v1.2.2 / chapter 15 of 28 / 01 aug 08 / greg goebel / public domain
* Although critics strongly insist that Darwinian macroevolution cannot account for elaborate biostructures like the eye, all available evidence shows the evolution of the eye to be no particular problem, and continued skepticism in the face of such evidence is simply not justified by the facts or logic.
* Dawkins' computer simulation is amusing and even thought-provoking, but it still isn't persuasive enough to answer the challenge posed by the Reverend Paley about the creation of the eye. The idea that it could have emerged in a single step is completely contrary to Darwinism. Darwinism insists that the changes would have to occur in small steps from a pre-existing structure, with each step providing a survival benefit to the life-form featuring the change, or at least doing it no harm. There has to be a workable eye of some sort at each stage of the process. Critics insist that there is no way the eye could have evolved by Darwinian processes through a sequence of steps, saying: "What good is half an eye?"
Darwin himself, thorough as always, admitted in chapter six of THE ORIGIN OF THE SPECIES that the evolution of the eye was a challenge to his ideas:
BEGIN QUOTE:
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 degree.
END QUOTE
This comment is often cited by the critics, who are generally careful to leave out the rest of the statement, in which Darwin pointed out that the challenge evaporates once some homework is done:
BEGIN QUOTE:
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, can be shown to exist; if further, the eye does vary ever so slightly, and the variations can be inherited, which is certainly the case; and if any variation or modifications in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable to our imagination, can hardly be considered real.
END QUOTE [italics added for emphasis]
Darwin goes on in his thorough way to provide an outline of just how the eye could have evolved. Updating his argument, if only slightly, shows that there is evidence that the eye did emerge in a sequence of steps, from an early primitive state. There are single-celled animals with a little spot that is light-sensitive, able to do no more than see if there's light available in one direction or not. More sophisticated animals like, say, worms, have a set of simple photoreceptors in a cup, which gives some directionality to their vision; a vitreous filling could then be acquired to protect the simple eye. The next step is to develop an eye like a pinhole camera, with a small aperture casting a relatively sharp image on a grid of photoreceptors -- a retina; the coiled nautilus has precisely such an eye. It's not very efficient since the pinhole doesn't admit much light, but it will provide an image.
Given a pinhole camera eye, the eye would be better protected if there was a transparent film of some sort over the pinhole. The film would gradually morph through a series of changes into a lens system, giving the eye more light-gathering capability and ability to focus; continue such changes and the result is the camera-like human eye. The full spectrum of forms of eye is available in existing species of animals; in fact, George Gaylord Simpson claimed that this spectrum exists among the known snails all by themselves.
In 1994, two researchers, Dan-Erik Nilsson and Susanne Pelger of the University of Lund in Sweden, published a paper describing an analysis they had performed, in which they envisioned the evolution of a fish eye from a simple eyespot by steps of almost imperceptible 1% changes in various component parameters. The analysis was based on conservative assumptions; it determined that it would take 1,829 steps to go from a simple eyespot to a fully-developed fish eye, and that this could happen in about 364,000 generations. The paper took the existence of an initial eyespot for granted, but this is not seen as a particular challenge: a simple eye can consist of nothing more than a nerve cell coupled to a skin cell loaded with a photosensitive pigment. Initially, the pigment might not have been all that efficient, but in time natural selection could be expected to improve on matters.
The range of forms of eyes of living creatures punctures the challenge posed by the critics who ask: "What good is half an eye?" Dawkins likes to snarkily answer: "It's 1% better than 49% of an eye." What good is, say, 5% vision? Actually, a creature with a simple eyespot probably can't be said to have even that much vision, being only capable of telling light from dark, but that capability is hardly useless. 5% vision is vastly better than no vision at all. Think of Bob wandering around on a dark but starry night outside of town, at least able to pick out trees and houses. Now compare that to Bob trying to poke around in the dark on a similar but overcast night, where he can't see his hand in front of his face. We only have about 5% vision at our periphery, but that's enough to have saved us from being run down by a bus on occasion.
