g-rh@cca.UUCP (Richard Harter) (02/06/84)
Recently Paul Dubuc ran a transcription of a paper purporting to show that abiogenesis was an untenable concept. More recently he noted that no one had refuted it. Per his request, I will attempt to state what is wrong with the paper. Unfortunately, I did not save a copy of the paper, so I am relying on recall. Also I am not a biochemist and do not have the relevant reference material at hand, so there will be some lack of precision in my comments. The paper divides into two parts. In the first part it is argued that (a) proteins could not have formed spontaneously out of water (i.e. on the land or in the air), (b) that in liquid water they would disassociate, and (c) that they could not form in the presence of solid or gaseous water. In the second part, it is argued that the fact that all proteins are L proteins is highly improbable if proteins originally formed as a matter of chance. Amino acids come in two forms, right (D for dextro), and left (L for levro). The proteins occurring in life are made of either all L amino acids or all D acids. D type proteins are very rare. Let us dispose of the second argument first. It is a fact of biochemistry that the only way proteins can occur is either all L or all D. I do not recall off hand the reason -- it may be because that is the only way the amino acids will fit together or it may be a consequence of the mode of construction. In any case the calculations presented are irrelevant because they are based on a false assumption. The interesting question, which is not discussed, is why life is left handed rather than a mixture of left and right handed. There are two possibilities: (a) all life is descended from a single left-handed ancestor, or (b) there is some subtle reason why left handed forms are preferred. The first argument was not clear to me. I am not aware of any serious proposal that ice or steam played any part in the formation of life, so I can't judge whether the author was introducing a red herring or whether he was quoting something out of context. If he was referring to a real proposal, then I feel sure that he was misrepresenting the proposal -- the points he raised were obvious ones that any such proposal would have had to dealt with. His general point that proteins disassociate is well taken. In the absence of life organic molecules would build up in water, but they would also break down. The equilibrium point is well below the level of complexity required for life. There are some concentration mechanisms that have been pro- posed; however I am not qualified to evaluate them. Incidentally, the paper fusses about the notion that primitive Earth might have had a reducing atmosphere. As Haldane pointed out in the 20's, the oxygen in the atmosphere is produced by and maintained by plant life. Without life the atmosphere would either be reducing or neutral, depending on whether there were significant amounts of methane present. (The whole matter is currently under debate in the literature.) In short: this paper has a number of errors of logic. It has other flaws; quoted statements are misrepresented. Finally: I am not familiar with Coppredge. If this paper is a good example of the reasoning that Coppredge (sp?) uses, then Coppredge is not worth discussing. may be a consequence of the w
emjej@uokvax.UUCP (02/15/84)
#R:cca:-665200:uokvax:3800020:000:2225 uokvax!emjej Feb 11 09:35:00 1984 Re amino acids being generated in cold environments, the following quote from Dr. Jacob Bronowski (*The Ascent of Man*, p.316): "We used to think, until a few years ago, that life had to begin in those sultry, electic conditions. And then it began to occur to a few scientists that there is another set of extreme conditions which may be as powerful: that is the presence of ice. It is a strange thought; but ice has two properties which make it very attractive in the formation of simple, basic molecules. First of all, the process of freezing concentrates the material, which at the beginning of time must have been very dilute in the oceans. And secondly, it may be that the crystalline structure of ice makes it possible for molecules to line up in a way which is certainly important at every stage of life. "At any rate, Leslie Orgel did a number of elegant experiments of which I will describe the simplest. He took some of the basic constituents which are sure to have been present in the atmosphere of the earth at any early time: hydrogen cyanide is one, ammonia is another. He made a dilute solution of them in water, and then froze the solution over a period of several days. As a result, the concentrated material is pushed into a sort of tiny iceberg at the top, and there the presence of a small amount of colour reveals that organic molecules have been formed. Some amino acids, no doubt; but, most important, Orgel found that he had formed one of the four fundamental constituents in the genetic alphabet which directs all life. He had made adenine, one of the four bases in DNA..." The creationists' bogos "proofs" that abiogenesis is so improbable as to not be worth considering typically cheat their way to plausibility by confusing probability with conditional probability. To give an analogy: find a barn wall, and throw a dart at it. Now, if someone were to come along and throw another dart at the barn wall, it would be extremely unlikely that they would hit the *exact* spot you hit first (so if I were a creationist, I would say that clearly the hand of God directed your dart to hit where it did); on the other hand, he is almost certain to hit somewhere on the barn wall... James Jones