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"Professor Yardley, let's assume," posited the counsel for the defense, "that I were willing to forget all the problems which have been raised with respect to the concentration issue. Do we have any way of knowing what proportion of the amino acids formed in the Archean era ocean through Strecker synthesis would be the twenty varieties of amino acid occurring in living organisms rather than the many other kinds of amino acid that are possible - some of which have been discovered in meteorites?"

"I imagine," answered the professor, "there are individuals with the talent to be able to come up with some kind of thermodynamic model that would provide a set of theoretically-driven distribution values for all the different kinds of amino acid which might be possible. However, such a model would be affected by so many variable considerations, conditions and forces, I'm not sure even our current supercomputers could keep track of the problems that would arise in this kind of model.

"One could assume less complex amino acids might tend to be somewhat disproportionately represented in relation to more complex amino acids. On the other hand, a wide array of localized thermodynamic conditions might arise which could run against these sort of tendencies.

"If temperatures in the ocean were low, say, near 0 degrees Celsius, then one would expect thermal decomposition to be low. However, some amino acids, like alanine and glycine, have far greater stability than do other amino acids, like serine.

"Consequently, stability properties would have to be factored in even if the water temperature were to remain near 0 degrees Celsius, which is unlikely. This is unlikely because within the last twenty to thirty million years there is evidence that bottom water temperatures can vary as much as 10 to 15 degrees as the Earth goes through various climatic transitions.

"What variations in water temperature, top or bottom, may have been taking place across hundreds of million years in an Archean era ocean and atmosphere are anybody's guess. Furthermore, how the decomposition tendencies of the twenty amino acids which occur in living organisms would stack up to the decomposition tendencies of all the other amino acids which are possible is another issue which would have to be factored in.

"Then, of course, one would have to work in the decomposing effect that hydrothermal vents and active volcanoes would have on amino acids which had been formed. Since we really don't have any idea of how prevalent either of these processes were during the Archean era, this introduces a further unknown into any prospective model which is being constructed.

"The effects of ultraviolet radiation in the 200 meter photic zone would have to be considered. In addition, once hydrolysis had done its magic and helped amino acids to form, then the newly-synthesized, more complex amino acids become even more vulnerable to the forces of hydrolysis than is the case for the molecules which reacted together to form them.

"Furthermore," added the Professor, "one cannot assume the only sort of synthesis reactions going on in the Archean era ocean are ones which lead to the formation of amino acids. Other, non-amino acid kinds of hydrocarbon are likely to have arisen, and this means there would have been chemical competition for available reactants, with unknown ramifications for the rate and extent of amino acid formation, both in relation to the twenty amino acids which are important to life forms, as well as in relation to the other varieties of amino acid which are not important to life forms on Earth."

"Dr. Yardley, is there," Mr. Tappin inquired, "any mechanism you know of which would have led to the specific selection of the twenty amino acids fundamental to life forms on Earth from among the myriad numbers and kinds of other amino acids that are likely to have arisen in the Archean era ocean through Strecker synthesis?"

"No," the professor answered, "I know of no plausible theory which would explain the selection process which we believe went on during the Archean era. It may well have been a stochastic process, and since we don't know enough about the factors shaping that process, we really cannot do anything but speculate why certain probability distributions might have been thermodynamically and/or kinetically favored over other probability distributions."

"Professor Yardley," continued the defense counsel, "with respect to the amino acids synthesized in the Archean era ocean through the Strecker process, would they have formed a racemic mixture - that is, a mixture consisting of roughly equal numbers of both left-handed and right-handed optical isomers of the various kinds of amino acid?"

"If our laboratory experiments are any indication, "the professor replied, "then, yes, the Archean era mixture is likely to have been racemic in character. Nevertheless, I previously have mentioned a meteorite found in the Antarctic which contained some exclusively right-handed amino acids, and this discovery does carry some potential implications for what may have occurred in the Archean era ocean."

"Are you aware, Dr. Yardley," asked the lawyer, "of any plausible account which might explain why one might end up with a set of same-handed optical isomers rather than a racemic mixture of amino acids?"

"Over the years," stated the professor, "there have been a number of proposals directed toward this problem of chirality or handedness. The only hypothesis which I have found to be plausible is one proposed back in the 1950s.

"Essentially, this hypothesis assumes that when sunlight passed through the atmosphere of the Archean era, light took on a small degree of polarization. As a result, the polarized ultraviolet component of sunlight during the Archean era may have had a preferential tendency to degrade right-handed optical isomer forms of amino acids, leaving intact the left-handed optical isomer forms which have been observed in the vast majority of Earth organisms."

"Dr. Yardley, don't most of the biologically important carbohydrate molecules tend to exhibit right-handed optical isomer preference?" Mr. Tappin inquired.

