Bossard: What is the significance of the issue of handedness--for, say, the calculation of the probabilities Dr. Yockey gave for cyctochrome c. Does that mean we have 40 amino acids, 20 of each "hand," and we have got to worry about that?
Thaxton: 39 because glycine has no chiral carbon. But basically that's it.
Yockey: It is exactly what you say. De facto, there are more than the 20 amino acids. You do have to remember that glycine is symmetrical. And yes, it does make a big difference.
Bossard: When you were talking about the transition from one viable form to another, are you saying there do not exist viable intermediate forms or you don't know whether there exist viable intermediate forms?
Rust: We don't know.
Bossard: Simply because nobody has tried to make them?
Rust: Nobody has found any.
Bradley: I thought you implied early in your talk that if you have gene duplication then viability is less of an issue because you can do all your iterating in the gene that's not active. And therefore you don't have to have intermediate steps. Did I misunderstand your point or is that correct?
Rust: That's correct, but you still have to have a random-walk origin of the first minimal activity for a new enzyme.
Bradley: To me that's a bigger problem than the problem of viable intermediates. Right?
Mills: On one of your calculations you had a mutation rate, and of course mutation rates are not absolutely constant. There are all sorts of things, including chemical dumps, radiation, etc. that affect mutation rates. I suspect somebody will postulate that these organisms got into a radioactive area and the mutation rate went up ten-fold. To what extent will this affect your calculations?
Rust: I think there are so many orders of magnitude which are lacking in our understanding that a bit of change in mutation rates doesn't alter the conclusion much.
Thaxton: What about the idea of molecular natural selection? Chemical evolutionists often talk about a natural selection in the soup prior to the appearance of a viable living system. How do you respond to that?
Rust: Some selection in the system doesn't help as long as there is not any system.
Thaxton: You would agree with Dobzhansky and a few others who say that molecular natural selection is nonsense?
Rust: I don't quite understand.
Thaxton: Some have tried to extend the concept of natural selection in living things into the pre-living world, and have hypothesized that selection would operate at the molecular level. Dobzhansky argues that natural selection makes no sense at the molecular level, but some of the younger scientists to enter the field have felt a need for natural selection at the pre-life level and have pressed for it. Eigen, for example, has appealed to this concept of natural selection at work in the molecular soup. Any response to that?
Rust: For natural selection to work, you need some entity which is not only being selected but whose properties are maintained in some way, which means the property has to be coded in a genetic system.
Bradley: Does Eigen really talk about selection operating on molecules prior to the formation of something like a hypercycle?
Thaxton: That's my understanding. But if he doesn't, Leslie Orgel, does. Orgel wrote an article a couple of years ago in Nature, I believe, where he specifically talked about the concept of natural selection working in the soup.
Rust: Eigen does too. He talks about these quasi-species of replicating polynucleotides. But already this is a rather large system. You require at least a double-stranded RNA long enough to be stable as a duplex and having replicase associated with it, which is a rather complicated system.
Wilcox: Or it has to be replicase itself. Which means it also has to be able to recognize itself to know what it is supposed to replicate.
Thaxton: Right. It's no longer abiotic if it is replicase.
Wilcox: It seems like the minimum system that would work that way would be a stable double-stranded RNA molecule which had enzymatic activity to replicate itself and was also capable of recognizing itself and not replicating the other possible species of double-stranded RNA molecules that might be floating around. That's a fair amount of specificity already built in.
Ross: While we are on the subject of the prebiotic soup I'd just like to issue a warning. I'm predicting that NASA is going to discover extraterrestrial life in two forms. And they are going to use this as evidence that the prebiotic soup scenario by natural process works. Let me explode it in advance. Life will be found on Mars, for example, because of its proximity to the earth. There are species of life that can survive being wafted out by the solar wind for at least half a billion miles. So Mars is being bombarded by several species of life forms on a daily basis. NASA put a craft on Mars a few years ago to look for the remains of life and couldn't find it. However, they used the same craft in the Mojave Desert and they couldn't find anything there either. (Laughter) But with more sophisticated craft we shouldn't be surprised if they find something. What they find, of course, will just be remains. A liquid drop of water evaporates in one second on Mars, so it will simply be remains.
