alexis@reed.UUCP (Dimitriadis) (11/11/84)
> That was my thinking up to this morning. Now it strikes me that I have > been glossing over a pretty complex step, one which is likely to have a > lower probability than either of the ones mentioned above. That is the > step of going from something that is merely alive to a self-reproducing > (SR) cell. This, it seems to me, is the biggest step of the three. It > is one thing for the amino acids to form something that in some abstract > sense is alive, it is quite another for this thing to be an SR organism. Actually, I think it is not a low-probability event at all. Isolated DNA can self-replicate in the test tube. An organism would need to feed itself in order to be (and stay) alive, wouldn't it? That means assimilating matter from the outside. Thus it can also grow (by assimilating more than it uses up). An incerase in size could cause a primordial organism to fragment, much as a drop of oil will if shaken. If there were enough copies of the genetic material in an organism (and the restriction in the number of copies in higher organisms is no doubt artificial) then all the pieces will probably get a full complement of genetic material, QED. That is, a simple organism does not need specialized structures for replicating. Of course, it sounds so simple because DNA does self-replicate. That is probably why it is the "genetic material". The improbable event in the origination of life seems to be the establishment of a functioning genetic code: The association of the DNA with certain proteins that it "codes for", and which can "read" the code, that is, produce the proteins coded for in the DNA. (The process of transcription is enzyme-dependent, and enzymes are coded for on the DNA). The improbable event is the origination of a self-maintaining DNA-protein system. That may sound like what you had in mind to begin with, but the production of molecules peculiar to an organism is a fundamental part of being (and staying) "alive". I don't think I begged the question. I should also mention that there is a difference between an event like the origin of life and the evolution of intelligence. The origin of life seems to have been a one-step, low-probability single event. (At least, no one has come up with a multi-step mechanism for the crucial part). Intelligence, on the other hand, is a product of evolution, subject to the mechanisms of survival of the fittest etc. The one-step origination of eyeballs would be hardly less improbable than the one-step origin of intelligence. Alexis Dimitriadis alexis@reed ...
ericb@dartvax.UUCP (Eric J. Bivona) (11/13/84)
> > > That was my thinking up to this morning. Now it strikes me that I have > > been glossing over a pretty complex step, one which is likely to have a > > lower probability than either of the ones mentioned above. That is the > > step of going from something that is merely alive to a self-reproducing > > (SR) cell. This, it seems to me, is the biggest step of the three. It > > is one thing for the amino acids to form something that in some abstract > > sense is alive, it is quite another for this thing to be an SR organism. > > The improbable event in the origination of life seems to be the > establishment of a functioning genetic code: The association of the DNA > with certain proteins that it "codes for", and which can "read" the > code, that is, produce the proteins coded for in the DNA. > (The process of transcription is enzyme-dependent, and enzymes are coded > for on the DNA). > > The improbable event is the origination of a self-maintaining > DNA-protein system. That may sound like what you had in mind to begin > with, but the production of molecules peculiar to an organism is a > fundamental part of being (and staying) "alive". I don't think I begged > the question. > > Alexis Dimitriadis > alexis@reed > > ... The improbable event that Alexis mentions above is one of adding semantics to a syntactic system. This seems to me to be a *very* improbable event because the mechanism for semantics (RNA transcription) is now coded for in the DNA (excepting mitochondria). In order to start at all, some original standalone transcription system would have had to have been developed. This system (DNA & RNA transcription) would have existed in the cell without benifiting the cell until some reasonable semantic code was arrived at. This is where I would bet Nature spent three of the last four billion years [overdue and overbudget!?! :-) ] -- Eric Bivona "Once a gene sequence, always a gene sequence" UUCP: ...!{astrovax, cornell, decvax, linus}!dartvax!ericb CSNET: ericb@dartmouth ARPA: ericb%dartmouth@csnet-relay
davison@bnl.UUCP (daniel burton davison) (11/15/84)