"Yes, that's right," the professor indicated.

"So, wouldn't one expect," postulated the lawyer, "that the same polarized ultraviolet component of Archean era sunlight which degraded right-handed amino acid isomers would also degrade right-handed carbohydrate isomers? Consequently, how does one account for the fact one finds right-handed carbohydrate isomers playing fundamental roles in living organisms?"

"This is a problem," Dr. Yardley admitted, "but there may have been other kinds of selection mechanisms at work in addition to the polarized ultraviolet component of Archean era sunlight."

"Does anyone," challenged the defense counsel, "know what these other selection mechanisms were that are assumed to have been operative during the Archean era?"

"Not at this point in time," answered the professor.

"Dr. Yardley, even if," the lawyer hypothesized, "one were to accept the polarized-light hypothesis as the reason why left-handed amino acids were selectively favored over right-handed amino acids as far as ultraviolet degradation is concerned, this still leaves at least two problems. First of all, the polarized- light assumption doesn't explain why DNA would possess a tendency to call for exclusively left-handed amino acids to be synthesized in the cell. Secondly, one still hasn't explained how the twenty amino acids common to life forms on Earth came to be selectively favored over the other left-handed amino acid optical isomers which would have survived being degraded by slightly polarized ultraviolet radiation. Would you agree with my assessment of the situation, Dr. Yardley?"

"As far as the second problem is concerned," stated the professor, "I would agree no fully satisfactory account presently exists for explaining why the twenty left-handed amino acid isomers were selected over other possible left-handed amino acid isomer candidates. As far as the first problem described by you is concerned, something could be said.

"Selection forces would have favored the DNA and/or RNA system which would have arisen that relied on the optical isomer form of amino acid that was available - in this case, the left-handed amino acid isomer. If a DNA and/or RNA system would have arisen which depended on the existence of a pool of right-handed amino acid isomers, then, given that polarized ultraviolet light had selectively destroyed all, or most, of these kinds of isomer, such a DNA/RNA system would not have been favored by the prevailing conditions of the Archean era world. Prebiotic conditions would have favored the DNA/RNA system which called for, or needed, left-handed amino acid isomers."

"Excuse me, Dr. Yardley, perhaps, I don't understand the situation," said Mr. Tappin. "Although your account or explanation makes sense in the context of having assumed that a left-handed-amino-acid- preferring DNA/RNA system already had arisen, your account doesn't really explain how such a left-handed-amino-acid-preferring DNA/RNA system arose in the first place ... does it?"

"No, it doesn't," the professor acknowledged.

"In fact," continued the lawyer, "wouldn't one be justified in arguing that the process of natural selection really is incapable of accounting for change over time except in a post-facto manner? By this, I mean that although natural selection can help explain why certain capabilities, once they arise, may have been selectively favored by existing conditions, nevertheless, natural selection cannot explain how such capabilities arose in the first place, can it, Professor?"

"Well," Dr. Yardley responded, "some theorists do speak in terms of the idea of 'evolutionary pressure'. In other words, they believe the collective character of any given set of conditions may, in a sense, generate a certain amount of pressure to induce the sort of changes which would be favorably selected by those conditions."

"How does this process of inducement work?" Mr. Tappin asked. "How does the physical/chemical world induce a given system to change both its structural character, as well as its way of operating, so that the system adopts a structure and set of processes which would be selectively favored by the prevailing conditions of that physical and chemical world?"

"Its a very complicated issue," replied the professor. "There is a great deal of work going on with the science of complexity, as well as chaos theory and the theory of dissipative structures which is directed toward trying to answer questions like this."

"Has anyone," inquired the lawyer, "come up with a model in any of these disciplines which has been accepted by the scientific community as a plausible account of how prevailing physical and chemical circumstances induce a system to generate structural and dynamic changes which are, capable of taking advantage of precisely the conditions which prevail in the world at a given time?"

"Not yet," responded the professor.

"Then, Dr. Yardley, would one be doing injustice to the available evidence," Mr. Tappin pressed, "if one were to say, at least at this point in time, that the notion of evolutionary pressure is a totally unproven hypothesis, however convenient and desirable an idea it may be for evolutionary theory?"

"No, I would have to say," the professor admitted, "that no injustice would be done to the available evidence."

"Consequently," summarized the defense counsel, "currently, there really is no plausible, generally-accepted explanation of how or why DNA or RNA systems arose which showed a preference for left-handed amino acid isomers as well as right-handed carbohydrate isomers. Would you agree with this statement, Dr. Yardley?"

"Yes, at the present time, what you have said is the case," agreed the professor.

"Mr. Tappin," intervened Judge Arnsberger, "I'm going to exercise some discretion at this juncture and propose that court be adjourned for lunch. Court will reconvene again at 2:00 p. m. this afternoon."

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