The other half of my friends argument taken from Behe's book regarding the immense complexities of the human eye.
Section taken from Michael J. Behe
's book Darwin Black Box:
But let's touch on the subject of Darwin's theory of how complex eyes evolved:
In the 19th century, the anatomy of the eye was known in detail. The
pupil of the eye, scientists knew, acts as a shutter to let in enough
light to see in either brilliant sunlight or nighttime darkness. The
lens of eye gathers light and focuses it on the retina to form a sharp
image. The muscles of the eye allow it to move quickly. Different
colors of light, with different wavelengths, would cause a blurred
image, except that the lens of the eye changes density over it's
surface to correct for chromatic aberration. These sophisticated
methods astounded everyone who was familiar with them.
Scientists of the 29th century knew that if a person lacked any of the
eyes main integrated features, the result would be a severe loss of
vision or outright blindness. Charles Darwin knew about the eyes too.
In the origin of species Darwin dealt with many objections to his
theory of evolution by natural selection. He talked about the problem
of the eye in a section of the book entitled "Origins of Extreme
Perfection and Complication". In Darwin's thinking, evolution can't
build a complex organ in one one step or a few. Radical innovation such
as the eye would require generations of organisms to slowly accumulate
beneficial changes in a gradual process. He knew that if in one
generation an organ as complex as the eye just suddenly appeared, it
would be tantamount to a miracle. Unfortunately, gradual development of
the human eye appeared to be impossible since it's many sophisticated
features seemed to be interdependent. Somehow, for evolution to be
believable, Darwin had to convince the public that complex organs could
be formed in a step-by-step process. And he succeeded brilliantly.
Cleverly, Darwin didn't try to discover a real pathway that evolution
might have used to make the eye. Rather, he pointed to modern animals
with different kinds of eyes (ranging from simple to complex) and he
suggested that evolution of the human eye might have involved similar
organs as intermediates.
Here's a paraphrase of Darwin's argument: Although humans have complex
camera type eyes, many animals get by with less. Some tiny creatures
just have a simple group of pigmented cells not much more than a light
sensitive spot. The simple arrangement can hardly be said to confer
vision, but it can sense light and dark, and so it meets the creatures
need. The light sensing organ of some starfish are somewhat more
sophisticated. Their eye is located in a depressed region. Since the
curvatures of the depression block off light from some directions, the
animal can sense which direction the light is coming from. The
directional sense of the eye improves if the curvature becomes more
pronounced, but more curvature also lessens the amount of light that
enters the eye, decreasing it's sensitivity. The sensitivity can be
increased by placement of gelatinous material in the cavity to act as a
lens; some modern animals have eyes with such crude lenses. Gradual
improvement in the lens could then provide increasingly sharp images to
meet the requirement of the animals environment.
That is one of the ways that Darwin convinced many of his readers that
evolution leads from the simplest light sensitive spot to the
sophisticated camera eye of man. But the question of how vision began
remained unanswered. Darwin persuaded much of the world that a modern
eye evolved gradually from a simpler structure, but he didn't even try
to explain where his starting point - a relatively simple light
sensitive spot - came from. On the contrary, Darwin dismissed the
question of the eyes ultimate origin; "how a nerve comes to be
sensitive to light hardly concerns us more than how life itself
He was right to decline the question because he could not answer it.
(What happens when a photon of light hits the retina simply could not
be answered at that time, as a matter of fact, no question about the
underlying mechanism of life could be answered. How did animal muscles
cause movement? How did photosynthesis work? How was energy extracted
from food? How did the body fight infection? No one knew.)
Anyone who has ever tried to explain how evolution would have occurred
cannot explain how it came to be. They can only speculate. How is that
The eye is one of favorite examples because it can also not only be
explained through evolutionary theory but it also demonstrates the many
imperfections you would not expect to find if God had created it.
A typical argument of many creationists is that the eye is too complex
to evolve because, for it to work, every piece most work together. This
is a very simplified explanation but I think it will work for my point.
Let’s just imagine that there once lived a group of primitive animals
that had nothing more then light sensitive cell patches. No eyes. Over
time, a mutation in some of the individuals created a slight
indentation in these light sensitive cells. This indentation added a
new feature able to detect shadows, better for seeing potential
predators. Then over more time these shallow cups grew larger and
larger, further adding details to these shadows. Eventually these would
grow so large that they would essentially curve back in, creating a
sort of cone. Through this narrowing on one end the animals would now
able to detect, with creator accuracy the direction of it’s predator.
