Fish eye story in Live Science 28 June 2012 and Phys Org 29 June 2012. Scientists studying the Elephant Nose fish, a strange looking fish that lives in “dark, slow-moving, heavily vegetated waters in central and west Africa” have found it has a most unusual arrangement of photoreceptors in its eyes. Photoreceptors are the cells that convert light into electrical signals, which are then sent to the brain. Like most vertebrates the fish has two kinds of photoreceptors: rods and cones. Rods are able to function in dim light, but do not function in bright light. Cones work in bright light, but not dim light. The Elephant Nose fish retina has hundreds of cup-like structures lined with layers of guanine that act as photonic crystals (a complex of mirrored surfaces) directing the light at the base of the cup, where there is a group of cones. The reflective cups concentrate the light, so that even in the dim light of the murky water where the fish lives, the cones can function. The rods are located behind the cups and they pick up any light that passes right through the cups without being reflected. This arrangement enables the fish to use both types of photoreceptors together, and means that the fish can make the most of all the light that penetrates the water. It also means the fish cannot see fine details, but as it lives in turbid waters this is an advantage, as it can see large objects well, but is not distracted by bubbles or sediment in the water. Andreas Reichenbach, of Leipzig University, Germany, one of the researchers explained: “That’s the advantage the retina brings to the fish. If you or a hawk with its excellent eyesight would be where this fish lives you would see virtually nothing, but the fish can detect what they need to see”. The research team concluded their report: “We conclude that their grouped retina, as a unique type of retinal specialization, has emerged to provide the optical prerequisite to detect large, fast-moving predators as an adaptation to the survival demands of the fish’s habitat. It might be expected that similar evolutionary advantages rationalize the grouped retina found in other species”.
Editorial Comment: Did you note their argument: the fish has this unusual retina, it uses it for seeing big fish and it is preyed on by big fish – it therefore evolved the retina to survive. Only the first three statements are the testable science. The fact is this is a useful retina for a fish that lives in turbid water. However, that does not tell you how the retina came to have this structure. If it didn’t have it before the water went turbid, then it died out if it depended on seeing predators in turbid water. To believe that it just “emerged” to provide the fish with the ability to see large, fast moving predators requires a great deal of blind faith (if you can forgive the pun). Murky water and large predators have never been observed to change the genes of a fish without this retinal structure into genes required to make this retina.
The study of this fish retina is a good illustration of how easily we can recognise design. The reports about this fish described its retina as “unique”. That does not mean it has components no other fish retina has. Rods and cones are cells found in all vertebrate eyes, and the crystals in the cups are made of guanine – a chemical that exists in many other places. It is the organisation of the parts that makes this retina work – not the parts themselves. As part of their research into this retina the scientists came up with a mathematical model of how the crystal cups worked. This research and conclusion required intelligent scientists and a computer. Therefore, to believe the fish’s retina was designed and created by a smarter and more powerful Creator is anything but a Blind faith. Try to make a copy of this retina if you are still having trouble accepting the argument for design. You will find it requires tremendous creative design and technical expertise. (Ref. ichthyology, optics, vision)
Evidence News 18 July 2012