A second place where, I think, evidence of life might be found is through the radio astronomical search for extraterrestrial intelligence. Having worked in the field of radio astronomy I did a little survey, and found that about 5 percent of the observing radioastronomers were regularly seeing UFOs. Whatever your beliefs about UFOs might be, we all recognize that they're not physical phenomena. So these are two areas that might be used as evidence that the prebiotic soup really does work by natural process.
Bradley: Are you saying that any life that might be found on Mars will have been blown there from this planet?
Bradley: It could then be mistakenly identified as having started on its own.
Thaxton: If you look at something like a carbonaceous chondrite from space, some of them do contain amino acids. But they are all racemic, with both d- and l-forms, as Peter Rust brought out. Now, what if one of these chondrites actually contained a string of left-handed amino acids. They racemize over a rather short period of time. Nevertheless, would scientists be able to tell whether it came from this planet or from somewhere else? I don't think so. Presuppose that life out there is like life here. Then there would be no way to determine where it came from.
Turning it around, one of the reasons some scientists are convinced some of these meteorites reveal the existence of extraterrestrial life is that they contain amino acids, but the amino acid survey does not conform to what we know from living things here on earth. It is because of this discrepancy that leads to the conclusion that it's from outer space.
Bradley: It's also because they are recognizing the problem that the earth's atmosphere was not reducing. I was at the ISSOL [International Society for the Study of the Origin of Life] Conference in 1986 at Berkeley and there were at least two papers given by people at NASA saying all the building blocks of life came here from other parts of the universe where there is a reducing atmosphere, carried on carbonaceous chondrite meteorites. This indicates a recognition that we can no longer posit a reducing atmosphere and that therefore the Miller-Urey approach probably doesn't have any prebiotic significance, even though it's fun chemistry.
Ross: We don't have to be afraid of the Mars story because they'll find the same code there, which will prove that it originated from earth. Or else that the space of viable configurations is extremely sparsely populated.
Yockey: Of course, the proof that it's independent would be if the amino acids are d-amino acids. If they're l-amino acids, I wouldn't necessarily buy that story.
Olson: A semantic comment about the division of science into origin and operation science, or into historical and empirical science. I don't like that simply because, as a geologist, I have interest in historical science. The implication is that when you do historical science you don't use data.
Thaxton: You don't use data in historical science?
Olson: Well, that's the implication if you use historical science versus empirical science.
Thaxton: That's not what I mean by it.
Olson: To me, empirical means you get your data by sensory experiences. The geologist looking at a rock is gathering empirical data. So I for one say, Phooey. Away with historical versus empirical science.
Thaxton: Then you have a problem. If you were go to Harvard, the curriculum is divided into Science A and Science B. Science A is what I would call empirical science, and Science B is historical science.
Olson: Then I'm arguing with Harvard too. (Laughter)
Bradley: In physics and chemistry you really have an opportunity to pin things down a lot tighter.
Olson: The difference rests on reproducibility. Isn't that it?
Bradley: I think geology is inherently a lot more speculative.
Olson: Fine. Call it speculative science and non-speculative science? (Laughter)
Bradley: I think it is more speculative because you have more unavoidable limitations on the degree to which you can ascertain some things than you do in chemistry or materials science. I can easily run repetitive experiments in the lab. I can go and pull tensile bars of composite samples. In many questions geologists address, that's not possible. I know you can do some experimental work but you can't answer all your questions in that way.
Olson: I think there's a greater similarity than people are willing to acknowledge between geology and building a theory about matter at a level where you really cannot get the sensory data. I think that's very similar to building a view of the past. They both are in a sense beyond our ability to touch them. For one, the barrier is time, for the other perhaps it is size. I think the nature of the processes of thought are the same. Therefore I would rather attach the word empirical to all of science, not just one part of it.
