You Gotta Dance with Who Brung Ya to The Ball by Gaurang Bhatt, MD SignUp
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You Gotta Dance with Who Brung Ya to The Ball
by Gaurang Bhatt, MD Bookmark and Share
 

The title was a favorite expression of a University of Texas football coach and implies to stick with what works for you. I intend to clarify how it applies to evolution and politics.

If one were to ask an engineer to design a camera, she would begin with a closed box impervious to light and make a controlled diameter aperture to collect and control the incoming light. The next step would be to put a perfectly curved smooth lens behind the aperture which is capable of varying its focal length in such a way that the incoming light will always form an image exactly on the back wall containing a suitable photosensitive surface. If the image has to be transmitted some distance like to a control, analysis and security station, she would make sure that the cable takes off from behind the photosensitive back wall and the wires from pixels of the photosensitive screen are connected to an input to its back surface and definitely not arise from the light or image receiving inner surface of the back wall.

Evolution does not follow the intelligent design of an engineer or creator (see my article “Intelligent Design - A Trojan Horse”). It is a tinkerer and has to play with the cards it has been dealt. Thus the human eye is  a cumbersome design in which there are three cell layers in the retina or back wall and the outermost layer is the one with light sensitive photo-receptor cells containing the protein Rhodopsin which functions like a silver nitrate light sensitive film. The middle layer of bipolar cells receive and process the input from the outermost photo-receptor cell layer and relay it to the innermost ganglion cell layer whose fibers collect to form the image conveying cable, the optic nerve which proceeds to the security and analysis center called the visual cortex of the brain by penetrating the back wall and becoming a blind spot.

This requires that the inner two layer of cells be transparent to light, but it still leaves the problem of a small round area of the retina where the fibers collect to form the optic nerve being blind to light. The ultimate processing organ, the brain automatically fills in the image at the blind spot, leading to automobile accidents while changing lanes using the rear mirror. An unevenly machined cornea or lens, at the outermost front layer of the box is what causes astigmatism requiring spectacles. A lens losing its ability to alter focal length with age, requires the use of reading glasses. A lens becoming opaque due to aging or diabetes leads to cataract requiring surgery with lens implants. A faulty childhood development where the shape of the eyeball is not ideal makes the image fall short of the retina. Such shortsightedness is corrected by glasses, contact lenses or laser surgery.

Darwin had a tough time explaining the evolution of the eye. He said,

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 possible degree”.

In the animal kingdom there are many different types of eyes. Some primitive worms merely have a light sensitive patch of cells on each side of their front end and generally use them to shun light and hide in dark spaces.  Insects in general have what are called compound eyes which provide blurred vision but with a wider field of vision. A human with compound eyes would require each one to be a soccer ball size, to match the visual acuity of our camera eyes. Until two decades ago the scientific belief was that eyes evolved multiple times in evolution and it probably accounted for the different structure of eyes of different species. Squids and octopuses have camera type eyes but their photo-receptors are the insect type. Fish and  mammals (all jawed vertebrates) have two types of photo-receptors, cones for sharp daylight seeing and rods for nighttime seeing when light is poor.

Then a gene named eyeless (or aniridia, also called ey) was found and a defective ey gene led to a failed eye development in fruit-flies. The gene aniridia when faulty caused similar abnormalities in mice. On chemical analysis, the DNA structure of these two genes from fruit-fly and mouse showed a similar order of nucleotides. Flies have compound eyes and mice have camera eyes. When the mouse gene was implanted in a fly embryo with a defective eye gene, or when it was transplanted on the thorax or leg area of a normal fly embryo, the fly embryo developed compound eyes at the normal or ectopic site. Thus the same gene was similar in both the animals, but led to the development of an eye of the donee type and not the donor type.

Much of what follows below is from an article by Trevor D. Lamb in the July 2011 issue of Scientific American.

He and his associates reasoned that the development of the vertebrate camera eye dated back to over 420 million years when the jawed vertebrates arose. They looked at the retina of a lamprey (a jawless fish dating back 500 million years, but still extant) an eel like jawless fish and found it to be similar to ours. There was no known extant animal dating from 550 million years, so they looked at another jawless fish called hagfish contemporaneous with and closely related to the lamprey, and sharing an ancestor with it..The hagfish is virtually blind and its eyes may have degenerated like those of some cave fish living in total darkness, but it lives on the ocean floor. Its eyes are missing cornea, iris, lens and supporting muscles and buried under a translucent skin patch. Why does it then retain non-functioning eyes over hundreds of millions of years? 

When they looked at its retina, they found it to have only two layers, photo-receptor and output cell. It resembles the connections and functions of the pineal gland, part of the brain apparatus to regulate circadian rhythms, feeding and breeding. Even plants sense the increasing hours of daylight and know when to grow leaves and flowers without having vision. Sunflowers turn towards light and some flowers open and close petals with light or its absence. Lamprey embryo eyes resemble those of the hagfish at the surface and retina, but with maturation have three layered retina and eyes like an adult. Mammalian retina in the developing embryo begins with only two layers and over several weeks a bipolar layer develops and inserts itself between the photo-receptor and ganglion cell layers. Photo-receptors come in two types:
 
1) Ciliary which are used for non-visual functions like regulating circadian rhythms; and 2) Rhabdomeric used for visual purposes.

This is true for the compound eyes of arthropods and the camera eyes of molluscs. In vertebrates the ciliary class are used for vision.

Recent research has shown that our rhabdomeric receptors having abdicated their role in insects and molluscs, became output neurons. There was another mutation which altered the structure and properties of vertebral rhodopsin in ciliary receptors, making the light activated form more stable giving them an advantage over rhabdomeric cells in deep oceans with scarce light where our early chordate ancestors dwelled in their own niche. Rhabdomeric cells eventually lost their rhodopsin and resumed their new function of output ganglion cells. So the eye began as a few transparent light sensitive cells on the front end surface on each side. These vesicles folded inwards to form a C-shaped retina which later developed two layers, ciliary outer and rhabdomeric inner, between 550 and 500 million years ago. Then a lens forms within the open end of the C, followed by muscles to move the lens or change its shape. Then the ciliary layer replicated to form the middle bipolar layer. Then muscles formed to move the eyeball to increase the field of vision by eye movements. The Molluscs took a different route for their camera eyes and thus do not have a blind spot and an inside out retina.

Thus evolution can only tinker with what is available and sticks to a winning streak while eliminating useless and less successful variations and mutations. This is why Obama is swinging to the right to get campaign financing to be re-elected, and his strategy is to assume that the Blacks and Hispanics will vote for him because of his part ethnic background and neglect of illegal immigration and racist Republican agendas tilted entirely towards the rich. Amongst the whites the stupid ones will not vote, the foolish ones are lost to the Democratic party and will vote Republican all the way to the crematorium. He must therefore go totally with Israel to get media and monetary support and give a nod and wink to the Wall Street and country club crowd.
 
The gutting of Social Security and Medicare by the Republicans will help the old to overlook his Rube Goldberg health care plan. This will hasten doomsday for the republic rushing to embrace default and bankruptcy in the hope of permanently occupying and capturing a few oil rich kingdoms. It is reminiscent of crop disasters due to mono-culture crop or species with lack of variation going extinct by succumbing to a virulent pest or parasite resistant to pesticide or antibiotic due to over abuse. In evolution as in election politics, one has to dance with who brung ya to the ball, even if your species, majority of citizens or nation goes to hell in a hand basket, just as you have to kill more people and make more wars to get the Nobel Peace prize.   
 

18-Jun-2011
More by :  Gaurang Bhatt, MD
 
Views: 1405
 
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