I'm curious about where the pool is divided on this sensitive issue, so I decided to add a little air to the fire and see where it goes.
My position, as an acolyte of the science of biology, is that the best explanation for the origin of species lies within the vast pools of evidence that have been accumulated over hundreds of years in support of evolution. On the other hand, Biblical Creationism is but a fiction conceived in the minds of the disillusioned. Proponents of Creationism carefully beguile their victims with equivocal language, pseudoscientific sophism, and occassionally outright lies, in order to "prove" a "theory" which makes no testable predictions and lacks any sufficent mechanism by which it operates.
For example, we'll use the claim that mutations are harmful or that no beneficial mutation has ever been observed. While it is true that most virulent human diseases are caused by genetic defects (downs syndrome, sickle cell anemia, hemophilia, and progeria, to name a few), most mutations are actually neutral. That is, neither beneficial nor deleterious. To counter the claim that no beneficial mutation has ever been observed, let's go back to the mid-1970s at the University of Rochester where Professor Barry Hall is conducting an experiment with special strains of E. coli. A typical nutrient of bacteria is lactose, so Hall decided to remove the lacZ gene, responsible for the metabolization of the milk sugar substance. Hall placed one strain in an environment rich in lactose with little nutrient to survive on, and the other strain was placed in an environment with no lactose. The former recovered its ability to metabolize lactose over the course of a few days, with two mutations to preexisting genes along a different operon in the genome from the original. The first mutation produced a beta-galactosidase enzyme (34% homologous to its predecessor), tasked with breaking down lactose via a process of hydrolysis into the two monosaccharides glucose and galactose. This new enzyme was dubbed the ebg, or evolved b-galactosidase enzyme. The second mutation altered the control region, or repressor protein (25% homologous), so that the enzyme may be expressed in the presence of glucose. The second strain displayed no such progress.
In Chapter 5 of the book Finding Darwin's God (HarperCollins, 1999), Professor of Biology Kenneth Miller at Brown University adds, "That would have been impressive enough, but Hall's clever germs didn't stop there. When he selected them further to grow on another sugar (lactulose), he obtained a second series of mutants with a new enzyme that accidentally (in a sense) produced allolactose, the very same chemical signal that is normally used to switch on all of the lac genes. This important development meant that now the cells could switch on synthesis of a cell membrane protein, the lac permease, that speeds the entry of lactose into the cell."
Some would consider Hall's experiments early evidence in support of the adaptive mutagensis hypothesis. It states that not all mutations are random and a cell can yield a necessary mutation on its own, almost as if it chose to. I'm not certain I'm ready to accept that just yet, however considering this is only my opinion I could be wrong. It is important to remind ourselves that evolution is not guided by conscious design, it operates without regard to the longevity of the organism it affects. The results of Hall's work are not surprising at all, even when one considers the neutrality of most mutations. John Cairns, et al. (1988) demonstrated with E. coli that stress on an organism, created by a significant threat of survival, increases the rate of mutation. However, this should and does not make "good" or "bad" mutations any more or less likely to occur, you are merely increasing the frequency of mutations period. The disposition of mutations remain proportionate to the mutation rate.
We are now faced with the issue of whether this method of metabolization fits the criteria of something that is irreducibly complex. For those who are unfamiliar with this concept, a biological system that requires multiple parts to emerge nearly concurrently in order to properly function is irreducibly complex. Professor Michael Behe of Lehigh University, an established proponent of Intelligent Design, is credited with inventing this idea. He claims, "An irreducibly complex biological system, if there is such a thing, would be a powerful challenge to Darwinian evolution." Unfortunately for Professor Behe, the challenge was not as great as he imagined and the amount of literature responding to that claim is practically insurmountable. This particular example is not exempt from that challenge, both mutations were absolutely necessary or else the system would simply not function. Behe criticized the multipart system in response to Miller in an essay written for the Discovery Institute. He quoted Hall as saying, "All of the other functions for lactose metabolism, including lactose permease and the pathways for metabolism of glucose and galactose, the products of lactose hydrolysis, remain intact, thus re-acquisition of lactose utilization requires only the evolution of a new B-galactosidase function." Behe continued: "Thus, contrary to Miller's own criterion for 'a true acid test,' a multipart system was not 'wiped out' -- only one component of a multipart system was deleted." The misunderstanding here is clear, and partly semantical. Behe is not convinced an irreducibly complex biochemical system can evolve, and so he misses the point made by Miller. In fact, Miller had also said that all Hall had done was remove one gene, but it wiped out a multipart system in the sense that lactose can not hydrolyze in the absence of this enzyme. Behe also found it disappointing that the new ebg arised from a different, relatively unrelated operon, however he is again missing the point that that is part of the process of evolution. If you would like a more in-depth analysis of Behe's criticism, you may read Miller's own rebuttal on the web at http://biocrs.biomed.brown.edu/Darwin/DI/AcidTest.html. It is easier for me to simply supply you with the link rather than extend the post to an intolerable length by simply rehashing what has already been said by Professor Miller.
It is in conclusion that I ask you treat this issue fairly and maturely. All too often, this controversial topic ends up spiraling off the deep end into petty disputes and elementary insults. It is often the result when two seemingly intelligent people having a nice debate realize they can not coax the other with simple reason. So rather than do the reasonable thing and agree to disagree, they turn to the next best thing: the most unreasonable and childish move they can conceive of. Furthermore, it is imperative we remain on topic. Continuing this line of discussion, and then suddenly asking how the Big Bang started is not the proper way to handle a debate concerning a topic of biology. If you wish to argue Young Earth Creationism, it is your prerogative to start a new thread for that express purpose. This thread is for debating the merits of evolution, and I will not respond to nongermane assertions. This does not mean the line of discussion is limited to Hall's experiments alone, otherwise the thread would have been named to something more specific. I am open to discussion on other fronts of the evolution debate as well, and I have faith that we will have no trouble keeping posts relevant to the topic. If I sound condescending, my apologies, that was not my intent. I look forward to the replies.
1 Drake, J.W. et al (1998) Rates of Spontaneous Mutation. Genetics 148:1667-1686. [Link]
2 Further reading:
3 Colby, C., Williams, S.M. (1995) The Effect of Adaptive Mutagenesis on Genetic Variation at a Linked, Neutral Locus. Genetics 140:1129-1136. [Link] (Adobe® Acrobat® required to view reprint in PDF format)
- Hall, B.G. (1982) Evolution on a Petri Dish. The evolved b-galactosidase system as a model for studying acquisitive evolution in the laboratory. Evolutionary Biology 15:85-150.
- Hall, B.G. (1983) Evolution of new metabolic functions in laboratory organisms, in Evolution of Genes and Proteins. Evolution of genes and proteins, eds. M. Nei, and R. K. Koehn. (Sunderland, MA: Sinauer Associates Inc).
4 Behe, M.J. (1996) Darwin's Black Box: The Biochemical Challenge to Evolution. Free Press, p.39.
5 See also: Robinson, K. (1996) Darwin's Black Box: Irreducible Complexity or Irreproducible Irreducibility? Talk.Origins. [Link]
6 Behe, M.J. (2000) "A True Acid Test": Response To Ken Miller. Discovery Institute. [Link]
7 Hall, B.G. (1999) Experimental evolution of ebg enzyme provides clues about the evolution of catalysis and to evolutionary potential. FEMS Microbiology Letters 174:1-8.