Seeing back to front
Are evolutionists right when they say our eyes are wired the wrong way?
‘No engineer worth his salt would design an eyeball the way ours has been built.’ So said evolutionist and popular-science writer Graham Phillips. 1 He was basing this on the very widely read book The Blind Watchmaker by Richard Dawkins. An Oxford zoologist who claims to have been a Christian before he really understood the implications of evolution, Dawkins is an outspoken opponent of creation and the supernatural in general. According to him, ‘some of the parts in our eyes have been wired backwards!’ 2
The retina in our eye (Fig. 1) is the light-sensitive layer, somewhat like the film in a camera. When the light rays forming a focused image fall on it, each of the millions of cells in it sends a signal to the brain along an individual nerve fibre, like an electrical wire.
A smart engineer, say evolutionists, would have these millions of ‘wires’ coming out the back of the retina, closest to the brain. Having the wiring coming out of the front seems to make no sense, they say, because this is the direction from which the light comes. Surely the light, having to pass through this tangle of cells and fibres (Fig. 2), must get distorted or weakened in some way?
Furthermore, because these ‘wires’ have to eventually get behind the retina in order to reach the brain, they have to plunge through a central hole in the retina; here they are bundled together to form the beginning of the optic nerve, on its way to the brain. 3 The eye of a squid or octopus is supposedly a lot like ours; but it is ‘wired correctly’ by Dawkins’ criterion, since its nerve fibres come out the back of the retina. Such critics overlook the fact that the cephalopod eye is actually more like ‘a compound eye with a single lens’, and doesn’t see as well as ours despite its ‘correct’ wiring.
Not only does our eye have the wires coming out the front; Fig. 2 shows that the light-sensitive parts of the visual receptor cells (the rods and cones) face backwards, away from the incoming light, where they butt against the opaque pigment layer.
Blind Chance Seeing Eyes
Evolution is supposed to proceed in a ‘blind’ way, without the ultimate goal in view. Evolutionists say they can conceive of an original clumsy ‘proto-eye’ (perhaps just one or a few light-sensitive cells), beginning by chance in this ‘back-to-front’ orientation, at a time when this made no difference. Once the eye started along its evolutionary path, it could not go ‘backwards’ and redesign from scratch, since everything has to happen in small steps in which each stage improves upon what went before.
This allegedly unwise design of the human eye, they say, fits the idea of a chance evolutionary process, able only to slightly modify an already existing design, not looking to any ultimate purpose millions of years hence. The eventual results will be ‘good enough’, but not necessarily perfect or the most sensible way to achieve the goal. Yet an intelligent Creator designing the eye to function immediately would not have left such marks of illogical design imperfection, we are told.
However, those many people who have been swept along by Dawkins’ argument should have first paused to see the breathtaking audacity of the claim. Let us leave aside for the moment ideas of what seems aesthetically nice. Could anyone really seriously claim that (in terms of how it brilliantly carries out its function) our eye demonstrates anything but superb precision and perfection?
There is in fact no evidence at all that having this layer of nerve fibres (which are largely transparent) in front of the receptors significantly blocks, distorts or diffracts the incoming light in any way. 4 This leaves evolutionists with only the flimsiest of claims; that is, that there seems to be no reason for it to be designed in this way.
However, that is not true. (Even if it were, it could either mean that we had not yet discovered the reason, or that the Creator simply chose to design it this way. In any case, the eye works beautifully; a design which merely seems ‘odd’ by our assessment cannot logically constitute proof of evolution or evidence against creation. 5 )
A Useful Filter
The human eye actually discriminates better in indirect, lower intensity light, so the intervening layer acts as a filter, minimizing excessive light-scattering. It also filters the short-wave ultraviolet (potentially cancer-causing) light. So why does the squid’s eye not have this ‘protective wiring’ up front? Because this creature operates in a different environment. 6 It needs all the light it can get, and because of the low intensity of UV light in water, neither sunburn nor sun cancers are occupational hazards for a squid or octopus. Both types of eyes are beautifully designed to suit their purpose.
But what about the way in which the rods/cones have their light-sensitive ends hard up against the pigment layer, facing away from the incoming light? Is there any conceivable reason for this? There certainly is. When light is shining on them, the granules of pigment from this layer migrate within little extensions (shown in Fig. 3) between the light-sensitive processes. This is very effective in screening scattered light (the granules return to the pigment layer in the dark).
Back Is Beautiful
According to biologist Richard Lumsden, it is critical to have the photoreceptive processes of the rods and cones intimately associated with the pigment layer for another reason, in order to allow the light-sensitive pigment rhodopsin to regenerate. 7 So if the rods and cones were turned around to face the incoming light, as Dawkins requires, the pigment layer would have to be between the light and the light receptors, thus blocking vision altogether! 8 In short, it is just as well that God, not Professor Dawkins, designed the e ye.
Fascinating Eye Facts
Eyes in different creatures are designed to meet their differing needs. Humans need good resolution and detail, whereas a fly needs speed. We see a fluorescent lamp as flickering at 10 Hz (cycles per second) but it looks stable to us at 20 Hz. A fly can detect a flicker of 200 Hz, so a normal movie would look to it like a slide show!
The simple act of walking into a room and immediately recognizing all the objects in it requires more computing power than a dozen of the world’s top supercomputers put together.
References and Notes
- ‘Mother Nature, the Imperfect Designer’, Sunday Telegraph (Sydney), September 26, 1993, p. 149.
- This is seen as a round whitish patch when a doctor looks into the back of your eye with his light. Because that part of the retina can’t form an image, we all have a tiny ‘blind spot’. This is so functionally insignificant that most of us are unaware that we have it (until its existence is demonstrated by simple experiment).
- Richard Lumsden, ‘Not So Blind a Watchmaker’, Creation Research Society Quarterly, 31:13–21, June 1994. Lumsden goes into more technical detail than we do here.
- See Walter ReMine’s classic book The Biotic Message for some really fascinating philosophical arguments on the thesis that alleged ‘imperfections’ of design such as the panda’s thumb are actually arguments against evolution. Evolutionist allegiance to the ‘blind watchmaker’ is a convenient philosophical ‘win-win’; they use ‘imperfect’ design to argue against a Creator, but the myriad examples of ‘perfect’ design do not lead them to acknowledge His handiwork (Romans 1:20).
- The human eye operates at the 400–700 nanometer (nm) range of wavelength, whereas the squid’s eye can operate as well in the 300 nm range, meaning it can ‘see’ with UV light. Ref 4.
- Lumsden also claims that the existing arrangement serves to shield the photoreceptive processes from toxic metabolites, though he does not elaborate.
- It is also crucial that these cells, with their very high rate of metabolic turnover, are supported by a very rich blood supply. In the current design, this is achieved by a dense capillary network in what is called the choroid layer, just outside of the pigment layer where it does not block any incoming light.