Thaxton: Chemical evolutionists in the literature try to be careful, at least many of them do. Carl Sagan, for example, has made many contributions to this field. He will refer to what he is talking about as the story of chemical evolution, a speculative reconstruction or a scenario, as opposed to an event that is reproducible. In a reconstruction, you're trying to speculate from present conditions to what things might have been like on a primitive earth.
Coming at this literature from a physical science point of view as a chemist I had to do a lot of banging around before I began to realize what people were up to. It's a different methodology. This distinction between historical and empirical science doesn't denote different kinds of science per se but the methodological limitations within branches of science.
Meyer: I think Ed's objection about limiting the word "empirical" is well taken because even in reconstructive natural history you are reconstructing material history based on observation of the natural world. There is a difference in methodology, I agree, but I think the word empirical is a misnomer.
The methodological difference might be clarified like this. When you reconstruct the past, the question you are asking is: What happened? When you investigate phenomena in most science, the question you are asking is: How does nature work? There is a difference in focus, in emphasis. One stems from the desire to understand the laws of nature and one from the desire to understand the boundary conditions in reconstructive natural history. In fact, much of the chemical evolution literature regards the specification of the boundary conditions as the solution to the problem.
Describing the two in terms of asking two kinds of questions is a good way to understand the asymmetry of the methodology.
Wiester: As I see it, 99 percent of geology would fall into empirical science. We're talking about an extremely small area that would be historical. Empirical versus historical is just a problem distinction, not a field distinction.
Meyer: There may be some fields that do both, that are concerned with both how nature works and what were the conditions that held at a certain time in the past.
Thaxton: The way I would describe it is this. In doing historical science investigations, the scientist is switching hats all the time. There are a lot of things in geology that are subject to testable models. But when you use those testable models to extrapolate backwards to explain past events, at that point you are using a testable idea to account for something which isn't testable.
Wiester: Like what? I can't think of anything in geology, Charlie.
Thaxton: For example, you want to account for the Grand Canyon. You can study canyon formation as we observe it today. But you cannot back up time and observe the formation of the Grand Canyon itself. You can go into a lab and test the erosional process, and you can repeat your experiment as often as you like, but when you explain how a particular canyon, like the Grand Canyon, formed, that involves extrapolation into the past and so deals with events that are not repeatable. In historical science we take principles we observe today and extend them into the past to account for something which does not repeat.
Wiester: Oh. Then I withdraw my endorsement from your definition because I would disagree totally. I think we could sit down, Ed Olson and I, and show you how we could empirically establish how the Grand Canyon was formed. I think what you are really talking about, Charlie, is a methodology that is not testable by empirical processes. There you are talking about an event that occurs only once. Admittedly the origin of life occurred only once in the history of the planet earth. But I think we could take you through the process of the formation of the Grand Canyon and show you that it is 99 percent empirical science.
Thaxton: I didn't say I disagreed with that. It's that 1 percent that I'm talking about.
Meyer: One of the key issues I see is evaluating how legitimate it is to extrapolate a principle from the present into the past. For example, I read recently that many of the observed mechanisms of speciation--founder effect, genetic drift, these sorts of things--occur as a result of a depletion of a finite store of genetic information. On the other hand, the problem in macro-evolution is finding a mechanism to get an increase in the genetic store. So it strikes me as an illegitimate inference to use speciation to explain macro-evolution. Am I correct about speciation? And what do others think of this idea that we need a principle to tell us whether our extrapolations are legitimate?
Pun: I want to go back to this distinction between historical science and empirical science. I look at that from my own perspective as an experimental scientist. Every time I do an experiment I have a control. But in historical science you can't do that. I can have a control with molecular biology, molecular genetics, physical chemistry, or mechanical engineering experiments. To me the problem is how to set up your control so you can compare your data side by side.