbiotic Universe:
Chlorophyll is the molecule
that accomplishes photosynthesis... The mechanism of photosynthesis
is initiated by the absorption of sunlight by a chlorophyll molecule.
But in order for this to occur, the light must be of the right color.
Light of the wrong color won't do the trick.
THE FITNESS OF SUNLIGHT AND CHLOROPHYLL
Plants are able to perform photosynthesis because the chlorophyll
molecules in their cells are sensitive to sunlight. But chlorophyll
is only able to use a very limited range of light wavelengths
and those are the wavelengths that the sun radiates the most.
What is even more interesting is that this interval corresponds
to just 1/1025 of the whole electromagnetic spectrum.
In the two graphs above, the extraordinary fitness between
sunlight and chlorophyll can be seen. In the upper chart is
the distribution of the light emitted by the sun. In the lower
one is the light under which photosynthesis will work. The
fact that these two curves are almost identical is an indication
of how perfectly designed visible light is.
A good analogy is that of a television set. In
order for the set to receive a given channel it must be tuned to
that channel; tune it differently and the reception will not occur.
It is the same with photosynthesis, the Sun functioning as the transmitter
in the analogy and the chlorophyll molecule as the receiving TV
set. If the molecule and the Sun are not tuned to each other-tuned
in the sense of colour- photosynthesis will not occur. As it turns
out, the sun's color is just right.70
In the last chapter we drew attention to the error inherent
in the idea of the adaptability of life. Some evolutionists hold
that "if conditions had been different, life would have evolved
to be perfectly in harmony with them as well". Thinking superficially
about photosynthesis and plants, one could come to a similar conclusion:
"If sunlight were different, plants would have just evolved according
to that." But this is in fact impossible. Although he's an evolutionist
himself, George Greenstein admits this:
might think that a certain adaptation has been at work here: the
adaptation of plant life to the properties of sunlight. After all,
if the Sun were a different temperature could not some other molecule,
tuned to absorb light of a different colour, take the place of chlorophyll?
Remarkably enough the answer is no, for within broad limits
all molecules absorb light of similar colours. The absorption of
light is accomplished by the excitation of electrons in molecules
to higher energy states, and the same no matter what molecule you
are discussing. Furthermore, light is composed of photons, packets
of energy and photons of the wrong energy simply can not be absorbed…
As things stand in reality, there is a good fit between the physics
of stars and that of molecules. Failing this fit, however, life
would have been impossible.71
What Greenstein is saying
briefly is this: No plant can only perform photosynthesis except within
a very narrow range of light wavelengths. And that range corresponds
exactly to the light given out by the sun.
The harmony between stellar and molecular physics that
Greenstein refers to is a harmony too extraordinary ever to be explained
by chance. There was only one chance in 1025 of the sun's
providing just the right kind of light necessary for us and that
there should be molecules in our world that are capable of using
that light. This perfect harmony is unquestionably proof of intentional,
In other words, there is a single Creator, the Ruler
of starlight and of the molecules of plants Who has created all
these things in harmony with one other, exactly as is revealed in
He is Allah- the Creator, the Maker, the
Giver of Form. To Him belong the Most Beautiful Names. Everything
in the heavens and earth glorifies Him. He is the Almighty, the
All Wise. (Surat al-Hashr: 24)
The Light of Your Eyes
We have seen how the light
coming to us from the sun consists of just three narrow bands of the
1) Infrared light, whose wavelengths are longer than
visible light and which keeps Earth warm.
2) A small amount of ultraviolet light, whose wavelengths
are shorter than visible light and which is necessary for the synthesis
of vitamin D among other things.
3) Visible light, which makes vision possible and supports
The existence of a range of "visible light" is as important
for the support of biological vision as it is for photosynthesis.
The reason is that it is impossible for a biological eye to see
any band of the spectrum outside that of visible light and a very
small section of near infrared.
To explain why this should be so, we
first need to understand how vision takes place. It begins with
particles of light called "photons" passing through the pupil of
eye and falling onto the surface of the retina located at the back
of the eye. The retina contains cells that are light-sensitive.
