Friday, April 21, 2006

Natural Selection on Center Stage: Part One

On 12\1\05 Shirley M. Tilghman, President of Princeton University, delivered the George Romanes Lecture at Oxford University. The speech entitled 'Strange Bedfellows: Science, Politics and Religion' is referenced at the following URL:

A part of the speech concerning natural selection and intelligent design is noted here and comments are directed at it. From the speech:

>"If cosmologists are deciphering the origins of the universe and our solar system in unprecedented ways, biologists are making enormous strides, thanks to the technology that was developed during the Human Genome Project, toward unlocking the origins of life on Earth. Yet here, too, science and politics have found themselves at loggerheads. It is impossible to ignore the increasing assertiveness of elements within American society who have challenged the validity of Darwin's theory of natural selection and have lobbied for an alternative explanation, which they term "intelligent design," to be taught in public schools alongside the principles of evolution. This is deeply disturbing, for the theory of natural selection is one of the two pillars, along with Mendel's laws of inheritance, on which all of modern biology is built."

Natural selection is indeed a theoretical pillar of evolution. Initially invoked by Darwin as a logical argument, it remains primarily a logical rather than an empirical device. Tilghman's use of the term natural selection infers that intelligent causality and natural selection are mutually exclusive concepts. But are they?

Examples of natural selection have focused largely on adaptations found in unicellular organisms and insects; organisms with high rates of reproduction. Of course in all organisms lethal genetic changes are eliminated from the gene pool as well. What we do not observe is the generation of new biological systems consisting of a large complex of interacting proteins. If natural selection accounts for the existence of such systems then what is the evidence? Citing the selective value of a protein or complex of proteins is akin to stating there is biological utility in their function. Parallel functions can be identified in enzymes found throughout the living world. Identical substrates can be catalyzed by enzymes found in very different organisms. Given that the primary structure of such enzymes is very similar a case for common descent is made. Whether attributed to common descent or common principles of design an identical substrate can dictate the constituent residues of an active site. Explaining that nearly identical enzymes of different species associate with metal ion cofactors with invarient atomic structures like zinc or iron tells us of an affinity between them and shared amino acids. That affinity is a cause of the enzyme similarity. A cause linked to natural history entails a secondary inference which is intrinsically less reliable as a causal factor. More from Shirley M. Tilghman:

>"It is virtually impossible to conduct biological research and not be struck by the power of Darwin's theory of natural selection to shed light on the problem at hand. Time and again in the course of my career, I have encountered a mysterious finding that was explained by viewing it through the lens of evolutionary biology. The power of the theory of natural selection to illuminate natural phenomena, as well as its remarkable resilience to experimental challenge over almost 150 years, has led to its overwhelming acceptance by the scientific community."

Too bad we were not treated to an example of an explained mysterious finding. There are many unmysterious biochemical reactions that do not lend themselves to natural selection explanations devoid of an unacceptable level of speculation. Pyruvate is converted to acetyl CoA by what is known as the pyruvate dehydrogenase complex consisting of three distinct enzymes each catalyzing a part of an overall reaction. Regulatory enzymes are also involved in the process. There would have been a point in time when none of the enzymes existed as well as none of their encoding genes. There is no question about the biological utility of the enzymes to the conversion. It is equally clear that the enzymes operate in concert to effect the conversion. What does natural selection tell us about the evolution of this complex? No doubt imaginative minds can conjure up an evolutionary pathway but like other putative precursor pathways it would raise more questions than it answers. As we trace our steps backward it becomes increasingly apparent that the theoretical underpinnings of selection concepts becomes more vague and predictions less reliable as natural selection faces the task of explaining the genetic ediface on which the mechanism depends. Natural selection becomes less reliable even as a logical indicator when the selection criteria needed to generate a minimal functional genome is not even known.

The author links the utility of natural selection to research and in doing so comes squarely in conflict with the views of Professor Philip Skell. His comment and the referenced URL for the article follow:

"Last year, Dr. Philip Skell, Emeritus Evan Pugh Professor at Pennsylvania State University and a member of the U. S. National Academy of Sciences, wrote in The Scientist that he"

"examined the outstanding biodiscoveries of the past century: the discovery of the double helix; the characterization of the ribosome; the mapping of genomes; research on medications and drug reactions; improvements in food production and sanitation; the development of new surgeries; and others. I even queried biologists working in areas where one would expect the Darwinian paradigm to have most benefited research, such as the emergence of resistance to antibiotics and pesticides. Here, as elsewhere, I found that Darwin's theory had provided no discernible guidance, but was brought in, after the breakthroughs, as an interesting narrative gloss."

That's my take as well. Natural selection is brought in to explain results rather than as a guide toward them.


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