Not all evolution is Darwinian.
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Many non scientists and scientists alike have the idea that all evolution must have involved natural selection, the mechanism of biological evolution proposed by Darwin. But we know that this is not true. After all, astronomers talk about the evolution of stars and galaxies. This is not Darwinian in the sense that there is no natural selection for stars of certain genetic makeups: the concept makes no sense for stars. Yet stars and galaxies do evolve in the general sense of change through time. At more familiar levels of organization, the geology of our planet certainly evolves through time. We can, for instance, measure the rate at which various continental plates are moving with respect to each other and the rate at which sea bottom is being taken up at the mid Atlantic ridge.
Ecosystems and biological communities evolve both across and within historical times. This type of change does not involve Darwinian evolution except in the long term where species coevolve with respect to each other. At the level of microevolution: this is not all Darwinian either. Microevolution for instance, for species with relatively few members, involves a process called genetic drift in which certain alleles go extinct in a communities population just by chance in much the same way a coin tossed ten time might come up all heads.
Recently there has been a lot of attention paid to how life might have arisen, and here we seem to have a problem. The simplest cell seems much too complex to have arisen by evolution. Thus some people, including scientists who should know better, have postulated that cells were in someway designed, or in the case of Fred Hoyle, that the cells we see on this planet did not arise here but some how migrated here from outer space. So far the evidence for Hoyle's idea is scant, and evidence for the design idea rests on negative evidence. Since we cannot yet come up with a rigorous explanation for how life might have arisen, therefore creation by design is the only hypothesis left: the only hypothesis that explains the complexity of even the simplest cell.
Is this true though? First, a basic assumption of science is that the universe can be understood rationally. How does the idea of design fit into science? It does not for once you postulate design by something then you set up the task for science of explaining what this something is in rational terms. Thus so called "Creation Science" is an oxymoron because the concept of design cannot be reconciled with the idea of rationally explainable universe. I suppose one could say that the cell is so complex that science can go no farther and draw a line between what is explainable by scientific terms(bacteria and above) and what is outside rational explanation. Personally, I don't buy that tactic and most other biologists probably don't either because the question still remains: how did the first cells develop? Plus, this one question subsumes a whole range of subtle biochemical questions such as: how did the genetic system used by cells today and the mechanism of protein synthesis come about, and how did complex metabolic pathways such as the Kreb's cycle evolve? What are the origins of biological order?
Recently Stuart Kauffman(The Origins of Order, Stuart A. Kauffman, Oxford University Press, 1993) has attempted to attack just these sorts of problems. Dr. Kauffman is an exponent of complexity theory which attempts to understand the evolution and behavior of complex systems in mathematical terms. Certainly even the simplest cells are complex systems. Dr, Kauffman notes several things that are of particular interest to biologists. First, systems of randomly connected components quite commonly, and quite contrary to our intuitions, spontaneously arrange themselves in a complex order. This somewhat analogous to what biochemists and biologists know as self assembly. Next he observes that if you have a small polypeptides of different types the probability, is contrary to what one might expect, quite high that they will catalyze the synthesis of additional polypeptides and you will get a closed loop where one polypeptide is likely arise indirectly be catalyzing its own synthesis. Thus the standard probability arguments about how easy it is to get a functional enzyme from a soup of amino acids does not apply and our intuitions about how easy it is for complex systems, such as cells may very well be wrong. Kauffman makes analogous arguments for how easy it is to get self replicating molecules such as DNA or more likely some other nucleic acid like polymer.
Then Kauffman says something that to me was quite startling: namely that once you have a metabolic pathway, or set of chemical reactions isolated within a phospholipid type membrane, then this metabolic pathway may itself be self replicating. In other words self replication need not involve genes. This an intriguing concept because normally we think of evolution of biological systems as involving genes. Here though we have the possibility of protein synthesis and metabolic pathways without genes! Obviously there are a whole bunch of unanswered questions. But what Kauffman has done is opened up the range of processes that can give rise to complexity. Darwinian evolution is not necessary for this. Neither though is invoking design. The point is not that science will be able to explain exactly how life arose, but rather that it may very well be possible to come up with one or more rational explanations which make sense in terms of the physical laws by which the rest of the universe seems to operate.
Kauffman's book is full of wonderful concepts related to complexity and the evolution of life. The mathematics basically involves combinatorics and is at times difficult to follow. But for those biologists interested in how life might have come about this book is necessary reading and a welcome rebuttal to those folks who throw up their hands at the idea of ever understanding how life could have arisen.
© Paul Decelles 4/6/99, 9/5/99
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PGD 4/16/99 revised 6/1/99.
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