> > That was my thinking up to this morning. Now it strikes me that I have > > been glossing over a pretty complex step, one which is likely to have a > > lower probability than either of the ones mentioned above. That is the > > step of going from something that is merely alive to a self-reproducing > > (SR) cell. This, it seems to me, is the biggest step of the three. It > > is one thing for the amino acids to form something that in some abstract > > sense is alive, it is quite another for this thing to be an SR organism. > > Actually, I think it is not a low-probability event at all. > Isolated DNA can self-replicate in the test tube. An organism would need > to feed itself in order to be (and stay) alive, wouldn't it? That means > assimilating matter from the outside. Thus it can also grow (by > assimilating more than it uses up). An incerase in size could cause a > primordial organism to fragment, much as a drop of oil will if shaken. > If there were enough copies of the genetic material in an organism > (and the restriction in the number of copies in higher organisms is no > doubt artificial) then all the pieces will probably get a full > complement of genetic material, QED. That is, a simple organism does not > need specialized structures for replicating. > > Of course, it sounds so simple because DNA does self-replicate. > That is probably why it is the "genetic material". > > The improbable event in the origination of life seems to be the > establishment of a functioning genetic code: The association of the DNA > with certain proteins that it "codes for", and which can "read" the > code, that is, produce the proteins coded for in the DNA. > (The process of transcription is enzyme-dependent, and enzymes are coded > for on the DNA). > > The improbable event is the origination of a self-maintaining > DNA-protein system. That may sound like what you had in mind to begin > with, but the production of molecules peculiar to an organism is a > fundamental part of being (and staying) "alive". I don't think I begged > the question. > > I should also mention that there is a difference between an event > like the origin of life and the evolution of intelligence. The origin of > life seems to have been a one-step, low-probability single event. (At > least, no one has come up with a multi-step mechanism for the crucial > part). Intelligence, on the other hand, is a product of evolution, > subject to the mechanisms of survival of the fittest etc. The one-step > origination of eyeballs would be hardly less improbable than the > one-step origin of intelligence. > > Alexis Dimitriadis > alexis@reed > > ... I would also suggest that those interested in the self-reproducing organism problem look at the Scentific American article by Manfried Eigen et al., April 1981. He has done some interesting work and the hypercycle model, discussed more coherently there than in other papers, has some interesting repercussions for chemical, self-reproducing "life" and evolution of such "life" (minor oxidation on) Also, re the number of copies of the genetic material being limited in higher animals, and artificial, no way. Experiments done in Drospohila melanogaster (the fruit fly) since the time of T.H. Morgan (about 1920) rather clearly demonstrate that having *extra* copies of some genes are very detrimental to the organism, i.e. it dies or cannot reproduce, which genetically is the same thing. I think it would be safe to say that there are important constraints on the number of copies of genes. especially those important in developmental regulation. (minor oxidation off) Dan Davison Department of Microbiology SUNY at Stony Brook Stony Brook, NY 11794 arpa: davison@bnl uucp: ..decvax!philabs!sbcs!bnl!davison
lab@qubix.UUCP (Q-Bick) (11/19/84)
> Dan Davison: > I would also suggest that those interested in the self-reproducing > organism problem look at the Scentific American article by Manfried > Eigen et al., April 1981. He > has done some interesting work and the hypercycle model, discussed > more coherently there than in other papers, has some interesting > repercussions for chemical, self-reproducing "life" and evolution > of such "life" If Eigen's hypotheses are the same as those in _Das Spiel_, Wilder Smith's book deals with them in depth. Aside to John Woods: What was it that AEWS said that MIT Freshlings supposedly know better of? The people at the U of Illinois Medical center (where, as a professor of pharmacology, he continually received awards for best series/course of lectures) might like to know. Then again, freshmen often think they know everything. -- The Ice Floe of Larry Bickford {amd,decwrl,sun,idi,ittvax}!qubix!lab You can't settle the issue until you've settled how to settle the issue.