5. Considering each member of the series of Xs connecting the human eye to no eye at all, is it plausible that every one of them worked sufficiently well that it assisted the survival and reproduction of the animals concerned?
Rather oddly, some people have thought that the answer to this question is a self-evident 'no'. For instance, I quote from Francis Hitching's book of 1982 called The Neck of the Giraffe or Where Darwin Went Wrong. I could have quoted basically the same words from almost any Jehovah's Witness tract, but I choose this book because a reputable publisher (Pan Books Ltd) saw fit to publish it, despite a very large number of errors which would quickly have been spotted if an unemployed biology graduate, or indeed undergraduate, had been asked to glance through the manuscript. (My favourites, if you'll indulge me just two in-jokes, are the conferring of a knighthood on Professor John Maynard Smith, and the description of Professor Ernst Mayr, that eloquent and most unmathematical arch-critic of mathematical genetics, as 'the high priest' of mathematical genetics.)
For the eye to work the following minimum perfectly coordinated steps have to take place (there arc many others happening simultaneously, but even a grossly simplified description is enough to point up the problems for Darwinian theory) The eye must be clean and moist, maintained in this state by the interaction of the tear gland and movable eyelids, whose eyelashes also act as a crude filter against the sun The light then passes through a small transparent section of the protective outer coating (the cornea), and continues via a lens which focuses it on the back of the retina. Here 130 million light-sensitive rods and cones cause photochemical reactions which transform the light into electrical impulses. some 1,000 million of these are transmitted every second, by means that are not properly understood, to a brain which then takes appropriate action.
Now it is quite evident that if the slightest thing goes wrong en route - if the cornea is fuzzy, or the pupil fails to dilate, or the lens becomes opaque, or the focussing goes wrong then a recognizable image is not formed. The eye either functions as a whole, or not at all. so how did it come to evolve by slow, steady, infinitesimally small Darwinian improvements? Is it really plausible that thousands upon thousands of lucky chance mutations happened coincidentally so that the Iens and the retina, which cannot work without each other, evolved in synchrony? What survival value can there be in an eye that doesn't see?
This remarkable argument is very frequently made, presumably because people want to believe its conclusion. Consider the statement that 'if the slightest thing goes wrong . . . if the focusing goes wrong . . . a recognizable image is not formed'. The odds cannot be far from 50/50 that you are reading these words through glass lenses. Take them off and look around. Would you agree that 'a recognizable image is not formed'? If you are male, the odds are about 1 in 12 that you are colourblind. You may well be astigmatic. It is not unlikely that, without glasses, your vision is a misty blur. One of today's most distinguished (though not yet knighted) evolutionary theorists so seldom cleans his glasses that his vision is probably a misty blur anyway, but he seems to get along pretty well and, by his own account, he used to play a mean game of monocular squash. If you have lost your glasses, it may be that you upset your friends by failing to recognize them in the street. But you yourself would be even more upset if somebody said to you: 'Since your vision is now not absolutely perfect, you might as well go around with your eyes tight shut until you find your glasses again.' Yet that is essentially what the author of the passage I have quoted is suggesting.
He also states, as though it were obvious, that the lens and the retina cannot work without each other. On what authority? Someone close to me has had a cataract operation in both eyes. She has no lenses in her eyes at all. Without glasses she couldn't even begin to play lawn tennis or aim a rifle. But she assures me that you are far better off with a lensless eye than with no eye at all. You can tell if you are about to walk into a wall or another person. If you were a wild creature, you could certainly use your lensless eye to detect the looming shape of a predator, and the direction from which it was approaching. In a primitive world where some creatures had no eyes at all and others had lensless eyes, the ones with lensless eyes would have all sorts of advantages. And there is a continuous series of Xs, such that each tiny improvement in sharpness of image, from swimming blur to perfect human vision, plausibly increases the organism's chances of surviving.
The book goes on to quote Stephen Jay Gould, the noted Harvard palaeontologist, as saying:
we avoid the excellent question, What good is 5 percent of an eye? by arguing that the possessor of such an incipient structure did not use it for sight.
An ancient animal with 5 per cent of an eye might indeed have used it for something other than sight, but it seems to me at least as likely that it used it for 5 per cent vision. And actually I don't think it is an excellent question. Vision that is 5 per cent as good as yours or mine is very much worth having in comparison with no vision at all. So is 1 per cent vision better than total blindness. And 6 per cent is better than 5, 7 per cent better than 6, and so on up the gradual, continuous series. This kind of problem has also worried some people interested in animals that gain protection from predators by 'mimicry'.
