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| Schematic diagram of the human eye |
The vertebrate eye consists of five parts:
cornea (a transparent insulating layer); aqueous humor; crystalline lens (a lens
surrounded by muscles that make it possible to achieve a variable focal
length); vitreous humor; and retina. The light passes through the cornea and
the aqueous humor, is focused by the lens, goes through the vitreous humor and
impacts on the nerve cells of the retina, which generate electric signals that
the optic nerve transmits to the brain, which forms from them an image of the
external world, where the light rays came from. The brain even turns the image
around, as it is inverted when projected on the retina.
The complex structure of the eye has always
been a problem for evolutionists, and an argument for those opposed to the
theory of evolution. Darwin, in Chapter 6 of The Origin
of Species, whose title is significant (Difficulties of the theory)
dealt with the problem of the evolution of the eye in the following words:
Organs of extreme
perfection and complication. 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. 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...
In looking for the
gradations by which an organ in any species has been perfected, we ought to
look exclusively to its lineal ancestors; but this is scarcely ever possible,
and we are forced in each case to look to species of the same group, that is to
the collateral descendants from the same original parent-form, in order to see
what gradations are possible... Amongst existing Vertebrata, we find but a
small amount of gradation in the structure of the eye, and from fossil species
we can learn nothing on this head...
It is scarcely
possible to avoid comparing the eye to a telescope. We know that this
instrument has been perfected by the long-continued efforts of the highest
human intellects; and we naturally infer that the eye has been formed by a
somewhat analogous process... In living bodies, variation will cause the slight
alterations, generation will multiply them almost infinitely, and natural
selection will pick out with unerring skill
each improvement. Let this process go on for millions on millions of years; and
during each year on millions of individuals of many kinds; and may we not believe
that a living optical instrument might thus be formed as superior to one of
glass, as the works of the Creator are to those of man?
If it could be
demonstrated that any complex organ existed, which could not possibly have been
formed by numerous, successive, slight modifications, my theory would
absolutely break down. But I can find out no such case... We should be
extremely cautious in concluding that an organ could not have been formed by
transitional gradations of some kind.
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| Stanley Jaki |
Despite Darwin's reasoning, the eye remains one
of the organs that the supporters of the philosophical theory that has come to
be called intelligent design present as an
example of irreducible complexity, arguing that such a complex organ
cannot have arisen by natural selection from simpler intermediate phases,
because these would not have been functional, and therefore would not have
provided selective advantages to their owners.
Stanley Jaki attacked intelligent design with
these words:
The shortcomings,
often very serious, of Darwinian theory cannot be remedied with Intelligent
Design theory, which philosophically cannot cope with design and purpose. Moreover, it is a subtle rehash of the doctrine of
special creation. Even worse, as it claims to be a
"scientific" theory of evolution, it implies that design, insofar as
it means purpose (and indeed divine purpose) can be the object of measurements,
which is the touchstone of truth in science. S. L. Jaki, Intelligent
Design?, Real View Books, 2007.
However, Jaki himself uses the eye to assert
that the theory of evolution is far from complete, in his book The savior of science (1988-2000):
[The eye] has been
studied with far greater accuracy than any other organ. Exact measurements and
theories of physics have been added to anatomical studies of the eye to such
extent as to deprive Darwinists of their chief strategy: general if not vague
qualitative speculations about the specific steps of evolution. Yet they cannot
help admitting, without contradicting the exactness of physics, that, in the
words of one of them, “even if the slightest thing is wrong—if the retina is
missing, or the lens opaque, or the dimensions in error—the eye fails to form a
recognizable image and is consequently useless.” The quotation in the text is from G. Hardin, Nature and Man’s Fate, New
York: Rinehart and Company, pp.73-74.
The truth is that, in that quotation, Harding did
not act as a competent evolutionist. Please! Can we call slightest things a
missing retina or an opaque lens? It is evident that any of these "slightest
things" would turn the eye into a useless instrument. Compare this with asserting
that, in a car, if the slightest thing were wrong, such as missing the engine,
or having non-round wheels, the car could not fulfill its function.
Can we imagine in detail the evolution of the
eye, beyond general if not vague qualitative
speculations about the specific steps of evolution? Yes, we can.
But that will be the subject of the next post.
Manuel Alfonseca
I
thank John Beaumont, who suggested this series of four posts.
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