They are so sensitive that each can recognize when even a single
photon strikes it. The photon's energy activates a complex molecule
called "rhodopsine", large quantities of which are contained in
these cells. The rhodopsine in turn activates other cells and those
activate still others in turn.72 Eventually an
electrical current is generated and this is carried to the brain
by the optic nerves.
The first requirement for this system to work is that
the retina cell must be able to recognize when a photon strikes
it. For that to happen, the photon must carry an exact amount of
energy: if it is too much or too less, it won't activate the formation
of rodopsine. Changing the size of the eye makes no difference:
the crucial thing is the harmony between the size of the cell and
the wavelengths of the photons coming in.
The only rays of light that are suitable for biological
vision have wavelengths that fall within the range of what
is called "visible light". A large part of the energy that
is emitted by the sun falls in that range.
Designing an organic eye that could see other ranges of the electromagnetic
spectrum turns out to be impossible in a world dominated by carbon-based
life. In Nature's Destiny, Michael Denton explains this subject
in detail and confirms that an organic eye can only see within the
range of visible light. While other models of eyes that could, in
theory, be designed, none of them would be able to see different
ranges of the spectrum. Denton tells us why:
X-ray, and gamma rays are too energetic and are highly destructive,
while infrared and radio waves are too weak to be detected because
they impart so little energy interacting with matter... And so it
would appear that for several different reasons, the visual region
of the electromagnetic spectrum is the one region supremely fit
for biological vision and particularly for the high-resolution vertebrate
camera eye of a design and dimension very close to that of
the human eye.73
Pausing to think about everything
that has been said so far, we come to this conclusion: The sun radiates
energy within a narrow band (a band so narrow that it corresponds
to just 1/1025 of the whole electromagnetic spectrum) that
has been carefully chosen. So finely adjusted is this band that it
keeps the world warm, supports the biological functions of complex
life-forms, enables photosynthesis, and allows the creatures of this
world to see.
In "The Blue Planet" we compared
our world with the other planets of the solar system and found that
the range of temperatures necessary for life exists only on Earth.
The biggest reason for this is that the earth is just the right distance
from the sun: the outer planets like Mars, Jupiter, or Pluto are too
cold while the inner planets Venus and Mercury are too hot.
The Right Star, the Right Planet, and the Right Distance
Those who refuse to admit that there
is intentional design in the distance between Earth and Sun suggest
something like the following:
"The universe is full
of stars, some of them much bigger than the sun and some of them
much smaller. These could very well have planetary systems of their
own. If a star is bigger than the sun, then the ideal planet for
life would be located at a much greater distance than the earth
is from the sun. For example, a planet in an orbit around a red
giant at the distance of Pluto could have a temperate climate like
our world has. Such a planet would be just as fit for life as our
The claim is invalid in one
very important respect for it ignores the fact that stars of different
masses radiate different types of energy.
The factors that determine the wavelengths of the energy
that a star radiates are its mass and its surface temperature (the
latter of which is directly related to mass). For example, the sun
radiates near ultraviolet, visible, and near infrared light because
its surface temperature is around 6,000°C. If the sun's mass were
a bit bigger, its surface temperature would be higher; but in that
case, the energy levels of the sun's radiation would also be higher
and the sun would be radiating much more destructive ultraviolet
rays than it does.
This tells us that any star that is to radiate
light that will support life absolutely must have a mass close to
that of our sun. But if there are to be life-supporting planets
orbiting around such stars, those planets must be located at distances
not substantially different from that between the earth and the
In other words, no planet revolving around a red giant,
a blue giant, or any other star whose mass was substantially different
from the sun's could harbor life. The only source of energy capable
of supporting life is a star like our sun. The only planetary distance
that is suitable for life is the distance between the earth and
There is another way of expressing this truth: The sun
and the earth were each created to be just as they needed to be.
And indeed, in the Qur'an it is revealed that Allah created everything
according to precise calculation:
It is He Who splits the sky at dawn, and appoints
the night as a time of stillness and the sun and moon as a means
of reckoning. That is what the Almighty, the All-Knowing has ordained.
