eye

Did eyes evolve by Darwinian mechanisms?

The evolution of the eye has always been a dilemma for evolutionists from Darwin’s time to the present. Although Darwin, Richard Dawkins and other evolutionists have tried to explain how an eye could evolve, their solutions are clearly unsatisfactory. Many kinds of eyes exist, but no progression of eye designs from simple to complex can be produced in the natural or fossil world. Furthermore, the simplest ‘eye’, the eyespot, is not an eye but pigmented cells used for phototaxis; yet even it requires an enormously complex mechanism in order to function as a vision system.

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The concept of irreducible complexity (IC) has become an important tool in intelligent design theory. One of the best examples of IC is the design of the animal eye. Eyes are critical because, for the ‘vast majority of animals’, vision is their ‘most important link to the world’.1 Darwin vividly recognized the problem of eye evolution and the serious impediment that it was for his theory. In his words,

‘To suppose that the eye, with all its inimitable contrivance 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.’2

Nonetheless, Darwin felt the seemingly insurmountable problem of the evolution of what he called an organ of ‘extreme perfection and complication’ could be solved.2 He included a three-page proposal of intermediate stages through which eyes might have evolved via gradual steps.3 These stages included the following:

  1. photosensitive cell
  2. aggregates of pigment cells without a nerve
  3. an optic nerve surrounded by pigment cells and covered by translucent skin
  4. pigment cells forming a small depression and then a deeper depression
  5. the skin over the depression gradually taking a lens shape
  6. evolution of muscles that allow the lens to adjust.

These stages in living animals are believed to constitute major evidence for the evolution of the eye.4 Isaak claims that all of these steps are viable because all of them exist in animals living today:

‘The increments between these steps are slight and may be broken down into even smaller increments. Natural selection should, under many circumstances, favor the increments. Since eyes do not fossilize well, we do not know that the development of the eye followed exactly that path, but we certainly cannot claim that no path exists.’5

University of Chicago biology Professor Jerry Coyne wrote that human

‘ … eyes did not suddenly appear as full-fledged camera eyes, but evolved from simpler eyes, having fewer components, in ancestral species. Darwin brilliantly addressed this argument by surveying existing species to see if one could find functional but less complex eyes that not only were useful, but also could be strung together into a hypothetical sequence showing how a camera eye might evolve. If this could be done—and it can—then the argument for irreducible complexity vanishes, for the eyes of existing species are obviously useful, and each step in the hypothetical sequence could thus evolve by natural selection.’6

The dominant theory was outlined by Dennett, who concluded that all eye evolution requires is a

‘ … rare accident giving one lucky animal a mutation that improves its vision over that of its siblings; if this improvement helps it to have more offspring than its rivals, this gives evolution an opportunity to raise the bar and ratchet up the design of the eye by one mindless step. And since these lucky improvements accumulate—this was Darwin’s insight—eyes can automatically get better and better and better, without any intelligent designer.’7

Others are not so confident. Melnick concluded that the eye is a marvel and that ‘its immense complexity and diversity in nature, as well as its beauty and perfection in so many different creatures of the world, defies explanation even by macroevolution’s most ardent supporters.’8 This paper explores these conflicting views.

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Evolution of the eye

Advanced vision appears almost at the very beginning of the fossil record. The oldest eye in the fossil record, that of a trilobite, is a very complex faceted compound eye that ‘dates’ back to the Cambrian, conventionally dated about 540 million years ago.9,10 The fossil evidence shows that from the beginning of the fossil record eyes are very complex, highly developed structures. We also have ‘living fossils’, animals that have remained virtually unchanged since very early in history. University of Salford biologist, Laurence R. Croft, wrote that the ‘precise origin of the vertebrate eye is still a mystery. The fascinating thing about the evolution of the eye is its apparent sudden appearance.’11 Specifically, the fossils show that vision originated ‘in the early Cambrian’, which Darwinists put at ‘some 530 million years ago’.12

Furthermore, although the ‘Cambrian animals were not the same species as exist today … nearly all the modern phyla had rapidly come into existence, fully equipped with eyes as far as can be told from the fossils’ and during the Cambrian explosion ‘something remarkable seems to have happened … a rich fauna of macroscopic animals evolved, and many of them had large eyes.’12 Sir Steward Duke-Elder, the preeminent ophthalmologist at the time of his death in 1979, acknowledged the sudden appearance of the perfected vertebrate eye, noting:

‘The curious thing, however, about the evolution of the vertebrate eye is the apparent suddenness of its appearance and the elaboration of its structures in its earliest known stages. There is no long evolutionary story as we have seen among invertebrate eyes, whereby an intracellular organelle passes into a unicellular and then a multicellular eye, attaining by trial and error, along different routes an ever-increasing degree of complexity. Within the vertebrate phylum the eye shows no progress of increasing differentiation and perfection as is seen in the brain, the ear, the heart and most other organs. In its essentials the eye of a fish is as complex and fully developed as that of a bird or man [emphasis added].’13

Biochemical studies have shown that the human lens contains

‘ … proteins similar to those found in the cyclostomes (hagfishes and lampreys) that are the living descendants of the Agnatha, which originated the vertebrates about 450 million years ago. Thus these studies have confirmed the view that the vertebrate eye, and in particular the lens, has changed very little during the course of evolution.’14

Evidence for eye evolution from living animals

Only about a third of all animal phyla contain species with proper eyes, another third contain species with light-sensitive organs only, and a third have no means of light detection, although many can detect heat.15 Nonetheless, of those animals with eyes, both vertebrates and most invertebrates, an enormous variety of eye designs, placement and sizes exists.10 The eyeball diameter ranges from less then a tenth of a millimetre in certain water fleas to 370 mm in the giant squid.16 Eye placement also varies, ranging from the common binocular vision employed by most mammals to the movable eye on each side of the head used by many lizards.

The number of eyes in one animal can also vary from none to eight. In spiders alone the number ranges from zero to eight, always existing in pairs of two. Some eyes contain both a lens and a retina-like structure in a single cell.17 A complex telephoto lens was identified in the chameleon in 1995. The reason why so many designs exist is because eyes must serve very different life forms that live in very different environments. Animals live in the ground, inside of other animals, in the air, on land, in salt water and in fresh water. Furthermore, animals range in size from a water flea to a whale.

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Source: creation.com

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