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Feathers of a bird
Are you not amazed at what millions of years of evolution can do? You could spend your lifetime studying the structures and functions of bird feathers - all crafted, according to evolution theory, by the marvelous sifting powers of natural selection when put to work on the untold billions of random mutations allegedly undergone by feather-forming genes over the eons.
Well, I hope you haven't bought into this ultimate fairytale of all fairytales. The natural world is just way too complex, too sophisticated, too ingenious to have arisen "by natural means". How can an intelligent person possibly believe that the staggering variations on the theme of feather color and pattern, for instance, arose by accident? (Yes, yes, I know Richard Dawkins would get into a lather at the attribution of "accidentality" to evolution, but standard evolution theory has always acknowledged its contingency.) Feather color has intrigued, baffled, and excited scientists for decades and decades. Researchers have enjoyed many Eureka moments and look forward to many more. The topic is just way too vast for any mortal to fully grasp. Since color is a function of light, a big part of the challenge in understanding feather color stems from the more fundamental question, what is light? As Hilda Simon puts it,
Despite the fact that we have learned much about the nature of light, a satisfactory answer to the question, What is light? has not yet been found, and it remains the enfant terrible of science. During the past three hundred years, eminent scientists from many countries have advanced a number of often sharply differing theories on the nature of light. Color plays an important part in all these theories. 1
Feathers exhibit a staggering array of color schemes and of techniques for producing the schemes. All the various techniques consist of variations on the two fundamental methods of imparting color to an object - chemical and structural. The light that comes from the sun contains all the "colors of the rainbow"; an object looks a particular color because only some of those possible colors reach our eyes when the light bounces off that object. "Chemical color" is the result of the absorption of some wavelengths (colors) of the sun's light by chemicals (pigments) within the object. The mix of wavelengths that are not absorbed but are instead reflected imparts a particular color to the object. The color does not depend on the angle of the object's surface relative to our eyes. Many feathers depend for their color on pigments contained within the feathers. Variety is one of the hallmarks of almost all of creation's themes, so it should come as no surprise that a broad spectrum of chemicals is involved in the making of feather colors. Although all blacks, browns and grays in the animal world are produced by a group of pigments known as melanins, many other pigments play a role, too. Although many of the pigments have already been identified by scientists, work continues apace. A recent report tells us that,
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For more than a century, biochemists have known that parrots use an unusual set of pigments to produce their rainbow of plumage colors, but their biochemical identity has remained elusive. 2
Researchers have now found a suite of "five molecules, called polyenal lipochromes (or psittacofulvins), that color parrot plumage red in all of the species studied. It is a unique pigment found nowhere else in the world. We are fascinated at how parrots are able to do this". We should be, too; trouble is, we would have to hit the books hard to get up to speed. But eternity is a long time; one day believers will understand all such things. Bottom line; even if mutations and natural selection had eternity to work their alleged magic, they would never succeed in synthesizing such molecules.
Once again, variety steps in. Some birds have to get the pigments fully-formed from the food they eat. For a long time zoo-keepers were distressed by the fading plumage of many captive birds, such as flamingos. The problem was solved when William Conway discovered that chopped shrimp added to the diet fixed the problem. (Flamingoes must have spent millions of years learning the trick of getting the pigments through the digestion processed unharmed.) Bright red macaws, by contrast, synthesize the psittacofulvins at the site of feather formation themselves. Many more millions of years!
By contrast to chemical color, "structural color" is due to the physical makeup of the object's surface. None of the light is absorbed; the surface microstructure sends some wavelengths off in one direction and other wavelengths in other directions. Exactly what you see varies with the angle of the surface object relative to your eyes. Many forms of structural color produce what we call iridescence, that metallic sheen we associate with flashy cars and gaudy beetles. When it comes to birds, well, the sky is the limit as to the species that exhibit some iridescence. The classical case would have to be the peacock. What clever birdies to figure out not only how to grow shapely feathers and erect them at the appropriate time but to also sculpt a remarkable suite of microstructural patterns on the feather's surfaces capable of producing the gorgeous patterns we and the peahens see. All blues in birds, it would seem, are a result of structure. Not only do bright, flashy birds such as kingfishers produce structural colors, so do more mono-colored, dark birds such as crows, ravens, grackles, and starlings.
Only a master sculptor and consummate scientist could sculpt the enormous variety of physical microstructures displayed by feathers.3 Furthermore, different parts of a feather can produce color by different methods; barbs produce non-iridescent colors, barbules iridescent ones.4 Now that takes planning. And there's even more; some surfaces with more than one very thin layer can combine both forms of color production, with one layer responsible for chemical color and the other for structural color effects. Evolution? Pull the other wing.
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