Does an objective look at the human eye show evidence
Perhaps the most frequently raised criticism of
evolution in any evolution-creation debate is that of the human
eye. The creationist will say something like, "How can something
as marvelous as the human eye have come about by chance alone? Surely
there must have been a divine creation." These types of statements
show two things. First, the creationist doesn't understand how evolution's
'chance' works. (i.e. They have yet to grasp the fact of cumulative
natural selection.) Second, they haven't bothered to really examine
the human eye to look for characteristics such as design flaws.
(Note that the quote from Ernst Mayr under the above "creationist
will say" link has been taken completely out of context. Not
only does Mayr's entire book provide evidence after evidence of
"improved" random mutations, but the same paragraph as
quoted also states that "the objectors to random mutations
have so far been unable to advance any alternative explanation that
was supported by substantial evidence." This page looks at
the substantial evidence against the intelligent designer of creationism.)
As Frank Zindler, former professor of biology and geology, stated,
"As an organ developed via the opportunistic
twists and turns of evolutionary processes, the human eye is explainable.
As an organ designed and created by an infinitely wise deity,
the human eye is inexcusable. For unlike the invertebrate eyes
..., the human eye is constructed upon the foundation of an almost
incredible error: The retina has been put together backwards!
Unlike the retinas of octopuses and squids, in which the light-gathering
cells are aimed forward, toward the source of incoming light,
the photoreceptor cells (the so called rods and cones) of the
human retina are aimed backward, away from the light source. Worse
yet, the nerve fibers which must carry signals from the retina
to the brain must pass in front of the receptor cells, partially
impeding the penetration of light to the receptors. Only a blasphemer
would attribute such a situation to divine design! Although the
human eye would be a scandal if it were the result of divine deliberation,
a plausible evolutionary explanation of its absurd construction
can be obtained quite easily--even though we can make little use
of paleontology (because eyes, like all soft tissues, rarely fossilize)."
Biologist George Williams wrote an entire book on
the subject of design and purpose in nature. Near the beginning
of The Pony Fish's Glow, Williams responds to Paley's watchmaker
argument using various body parts as examples of why Paley's argument
may look good on the surface, but it lacks credibility when closely
examined using modern technology and biology. Here he discusses
the human eye:
"not all features of the human eye make
functional sense. Some are arbitrary. To begin at the grossest
level, is there a good functional reason for having two eyes?
Why not one or three or some other number? Yes, there is a reason:
two is better than one because they permit stereoscopic vision
and the gathering of three-dimensional information about the environment.
But three would be better still. We could have our stereoscopic
view of what lies ahead plus another eye to warn us of what might
be sneaking up behind. (I have more suggestions for improving
human vision in chapter 7.) When we examine each eye from behind,
we find that there are six tiny muscles that move it so that it
can point in different directions. Why six? Properly spaced and
coordinated, three would suffice, just as three is an adequate
number of legs for a photographer's tripod. The paucity of eyes
and excess of their muscles seem to have no functional explanation.
And some eye features are not merely arbitrary but clearly dysfunctional.
The nerve fibers from the retinal rods and cones extend not inward
toward the brain but outward toward the chamber of the eye and
source of light. They have to gather into a bundle, the optic
nerve, inside the eye, and exit via a hole in the retina. Even
though the obstructing layer is microscopically thin, some light
is lost from having to pass through the layer of nerve fibers
and ganglia and especially the blood vessels that serve them.
The eye is blind where the optic nerve exits through its hole.
The loose application of the retina to the underlying sclera makes
the eye vulnerable to the serious medical problem of detached
retina. It would not be if the nerve fibers passed through the
sclera and formed the optic nerve behind the eye. This functionally
sensible arrangement is in fact what is found in the eye of a
squid and other mollusks (as shown in the figure below), but our
eyes, and those of all other vertebrates, have the functionally
stupid upside-down orientation of the retina.
A. The human eye as it ought to be, with
a squidlike retinal orientation. B. The human eye as it
really is, with nerves and vessels traversing the inside
of the retina.
