One of the hallmarks of so-called Intelligent Design is a concept called Irreducible Complexity. The idea is that there are some biological structures or systems that are more than the sum of their parts, such that it is improbable that they evolved from simpler structures. Each piece of the system is necessary to the functioning of the whole, while each individual piece is of little use by itself. To put it another way, an incomplete structure of this sort provides no survival or reproductive benefit.
One of the most celebrated example of this is the eye. This is a system that is seemingly irreducibly complex, such that is unlikely that its parts could have developed other than as a complete system. This is the claim made by many creationists, anyway. For example, the website “Darwinism Refuted” describes the “40 or so basic components” of the eye, each of which needs to be present for the eye to function properly. The retina alone, the sites states, is made up of 11 different strata, each of which has a function to perform, each of which is necessary to the function of the eye.
I do not intend to attack this concept directly; there are plenty of books, articles, and websites which do a far better job of it. Instead, I intend to pursue a line of inquiry suggested by Dr. Francis Collins in his book, “The Language of God.” Dr. Collins notes: “The design of the eye does not appear on close inspection to be completely ideal. The rods and cones that sense light are the bottom layer of the retina, and light has to pass through the nerves and blood vessels to reach them.” (Collins 2006, 191) Another related problem is the blind spot created where the optic nerve passes through the retina and the nerves spread out to make contact with the photoreceptors.
Vertebrate vs. Octopus Eyes
In vertebrate eyes (on the left), the nerve fibers route before the retina, blocking some light and creating a blind spot where the fibers pass through the retina and out of the eye. In octopus eyes (on the right), the nerve fibers route behind the retina, and do not block light or disrupt the retina. In the example, (4) denotes the vertebrate blind spot, which is notably absent in the octopus eye. In vertebrates, (1) denotes the retina and (2) the nerve fibers, including the optic nerve (3), whereas in octopodes, (1) and (2) denote the nerve fibers and retina respectively.
Take a look at the diagram above. On the left is the vertebrate eye; on the right is the eye of the Octopus. The vertebrate eye has what is called an inverted retina, with the photoreceptors behind the nerves, resulting in a blind spot where the optic nerve penetrates the retina. The Octopus eye has a much better design, with the nerves behind the photoreceptors and exposed to the light, such that even the area where the optic nerve penetrates the retina is covered with light-sensing cells, resulting in better vision and no blind spot.
In the vertebrate vision system, the brain interpolates the missing information from the blind spot by using information from the other eye. This presumes overlapping fields of vision, such as is typical with predatory animals. But prey animals, like horses, do not have overlapping fields of vision, and must rely upon a second method, using the eye’s constant movement to fill in for the blind spot.
The photoreceptors in the human eye respond to wavelengths corresponding to Red, Green, and Blue. Our perception of colors is an artifact of our brain — the result of computationally intensive processing which converts the differential response to these three colors into the millions of colors we perceive.
Human vision spans the wavelengths from about 400 to 700 nanometers. Below 400 nanometers is what we call ultraviolet; above 700 nanometers is what we call infrared. If you look at the diagram below, you will see that the spectral sensitivity of the human eye varies wildly across the so-called visible spectrum. The diagram below demonstrates certain wavelengths that humans are extremely sensitive to, while others we don’t see well at all.
Mantis Shrimp: Extraordinary Eyes
Now notice how the color vision of the Mantis shrimp is markedly superior to our own. Human photoreceptors are sensitive to three wavelengths; the Mantis shrimp photorecepters are sensitive to twelve wavelengths, with a great deal of overlap. Not only do Mantis shrimp see a wider part of the spectrum, but they are also sensitive to polarized light and multispectral images. Recent studies have demonstrated that the remarkable photoreceptors of the Mantis shrimp allow them to perceive color without requiring the heavy processing of the vertebrate eye and its computationally intensive comparisions. (Morrison 2014)
It is curious that human beings, being the pinnacle of God’s creation, would be saddled with a less than stellar visual system. The structure of our eyes is less sophisticated than that of octopods, and we see color less well than some insects and other marine invertebrates like the Mantis shrimp. If the human eye is the product of Intelligent Design, why did the Designer see fit to bless the lowly invertebrates with better visual systems than our own?
Bibliography
Collins, Francis S. The Language of God. New York: Free Press, 2006.
Morrison, Jessica. “Mantis shrimp’s super colour vision debunked.” Nature. January 23, 2014. http://www.nature.com/news/mantis-shrimp-s-super-colour-vision-debunked-1.14578 (accessed June 30, 2014).