Monday, November 06, 2006

Evolution of Complex Organs

One of the most common attacks on evolution is to assert that complex organs such as the eye could not evolve since they only work when all parts are present. National Geographic, obviously intent on showing that this claim is false, has published an article in the November 2006 issue detailing the wealth of evidence for how such organs evolve. For the Internet version of the article, see http://www7.nationalgeographic.com/ngm/0611/feature4/.

The jist of the article is that marvels such as the eye, the arm, feathers, and flowers are, in fact, built up from primative beginnings through minute changes that over millions of years add up to the organ in question. Furthermore, the same genes are used in different organisms to develop different forms of an organ or limb. For example, "Insects and humans use the same genes to tell cells in their embryos to turn into photoreceptors. And both kinds of photorecptors snag light with molecules known as opsins" [p. 126]. This is as would be expected if eyes of insects and humans evolved from some very early common ancestor which evolved a simple way to detect light. Later elements like the lens of a more advanced eye evolved out of a transparent protein called crystallins, which existed well before the eye used them to build a lense.

This puts the lie to another accusation made against evolution, that only microevolution has been demonstrated (slight changes within a given species, such as foxes with different colored fur in the arctic and the temperate zones), not macroevolution (the evolution of new species). Small changes, over a long enough time, can lead to major differences in the way a set of genes shapes the organism. It is not a quirk of some intelligent designer that all mammals have virtually the exact same skeleton, even though the bones are often put to very different uses: whale "hands" are fin for swimming, bat "hands" form wings, and human hands can create complex tools. The same goes for feathers, which evolved from scales, serving various uses during the intermediate period between scales and flight feathers.

Despite all this evidence, the same false accusations are made over and over and over again by proponants of creationism and intelligent design. Yet they claim it is the scientists who are dishonest, giving the public a false sense of certainty regarding evolution. [For one example, see: http://www.discovery.org/scripts/viewDB/filesDB-download.php?id=118 .]

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