Paley did not really confront this problem. Little
was known about mollusks' eyes at the time, and Paley merely treated
the blind spots as one of the problems the eye must solve. He
correctly noted that the medial position of the optic nerve exits
avoids having both eyes blind to the same part of the visual field.
Everything in the field is seen by at least one eye. It might
also be claimed that the obstructing tissues of the retina are
made as thin and transparent as possible, so as to minimize the
shading of the light-sensitive layer. Unfortunately there is no
way to make red blood cells transparent, and the blood vessels
cast demonstrable shadows.
What might Paley's reaction have been to the claim,
which I will elaborate in the next chapter, that mundane processes
taking place throughout living nature can produce contrivances
without contrivers, and that these processes produce not only
functionally elegant features but also, as a kind of cumulative
historical burden, the arbitrary and dysfunctional features of
organisms?" (page 9-10)
He continues on the eye later as follows:
"What would Paley's reaction have been to
the suggestion that the creator's wisdom is as finite as ours,
and that the engineering perfection of such instruments as the
eye...depends...on much trial-and-error tinkering that supplemented
the creator's limited understanding? And what about the suggestion
that the creator had no understanding at all, but accomplished
sophisticated engineering entirely on the basis of trial and error?"
Williams concludes his section on trial-and-error
and the eye argument with the following:
"This is no doubt true of all the implements
we use: cameras, cars, computers, and even the watch that Paley
reasoned must have had an intelligent designer. How far is it
possible to go with trial and error alone? All the way to the
human eye and hand and immune system and all the other well-engineered
machinery by which we, and all other organisms, solve the problems
of life... Darwin was challenged repeatedly on this matter. Critics
would point to the precision and design features of the eye and
claim that an organ of this perfection could not possibly have
been produced by an accumulation of small changes, each of which
made the eye work slightly better. A grossly imperfect eye, which
could be improved by this process, would supposedly never evolve
in the first place. Slight improvements in one part, such as the
retina, would be useless without an exactly matching improvement
in another, such as an increased precision of the lens. This is
an utterly fallacious kind of reasoning. An improved retina may
be useless without an improved lens, but both retinas and lenses
are subject to individual variation. Some of the better retinas
would be found in individuals who also had better lenses, so that
the improvements, on average, could be favored.
The criticisms were also factually erroneous,
and their proponents were ignorant of biology. As Darwin pointed
out, familiarity with the animal kingdom shows the existence today
of just about every stage in a plausible sequence from primitive
light-sensitive cells on the surfaces of tiny wormlike animals,
through the rudimentary camera eyes of scallops, to the advanced
optical instrumentation of squids and vertebrates. Every stage
in this sequence is subject to variation, and every stage is clearly
useful to its possessor." (page 13-14)
Another creature to consider is the mole rat. Which
theory holds water when the eye of the mole rat is considered? The
ancestor of the mole rat presumably used its eyes as it lived above
ground and needed them for survival. However, the mole rat has adapted
to living underground in complete darkness. Its eyes have become
useless--indeed, they have been buried beneath skin and fur and
couldn't be used even if the mole rat came into the light. The neurons
that were used for sight have been put to better use in the mole
rat's brain for other sensory functions. Evolution by natural selection
perfectly explains the eyes of a mole rat. A creationist must resort
to faith and/or a poor designer.
See Lucy's Legacy p. 25 and Jared Diamond's
"Competition for brain space" in Nature 382: 756-757.
Those interested in this subject should also see
- chapters four and five of Richard Dawkins' Climbing
- section 13.3 in Mark Ridley's Evolution,
- pages 110 to 114 in Cells, Embryos, and Evolution,
- Ted Gaten's research interests, and
- How Could An Eye Evolve?
On a related topic, see the inefficiencies created
by natural selection (and lack of design) as illustrated on this
In summary, the eye not only lacks evidence of divine
creation, it exemplifies the problems that natural evolution can
create (along with the virtues) in organisms. Rather than being
a chief argument for creationism, the human eye should be a topic
that 'special creation' apologists avoid.