(Surat al-Anam: 96)
Since the beginning of this chapter
we have been talking about the radiation given out by the sun and
how it was specially designed to support life. There is yet another
crucially important factor that we have not yet touched upon: In order
for this radiation to reach the earth's surface, it has to pass through
The Harmony of Light and Atmosphere
Sunlight certainly couldn't do us any good if the atmosphere
didn't let it through. But it does; in fact, our atmosphere is specially
designed to be transparent to this beneficial radiation.
The really interesting thing is not so much that the
atmosphere allows beneficial sunlight to pass but that sunlight
is the only radiation that it allows through. The atmosphere lets
in the visible and near infrared light that is necessary for life
but it blocks other forms of radiation that are deadly. This makes
the atmosphere an important filter against the cosmic radiation
that reaches the earth from the sun and from other sources. Denton
has this to say about the matter:
gases themselves absorb electromagnetic radiation immediately on
either side of the visible and near infrared... The only region
of the spectrum allowed to pass through the atmosphere over the
entire range of electromagnetic radiation from radio to gamma rays
is the exceedingly narrow band including the visible and near infrared.
Virtually no gamma, X, ultraviolet, far infrared, and microwave
radiation reaches the surface of the earth.74
It is impossible to ignore
the artfulness of this design. The sun sends only 1/1025
of the whole range of electromagnetic radiation that could be sent,
that happens to be the range that is good only for us, and that is
the radiation that the atmosphere lets through! At this point it's
also worth pointing out that nearly all of the near ultraviolet that
the sun radiates gets trapped by the atmosphere's ozone layer.
Another point that makes this even more interesting is
that, like air, water also has an extremely particular sort of transparency:
the only radiation capable of spreading through water is the range
of visible light. Even near infrared radiation, which penetrates
the atmosphere (and thus provides heat) penetrates only a few millimeters
into water. Because of this, only a few millimeters of the surface
of the world's oceans are heated by radiation from the sun. That
heat is conveyed in stages to lower levels and as a result of this,
below a particular depth, the temperature of the seawater is quite
similar all over the world. This of course creates an environment
quite suitable for life.
Another interesting point concerning water is that the
different colors of visible light are able to travel different distances
in it. Below eighteen meters, for example, red light cannot penetrate
while yellow can reach depths of up to a hundred meters. Blue and
green on the other hand descend to 240 meters. This is an extremely
important design because the light that is particularly crucial
for photosynthesis is the blue and green portion of the spectrum.
Since water allows these colors to penetrate more deeply than the
others, photosynthesizing plants can live up to 240 meters beneath
These are all facts of the utmost importance. No matter
what physical law related to light we examine, we discover that
everything has been exactly arranged so that life can exist. Commenting
on this situation, Encyclopedia Britannica admits how extraordinary
it all is:
the importance of visible sunlight for all aspects of terrestrial
life, one can not help being awed by the dramatically narrow window
in the atmosphere absorption and in the absorption spectrum of water.
Air as well as water allows the passage of only that radiation
that is necessary for us to live. All the harmful and deadly
cosmic radiation coming from distant space is caught in this
Materialist philosophy and
Darwinism, which takes materialism as its source, both claim that
human life appeared in the universe by chance and that it is an "accident"
with no purpose whatsoever. The knowledge that is being gained through
advances in science however is showing that, in every detail of the
universe, there is a design and a plan whose intention is human life.
It is such a design that, even such a component as light, which we
might never have thought about before, is so clearly "just right"
that one can't help but be amazed.
To try and explain such
careful design as "accidental" is irrational. The fact that all
the sun's radiation is constricted to a narrow band just 1/1025
of the total electromagnetic spectrum, the fact that the light
necessary for life falls precisely within that narrow band, the
fact that the atmosphere blocks all other wavelengths of radiation
and admits just these, the fact that water also blocks all other
forms of deadly radiation and permits the passage only of visible
light: Can these really all be coincidences? Such extraordinary
fine-tuning as this can be explained not by chance but only by
conscious design. This in turn shows us that the whole universe
and all the details of that universe–including the light of the
sun that enables us to see and keeps us warm–have been specially
created and arranged for us to live.
