To: All Msg #105, Jan3093 03:37PM Subject: Re: evidence for cumulative selection In my pre

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From: Chris Colby To: All Msg #105, Jan-30-93 03:37PM Subject: Re: evidence for cumulative selection Organization: animal -- coelomate -- deuterostome From: (Chris Colby) Message-ID: <> Newsgroups: In my previous post I tried to clearly explain the difference between natural selection (by itself) and cumulative natural selection. I then complained that I felt Johnson was scoring points in his book by using "selection" to mean both. I then said that evidence for cumulative selection came from two sources 1.) direct evidence of the components and 2.) inferences from patterns seen in living systems. (I should point out that I think the best evidence for common descent and modification with descent (which would not necessarily have to go together) comes from how traits are distributed across taxa (groups of organisms).) Finally, I asked Johnson if he would like to discuss some pertinent evidence. Since he seems to believe that the evidence from (1.) above is, in and of itself, inconclusive; I suggested we discuss evidence relating to (2.). Let's see how he responds. In article <1kbqg3$> (Phillip Johnson) writes: >A word search of the Chris Colby FAQ discloses that it, unlike >the Johnson book, does not refer to "cumulative" selection. Yep, I shouldn't have been so sloppy. The difference between my FAQ and your book is; when I fix the sliding definitions, my arguments will be better. If you clear up the terminology, your case looks worse. >It >does contain the following pertinent statements: First, >"Macroevolution is cumulative microevolution." Yes indeed it does say that. I happen to think that is true. Others in related fields to mine (some paleontologists, for ex.) think extra mechanisms such as species selection or species sorting are necessary to explain macroevolution. This, as I have pointed out in my FAQ and subsequent posts, is subject to debate. >Second, "Natural selection >is the only mechanism of adaptive evolution." Natural selection, when supplied with genetic variation by mutation or other sources, is the only accepted mechanism of adaptive evolution. Other proposed mechanisms of adaptive change (for example, inheritance of acquired characteristics) have not stood up to scientific scrutiny. Recently, adaptive (or directed) mutagenesis has been proposed to occur. I think this will qualify as a mechanism of adaptive change although I think it will be very limited in its importance compared to selection. It is too soon to tell, however, so I'm waiting before I make any sweeping changes in the FAQ -- I do mention directed mutagenesis in the "mutation" section of my FAQ. In short, if it is understood that selection needs genetic variation to work on, and genetic variation is supplied by mutation(*); I will certainly stand by the statement, "Natural selection is the only mechanism of adaptive evolution." To take our friends the moths as an example, at some time in history black moths appeared. When conditions changed selection acted and the population adapted. The adaptation could not have occurred without the mutation, but it was natural selection that increased the mean relative fitness of the population (i.e. made it adapt to the environment). (*) and gene flow and recombination Since Mr. Johnson has yet to define creative, I'm not sure if he is trying to equate adaptive with creative. Depending how creative is defined, these may or may not overlap. A reasonable definition of adaptive is a trait that increases the mean relative fitness of a population. Sometimes adaptive is defined with natural selection in the definition, along the lines of "something is adaptive if it is favored by natural selection." Clearly, that would be a poor choice of definitions in this context. On a side note, Lewontin has a (SciAm?) article in the late 70's about the problems with the term "adaptation" -- interesting, but beyond the scope of this argument. Mr. Johnson, Instead of word-searching my posts for key phrases, how about reading them for content and responding to the substance of the arguments I am presenting? In _DoT_ you claim, "My purpose is to examine the scientific evidence on its own terms,". Is this still the case? Would you like to discuss either the evidence for common descent or the evidence for modification with descent? I have recently posted a lot of information pertaining to these issues. Would you care to respond? >Phillip E. Johnson > School of Law, University of California, Berkeley CA 94720 Chris Colby --- email: --- "'My boy,' he said, 'you are descended from a long line of determined, resourceful, microscopic tadpoles--champions every one.'" --Kurt Vonnegut from "Galapagos"


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