reiser@pmafire.inel.gov (Steve Reiser) (01/04/91)
In tests reported in a 1989 issue of "Noetic Science Review", it was found that a bacteria exposed to a virus which is fatal to the bacteria had a 70% survival rate due to a genetic double mutation which required mutation "A" to occur before mutation "B" at specific locations on the DNA. The mutations protected the bacteria from the virus. The article suggested that much of evolution may have been non-random and selective mutations occur allowing species to advance at an infinitely faster rate than would be probable by random genetic mutation. This finding suggests that evolution is harder to explain away than it had been when statistical probabilities of evolution creating man was used to suggest that it was necessary for a god to intervene. Steve -- Steve Reiser (reiser@pmafire.UUCP or ...!uunet!pmafire!reiser)
hes@ccvr1.ncsu.edu (Henry E. Schaffer) (01/05/91)
In article <1991Jan03.201603.25448@pmafire.inel.gov> reiser@pmafire.inel.gov (Steve Reiser) writes: > Who said that evolution was random? >In tests reported in a 1989 issue of "Noetic Science Review", it was I'm not familiar with this journal, and my university's library does not have it. Could you tell us more about it? >found that a bacteria exposed to a virus which is fatal to the bacteria >had a 70% survival rate due to a genetic double mutation which required ^^^^^^^^^^^^^^^^^ a) That doesn't sound "fatal" to me if 70% survive. b) I don't think this is what they said (or what happened) - a much more reasonable situation would be that 70% of the "cultures" survived. I.e., they had a series of test tubes, each of which had a large number of bacteria (maybe 10**10) from a strain which is killed by the virus. The virus was added to each of the test tubes, and killed all the bacteria in 30% of the test tubes. In 70% of the test tubes, at least one bacterium survived. (The surviving bacterium was able to grow back to make a perceptible amount of bacteria.) They were able to show that the mechanism of resistance to the virus was a double mutation. (end of what a reasonable scenario would be) >mutation "A" to occur before mutation "B" at specific locations on the >DNA. The mutations protected the bacteria from the virus. This kind of situation is *very* common in the study of bacteria. Mutations happen all the time, all sorts of mutations. But each particular mutation, or set of mutations, is very rare. Still when put in a "selective" situation (i.e., one in which only a particular genotype survives) then we can find the presence of even a rare mutation. The BIG question is whether the selective situation uncovered a pre-existing "good" mutation ("good" because it lets the bearer survive in this particular situation) or whether the mutation occurred afterwards to "help" the individual adapt to the selective situation. This was an important question in biology, and it wasn't settled until the 1940's. The "fluctuation test" of Luria and Delbruck (S.E. Luria and M. Delbruck, Genetics 28, 491, 1943) is considered to have settled the question, but probably took until around 1950 before it was widely understood and accepted. (Some of the delay was probably due to world events of that time.) They showed that these adaptive mutations existed before the selective event and the selective event just exposed them to view (versus the alternative that the adaptive mutations occurred in response to the selective event.) Therefore the mutations are random, but the "evolution" is in response to selective conditions and therefore is adaptive. >The article suggested that much of evolution may have been non-random fine >and selective mutations occur allowing species to advance at an infinitely but this goes against what is known in biology - in fact, people have been trying hard to figure out ways to cause particular mutations to occur ("directed mutagenesis") and so far there has been little progress. >faster rate than would be probable by random genetic mutation. > >This finding suggests that evolution is harder to explain away than it >had been when statistical probabilities of evolution creating man was >used to suggest that it was necessary for a god to intervene. I don't think that evolution can be "explained away" even without this article. All of the "statistical probabilities of evolution creating man" arguments I have personally seen have been bogus. (They typically attempt to calculate the probability that in one cell division an amoeba mutates to a human cell, and calculate that in ways which systematically underestimate the probabilities of each of the factors involved.) The creationists have a religious basis for wanting to deny evolution, and have a large variety of arguments "explaining away" evolution, but that's a different issue. --henry schaffer n c state univ
toms@fcs260c2.ncifcrf.gov (Tom Schneider) (01/05/91)
In article <1991Jan4.160016.16574@ncsuvx.ncsu.edu> hes@ccvr1.ncsu.edu (Henry E. Schaffer) writes: (ie, >) >In article <1991Jan03.201603.25448@pmafire.inel.gov> reiser@pmafire.inel.gov (Steve Reiser) writes: (ie, >>) >The BIG question is whether the selective situation uncovered a >pre-existing "good" mutation ("good" because it lets the bearer >survive in this particular situation) or whether the mutation occurred >afterwards to "help" the individual adapt to the selective situation. > > This was an important question in biology, and it wasn't settled >until the 1940's. The "fluctuation test" of Luria and Delbruck >(S.E. Luria and M. Delbruck, Genetics 28, 491, 1943) is considered >to have settled the question, but probably took until around 1950 >before it was widely understood and accepted. (Some of the delay >was probably due to world events of that time.) They showed that >these adaptive mutations existed before the selective event and >the selective event just exposed them to view (versus the alternative >that the adaptive mutations occurred in response to the selective >event.) > > Therefore the mutations are random, but the "evolution" is in >response to selective conditions and therefore is adaptive. I think that the article refered to by the first poster may have been a spinoff of the recent debate about mutation under growth inhibitory conditions. Some people claim that mutations appear to be directed to the particular genes where a mutation would help the organism. This APPEARS to run against the original Luria Delbruck experiments! I think that the original paper on the topic was: @article{Cairns1988, author = "J. Cairns and J. Overbaugh and S. Miller", title = "The origin of mutants", journal = "Nature", volume = "335", pages = "142-145", year = "1988"} So far as I know this has NOT been resolved! >>and selective mutations occur allowing species to advance at an infinitely >>faster rate than would be probable by random genetic mutation. The original paper or the first poster has made a mistake: "infinitely faster" can't be right! > but this goes against what is known in biology - in fact, people >have been trying hard to figure out ways to cause particular mutations >to occur ("directed mutagenesis") and so far there has been little >progress. Nope, sorry Henry, but "directed mutagenesis" works just fine. One can make any changes one wants to a piece of DNA. In some species one can put the change back into the chromosome too. There are many ways to do it and one can confirm the results with well established sequencing techniques. >>This finding suggests that evolution is harder to explain away than it >>had been when statistical probabilities of evolution creating man was >>used to suggest that it was necessary for a god to intervene. This makes no sense to me. There is no need to 'explain away' evolution. Mutations are observed in the lab every day. The sequence data indicates common origins and variations. The evidence for this is overwhelming if the original poster would only go read a bit! > I don't think that evolution can be "explained away" even without >this article. All of the "statistical probabilities of evolution >creating man" arguments I have personally seen have been bogus. Right. And anyone who wants to argue should read this book first: @book{Dawkins1986, author = "R. Dawkins", title = "The Blind Watchmaker", publisher = "W. W. Norton \& Co.", address = "New York", year = "1986"} >(They typically attempt to calculate the probability that in one >cell division an amoeba mutates to a human cell, and calculate that >in ways which systematically underestimate the probabilities of >each of the factors involved.) The creationists have a religious >basis for wanting to deny evolution, and have a large variety of >arguments "explaining away" evolution, but that's a different issue. But, despite overwhelming evidence, not resolved! >--henry schaffer n c state univ Tom Schneider National Cancer Institute Laboratory of Mathematical Biology Frederick, Maryland 21702-1201 toms@ncifcrf.gov