Panel Discussion, continued...
SCOTT: But I think it's fascinating that so many people think that life is an inherently unlikely thing to have occurred on the early Earth. But the material we've heard today suggests that it is virtually inevitable and probably was a multiple, an occurrence that happened multiple times. Rich?
MULLER: I wouldn't agree with that at all. I didn't hear anything to that and this is a question that's a great interest to me because I work in astrophysics. I always wonder about extraterrestrial life and how likely it is. Because most of my friends say it's very, very probable and therefore we should be looking for it, I may be perverse taking the other point of view and saying well, I'd like to fill in the details of that argument. There's something called the Drake Equation in which you put in thirty well-known terms and four terms that are completely unknown and you come up with a number that's completely unknown in my mind. I didn't hear anything today that said to me that life was inevitable or that the probability, that if we did Earth over again, that we'd get life again is anything great. I don't know about that. I didn't hear anything today that convinced me that life was inevitable.
Getting back to your first question about what is life, I want to get a physicist's perspective on that. There are things that reproduce themselves by taking in energy or giving it off, in some cases. One example is a crystal which grows -- a little sugar, you saturate it and it grows. We don't call that life. Fire, light a match and it spreads, it reproduces. You don't call that life. I think a characteristic of life from the point of view of a physicist is that organism which reproduces itself has an astounding degree of complexity. If that complexity isn't present, then we don't call it life, we call it something else. So we have an organism that has a certain minimum complexity, something that makes it so unlikely that it's any sort of spontaneous random change and then manages to reproduce itself. That's miraculous and when something is miraculous we call it life.
Q: Isn't that selectively DNA?
MULLER: Yes, well, it is, but there are organisms that don't use DNA and they're still life.
SCOTT: I think most biologists would define, a minimal definition of life. Obviously your textbooks are full of definitions of life, "it moves, etc". I think a biologist would minimally define life as something that reproduces, but as Rich pointed out, so does fire. But also that has the capacity for change. At that point, what we're almost doing is defining life as something that can evolve. This makes a lot of sense, because when you look at what we know of the history of life, which is partly what we've been talking about today, we see that change through time, this set with modification, has characterized life from the very beginning. As Stan was saying, the first reproducing molecules might have eaten up all of the resources that they could through the fermentation process. There would have been natural selection upon those organizations that were capable of generating their own energy. Well, one biological definition is something that can reproduce and upon which natural selection can operate. A possibility.
AWRAMIK: I want to just throw in something. Why I was really struggling with defining life is that both Rich and Eugenie were using some of the terms and phraseology, of an organism. It wasn't a totally descriptive term. We're stuck using some of the attributes, like I said reproduction. We're using some of the attributes and terms to define life.
LIPPS: My historic organism kind of assumed that life would be localized. And yet, someday after computers have taken over the world and carbon based life has been destroyed, the kind of life that exists may not be localized. The ethernet might be one form of life.
SCOTT: Let's go to the audience.