In short, the notion of a succession of forms to create an eye is by no means unreasonable. It also should be noted, as would be expected in Darwinism, that there ends up being more than one way to make an eye. An octopus or squid has camera-like eyes as sophisticated in most respects as the human eye, but the details of construction are different. Of course, evolution has also moved off in entirely different directions to obtain eyes, for example the compound eyes of insects -- essentially a set of simple eyes, or "ommatidia", arranged over the surface of a hemisphere. Spiders, incidentally, don't have compound eyes; they usually have eight camera eyes, two large ones for primary vision and the other smaller ones for peripheral vision, though some species don't have the primary eyes. Some scallops and clams even have eyes like reflecting telescopes, with a rear mirror surface reflecting light to a retina up front.
* Critics will insist that the spectrum of forms of the eye found in nature does not in itself provide proof of the evolutionary succession of forms in the past, and that theoretical models of such an evolutionary succession are fictions. These assertions are true, but the original challenge was that the Darwinian evolution of the eye was clearly impossible, "unimaginable", and so the eye had to be the result of Design. The fact is that it can be imagined in details that are entirely plausible in terms of our knowledge of biology. That in itself demolishes the credibility of the eye as clear evidence of Design.
As far as the demand for absolute proof goes, in the natural sciences the term "proof" simply amounts to "evidence persuasive enough to establish the credibility of a proposition." There is no such thing as absolute proof in the natural sciences, since the possibility of an exceptional event, undiscovered and unknown evidence, errors in observation, conspiracies to suppress the facts, and so on can always be raised. It would be impossible for Alice to convince Bob that the Moon is made of rock if Bob was determined to insist that it was made of green cheese. The question is not one of absolute proof, but of the balance of credibility between offered explanations. Is the Moon made of rock, or green cheese? Put the evidence on the scales, and whether Bob wants to admit it or not, there's no question of which way the balance is going to tilt.
In terms of the evolution of the eye, the demand for more proof is just "moving the goalposts", a ploy of demanding that nothing less than taking a time machine back through history and obtaining a full set of biosamples would do the job, with all other evidence conveniently dismissed. At this point the critics would have to be asked why they think there are so many different forms of the eye in the world around them -- not just simple eyes ranging to complicated eyes, but even clearly different forms of complicated eyes, such as the human versus the squid eye. As Darwin put it, the only thing they could say is that "so it is; that it has so pleased the Creator" to build an eyespot or a nautilus eye or scallop eye or a human eye or a squid eye.
Such a response would leave the critics unable to press for more details without being asked why they seemed so unworried about the details of their own views -- and why a "just so" story is unacceptable while a "just because" story isn't.
* It is obvious that there are those who will not accept Darwinism no matter how much evidence is offered for it. In 1925, the Reverend William A. Williams, an American cleric, published a work titled THE EVOLUTION OF MAN SCIENTIFICALLY DISPROVED IN 50 ARGUMENTS, in which the author claimed to "mathematically disprove" Darwinism. He actually properly cited the comments by Darwin about the evolution of the eye, though only to register his disbelief:
BEGIN QUOTE:
Darwin undertakes a task too great for his mighty genius. "Believing that a perfect and complex eye could be formed" is many moral leagues from proving that it was so formed ... We hold evolutionists to the necessity of proving that the eye was certainly so formed. We demand it ...
END QUOTE
After this dramatic declaration, he then went on to give a mathematical "disproof" that ends up being a bit of an anticlimax:
BEGIN QUOTE:
There are 2,500 to 3,500 square inches of surface to the human body, a space easily 3,000 times the space of the eye. The eye, by the laws of probability, is just as likely to be located any where else, and has one chance in 3,000 to be located where it is. But out of our abundant margin, we will concede the chance to be one out of 1,000, and so its mathematical probability is .001 ...