You also begin to move from shadows to images. Eventually the smaller
the hole becomes the greater the precision. Gradually leading towards
animals with pin drop sized holes. While there is some evidence of
ancestral species possessing pinhole eyes this is, however, much too
simplistic to describe human eyes.
Humans have eye lens, which complete matters. The lens is what allows
for greater clarity and detail. This also can evolve without a
designer. All an animal needed, for instance, was to have even a
protective coating of sorts around the eye. A kind of substance that
would be transparent enough to see shadows but strong enough to protect
the inner light cells of the eye. Over time, however, as the eye grew
in complexity, as described above, these transparencies might have
become a hindrance for clarity in visions. Over time, however, animals
that were able to contract and contrast these filmy layers were able to
get what is more or less the modern eye lens.
The eye is a great move in terms of evolution and has coevolved many
times before, independently. The latest example, if you remember, is
that crazy fish with those transparent eyes.
In addition the human eye has many flaws that you would not expect if there were a designer.
The most obvious design flaw of the retina is that the cellular layers
are backwards. Light has to travel through multiple layers in order to
get to the rods and cones that act as the photo-receptors. There is no
functional reason for this arrangement – it is purely quirky and
Even in a healthy and normally functioning eye this arrangement causes
problems. Because the nerve fibers coming from the rods and cones need
to come together as the optic nerve, which then has to travel back to
the brain, there needs to be a hole in the retina through which the
optic nerve can travel. This hole creates a blind spot in each eye. Our
brains compensate for this blind spot so that we normally don’t
perceive it – but it’s there.
The point is – a top-down designer could arrange the cells and the cell
layers in any configuration that could logically work, and it is
certainly possible to conceive of workable configurations that place
the photoreceptors at the top, rather than the bottom. Evolution, or a
bottom-up system, cannot do this. It is constrained by existing anatomy.
Another flaw are the blood vessels that feed the retinal sit on top of
the retina – between the light source and the receptive layer. A more
logical arrangement would be to have the blood vessels feed the retina
from behind, so that they do not get in the way. In healthy eyes the
blood vessels do not cause any perceptible problem (but they are also
partly responsible for the blind spot), but they do limit the total
amount of light reaching the rods and cones. The real problem is that
they are vulnerable to various diseases.
About 80% of diabetics who have had diabetes for 10 years will develop
diabetic retinopathy. In response to chronic ischemia (relative lack of
oxygen) the retina will produce chemical signals that tell the blood
vessels to proliferate to increase the blood supply. Because the blood
vessels are above the retina, they increasingly get in the way,
obscuring vision. At present the primary treatment of diabetic
retinopathy is to use a laser to burn some of the blood vessels and
decrease their proliferation.
Having the blood vessels in front of the retina also means that even a small retinal hemorrhage can significantly impair vision.
And finally, any edema or inflammation that occurs within the cell
layers in front of the rods and cones will likewise impair vision. All
of this could have been avoided or minimized were the rods and cones
placed in the most superficial layer of the retinal, rather than buried
at the bottom.
All features that could have been avoided had their been a designer.
One more thing about the eye. You cited a Darwin quote regarding the
eye that is ALWAYS misquoted and taken out of context by creationists.
"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." - Charles
Darwin, Origin of Species, 1st Ed., p. 186. "
I have read Origin of Species and I can assure you that Darwin wrote
this statement to set up an argument centered around debunking it. At
no time did he state that a creator must have made the eye.
Using this quote would be like taking a quote from a Christian that
says, "There is no evidence of God. Or at least that is what atheists
argue." And stating that the Christian said ".....There is no evidence
of God." The citation for all intensive purposes is not incorrect
however it is also not an accurate assessment of the Christian.
The rest of the quote, typically left out by creationists.
" When it was first said that the sun stood still and the world turned
round, the common sense of mankind declared the doctrine false; but the
old saying of Vox populi, vox Dei ["the voice of the people is the
voice of God "], as every philosopher knows, cannot be trusted in
science. Reason tells me, that if numerous gradations from a simple and
imperfect eye to one complex and perfect can be shown to exist, each
grade being useful to its possessor, as is certain the case; if
further, the eye ever varies and the variations be inherited, as is
likewise certainly the case; and if such variations should be useful to
any animal under changing conditions of life, then the difficulty of
believing that a perfect and complex eye could be formed by natural
selection, should not be considered as subversive of the theory."
Darwin then goes on for several more pages describing how the eye could
have formed in successive small steps from a small light-sensitive cell
to the fully developed human eye, documenting many examples of animals
with eyes in these successive states.