Saturday, April 22, 2006

Natural Selection on Center Stage: Part Two

Here is another part of Princeton University President Shirley M. Tilghman's George Romanes Lecture at Oxford University on 12/1/05. The speech entitled 'Strange Bedfellows: Science, Politics and Religion' is referenced at the following URL:

Her comments are preceeded by the > symbol. Mine are not.

>"Today, however, under the banner of "intelligent design," Christian fundamentalists in the United States have launched a well-publicized assault on the theory of evolution, suggesting that the complexity and diversity of nature is not the product of random mutation and natural selection but rather of supernatural intent."

The useage of the term "Christian fundamentalists" is purposeful even if it it vague and misleading. Fundamentalist is a word used when one wishes to pejoritively paint an opponent. It generally equates to conservative Christian but has the added advantage of lumping them in the same thought category as those despised Middle Eastern fundamentalists.

If you come to subconsciously associate those who destroyed the World Trade Center with advocates of intelligent design as a result of repeated exposure to this type of lexicon then the purpose has been served. Never mind that there are Jewish and Muslim IDists or that there are Christian IDists who are not "fundamentalists." After all why let the facts get in the way of a useful prejudice.

>"Although exponents of intelligent design have been at pains to distance themselves from overtly religious interpretations of the universe, the intellectual roots of intelligent design can be traced to creationism, which holds that the natural world, including human beings in their present form, is the handiwork of a divine designer — namely, God. Biblical creationists contend that the world was created in accordance with the Book of Genesis — in six short days — while the followers of intelligent design eschew this literalism. They say that their goal is to detect empirically whether the "apparent design" in nature is genuine design, in other words, the product of an intelligent cause. They reject out of hand one of the central tenets of natural selection, namely, that biological change arises solely from selection upon random mutations over long periods of time. For those of you who are not conversant with the literature of intelligent design, the argument usually begins with Darwin himself, who said "If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down." From there, advocates such as Michael Behe, a professor of physical chemistry at Lehigh University, declare that "natural selection can only choose among systems that are already working, so the existence in nature of irreducibly complex biological systems poses a powerful challenge to Darwinian theory. We frequently observe such systems in cell organelles, in which the removal of one element would cause the whole system to cease functioning."

>"What is wrong with this view? To begin with, it reflects a fundamental misunderstanding of how evolution works."

This is a frequent criticism. If you believe natural selection does not adaquately explain the evolution of biological systems composed of dozens of interacting proteins then you must not understand how evolution works. Behe well understands the concept of natural selection. Others who share his doubts also understand the mechanisms on which natural selection is said to act. Behe's description of irreducibly complex biological systems as a challenge to Darwinian theory is apt in that biology is an empirical discipline and we do not observe the evolution of such systems. Instead we are treated to logical arguments like the one that follows.

>"Nature is the ultimate tinkerer, constantly co-opting one molecule or process for another purpose. This is spurred on by frequent duplications in the genome, which occur at random. Mutations can accumulate in the extra copy without disrupting the pre-existing function, and those that are beneficial have the potential to become fixed in the population. In other instances, entirely new functions evolve for existing proteins."

This argument says to the reader "reverse the sequence of events and see how irreducibly complex systems could have evolved." Let's do exactly that and follow the trail to a very basic biological system that is a prerequisite to the biological systems alluded to by both Behe and the author. Lactate dehydrogenase and the numerous proteins mentioned by Behe in 'Darwin's Black Box' owe their existence to biological systems that enable protein synthesis. Encoding genes are first transcribed and then translated in a process that yields encoded proteins. Numerous proteins are part of both the transcription and translation mechanisms. These proteins are themselves synthesized by the mechanisms of which they are component parts. How did natural selection produce a protein synthesis function? What would have been the selective value of any protein at a point in time when no protein synthesis mechanism existed? The translation function fits Behe's definition of an irreducibly complex biological system. Describing its existence as "a powerful challenge to Darwinian theory" is right on target. Citing mutations of gene duplications is not useful unless a means of expressing mutated genes exists.

>"My favorite example is lactate dehydrogenase, which functions as a metabolic enzyme in the liver and kidney in one context, and as one of the proteins that makes up the transparent lens of the eye in another. In the first cellular setting, the protein has a catalytic function; in the second, a structural one."

A realistic approach entails documenting the appearance of proteins forming novel functions. Irreducibly complex systems are composed of interacting proteins. Demonstrating the evolution of such systems involves detailing the sequential pathways to their constituent proteins.


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