END QUOTE
The Reverend Williams went on in this vein to establish the probabilities of the location of the other eye, the ears, and so on to finally multiply them together and show that the odds of simply throwing everything together and having it all be so neatly organized were vanishingly small. In other words, he was using a "monkeys & typewriters" model of Darwinian evolution and had no clear idea of how Darwinism actually worked. The Reverend Williams has been generally forgotten, but he appears to have been one of the first to present an extended argument against Darwinism based on probability calculations. He wouldn't be the last, though the argument would still often be along the lines of "monkeys & typewriters", just rephrased in various ways.
The Reverend Williams also attempted with his mightier genius to show the size of the human population in the 1920s ruled out an old Earth, since if human population had been doubling for millions instead of thousands of years, the Earth would have run out of space for humanity long before. Using the same logic, anyone with pencil, paper, and log tables could have shown him that if mice doubled their number every year -- without running into a population ceiling, as Darwin learned from Malthus all population growth inevitably would -- the Earth would be completely carpeted with mice in about 60 years, and about 30 years later the mass of the mice would exceed that of the entire planet. Obviously, the Earth couldn't be a century old. Surprisingly, despite the gaping hole in the logic of this argument, it still remains in circulation.
* The Reverend Williams' hamfisted math was rooted in a subtler misunderstanding: the failure to realize that though implausibility demands sensible skepticism and scrutiny, it is not proof of falsehood. The sciences tend to defy our preconceptions, sometimes in drastic ways. As J.B.S. Haldane once commented, the Universe is not only stranger than we imagine, it is stranger than we can imagine.
The laws of nature are not subject to human likes and dislikes in the slightest way. What reason do we have to assume, much less demand, that reality should be simple to understand? If the Universe is in fact a construction, we were not consulted on how it was to be put together, and we have no means of submitting a complaint form if we don't like it.
Any examination of the conventional wisdom of the past shows that what was regarded as "obvious" turned out in many cases to be spectacularly wrong. People once thought the Sun orbited around the Earth, and though we all know that's not the way things work, from our parochial point of view the Sun flatly seems to go around our world, rising in the morning and setting at night while we have no perception of moving at all. They were outraged at the notion that it was instead the Earth that moves around the Sun; but for all their protests, "it moves nonetheless."
"Haldane's law", as his comment is sometimes called, clearly applies to many other theories in science. Albert Einstein's theory of special relativity says that time slows down in a moving object: one twin who takes a starship from Earth to a distant world and then comes back home will age less than the twin who stayed home. The idea seems contradictory, but it logically holds up under skeptical analysis, has survived determined attempts to disprove it, and it is backed up by all available experimental evidence.
In quantum physics, there are phenomena that not only seem implausible, but seem so blatantly illogical that absolutely no sane person would believe they were for real, except for the fact that the experimental evidence absolutely demands it. The reaction of those who uncovered the evidence was: This can't possibly be right! -- but every single attempt to prove otherwise failed. Edward Millikan, a meticulous experimental physicist, conducted careful experiments for several years with the intent of disproving the quantum mechanical basis of light as postulated by Einstein, and ended up being forced to believe it despite its "fundamental unreasonableness". Even Einstein admitted to the end of his life that his postulate of the quantum light particle, what would become known as the "photon", was baffling in many ways, but was and remains the only way to account for the evidence, and there is no real dispute over the matter.
A student of the great American physicist Richard P. Feynman indicated disbelief at quantum physics, to which Feynman replied: "Well, go do the experiments until you do believe it." Once skepticism has been met by a body of clear and solid evidence, further insistence on the disagreeableness of an idea no longer has any bearing on the facts: like it or not, it moves nonetheless.
Rephrasing what the great Danish physicist Niels Bohr said about quantum mechanics: anyone who is not shocked on learning about Darwinism hasn't understood it. However, like quantum physics, Darwinism is not going to go away simply because some find it disagreeable. The Darwinian evolution of organisms by natural selection is so thoroughly demonstrated in the evidence to make it, if not absolutely irrefutable for all time, at least overwhelmingly stronger than all available alternatives.