Although it blocks all other
forms of radiation, water allows visible light to penetrate
into its depth for many meters. Thanks to this, sea plants
are able to perform photosynthesis. If water did not have
this property, the ecological balance necessary for life
on our planet could not have come into being.
The conclusion reached by science is a truth that has
been taught to mankind in the Qur'an for fourteen centuries. Science
shows that sunlight has been created for us, in other words, that
it has been made to be "at our service". In the Qur'an we are told
that "The sun and moon both run with precision." (Surat ar-Rahman:
5) Elsewhere it is stated:
Allah is He who created the heavens and the
earth and sends down water from the sky and by it brings forth fruits
as provision for you. ...He has made the sun and moon subservient
to you holding steady to their courses, and He has made the night
and day subservient to you. He has given you everything you have
asked Him for. If you tried to number Allah's blessings, you could
never count them. Man is indeed wrongdoing, ungrateful. (Surah Ibrahim:
Ian M. Campbell, Energy and the Atmosphere, London: Wiley, 1977, p.1-2
66. Ian M. Campbell, Energy and the Atmosphere, p.1-2
67. George Wald, "Life and Light", Scientific American,
1959, vol. 201, p.92-108
68. The near infrared range occupies the rays which
extends from 0.70 micron, where visible light ends, to 1.50 micron.
69. This narrow range occupies the ultraviolet rays
between 0.29 micron and 0.32 micron.
70. George Greenstein, The Symbiotic Universe, p
71. George Greenstein, The Symbiotic Universe, p.96-7
72. This chain reaction taking place in the eye is
actually much more complicated. The light reaching the eye passes
through the lens and falls upon the retina in the back. When light
first strikes the retina a photon interacts with a molecule called
11-cis-retinal. The change in the shape of the retinal molecule forces
a change in the shape of the protein, rhodopsin, to which the retinal
is tightly bound. The protein's metamorphosis alters its behaviour.
Now called metarhodopsin II, the protein sticks to another protein,
called transducin. Before bumping into metarhodopsin II, transducin
had tightly bound a small molecule called GDP. But when transducin
interacts with metarhodopsin II, the GDP falls off, and a molecule
called GTP binds to transducin.
Now, two proteins and one chemical molecule are bound to one another
and it is called GTP-transducin-metarhodopsinII. It now binds to a
protein called phosphodiesterase. When attached to metarhodopsin II
and its entourage, the phosphodiesterase acquires the chemical ability
to "cut" a molecule called cGMP. Initially there are a lot of cGMP
molecules in the cell, but the phosphodiesterase lowers its concentration,
just as a pulled plug lowers the water level in a bathtub.
Another protein that binds cGMP is called an ion channel. It acts
as a gateway that regulates the number of sodium ions in the cell.
Normally the ion channel allows sodium ions to flow into the cell,
while a separate protein actively pumps them out again. The dual action
of the ion channel and pump keeps the level of sodium ions in the
cell within a narrow range.
When the amount of cGMP is reduced because of cleavage by the phosphodiesterase,
the ion channel closes, causing the cellular concentration of positively
charged sodium ions to be reduced. This causes an imbalance of charge
across the cell membrane that, finally, causes a current to be transmitted
down the optic nerve to the brain. The result, when interpreted by
the brain, is vision. (Quoted from Michael Behe, Darwin's Black Box,
New York: Free Press, 1996, pp. 18-21).
This is actually a very brief and simplified version of how
we see. If the events developed like this, we would never be able
to see. If the reactions mentioned above were the only ones that operated
in the cell, the supply of 11-cis-retinal, cGMP, and sodium ions would
quickly be depleted. There are many mechanisms that would restore
the cells to their original state.
The reactions described above is far from being a complete biochemical
explanation of seeing and they are only summarized. However, even
what has been related above suggests that seeing is a very complicated
and perfect mechanism which can never come about by evolution.
73. Michael Denton, Nature's Destiny, p 62, 69
74. Michael Denton, Nature's Destiny, p 55
75. Encyclopaedia Britannica, 1994, 15th ed., volume
18, p. 203