Nature can be thought of as a blind knob-twiddler, an unconscious sculptor that chisels the gene pool, without any goal or purpose in mind. The process of natural selection acts, a posteriori, on preexisitng traits that have a heritable genetic component. A random variation of a heritable basis means that beneficial traits will emerge, which ultimately leads to such a process of non-random selection of randomly varying genetic equipment. The effects of selection, thus, produce a sort of illusion of design and false teleological implications as a consequence.

Not all variation is adaptive variation. Variation is a function of differential environmental heterogeneity. Variation itself is, also, non-directed and indeed, not all variation is adaptive. The environment only mediates a certain selection mechanism that tends in an adaptive fashion. It is the environment that provides the only source of directedness onto which evolutionary change proceeds.

Arguments against evolution tend to always single out a particular organ or biological system and use complexity to make the case for deliberate design by some sort of an intelligent agency. Aside from the fact that such an argument presupposes the existence of an even more remarkably complex entity and therefore creates more questions than it answers, it is flawed for many other reasons. It is an evasion of the responsibility to explain such complexity by thrusting forwards a mere presupposition that cannot be tested and does not have any observable consequences. And, secondly, it presupposes that complexity must mean design, shortsightedly basing such a presupposition on analogies of design by humans.

Intelligent design advocates always like to misinterpret Charles Darwin, when he wrote in The Origin of Species, that “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.” Little, however, do they always go on with the rest of the quote when Darwin, thereafter, remarks: “Reason tells me, that if numerous gradations from a simple and imperfect eye to one complex and perfect can be shown to exist, each grade being useful to its possessor, as is certainly the case; if further, the eye ever varies and the variations be inherited, as is likewise certainly the case; and if such variations should be useful to any 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 by our imagination, should not be considered as subversive of the theory”.

Natural selection is more of a tinkerer than a designer (Monod, 1971). It works with what is available and while it does not lead to optimum results, it still gets the job done. The claim that an organ like the eye is perfectly designed is very flawed. The eye is, in fact, very poorly designed. Photosensitive cells point inwards away from the source of light such that light has to pass through the nerves and blood vessels and while it does, it degrades in the process. Further, an opening in the retina exists (called the blind spot) where nerve fibres pass through to the brain and where no rods and cones exist and therefore no image is focused. An engineer designing a television where a hole has to be constructed in the middle such that the wires pass through is a very bad engineer. In the vertebrate eye, the wires lie all over the surface of the retina and the photosensitive cells. And, the photocells are very loosely bound to the retina such that they can be detached easily after a trauma.

By contrast, other animals have very well-constructed eyes. The giant squid, for instance, has an eye where the photoreceptors point towards the light and where the nerves lie behind the retina and thus, where the optic nerve does not have to get in the way of the retina. Indeed, cephalopod eyes originate as a skin derivative rather than derive from the brain as they do in vertebrates. The same is true for pelagic fish. Such adaptations allow cephalopods and pelagic fish to target their prey in darkness. In addition, hawks can see much further than humans because they have a much greater density of light-sensitive cells. And, molluscs have mirrors instead of lenses.

Insects and crustaceans have compound eyes which are much more efficient at capturing light than vertebrate eyes. Compound eyes have hundreds or thousands of mini eyetubes (called ommatidia) radiating out from a central point over a convex surface, each receiving light at a different angle and focusing it onto a group of 9 photoreceptors and each seeing a different patch of the world around them. The number of tubes can vary from 1 tube/eye in fleas to as much as 30,000 tubes/eye in dragonflies. In compound eyes, the image that is constructed is not an inverted image.