The necessity for mutation is considered non-essential by Scott-Monkey Trials-Hatfield, who suggested that I peruse the PNAS files for direct information. The PNAS files do hold a lot of papers. A search for "human plasmids" turned up over 54,000 papers. Clearly a tough job to peruse. I will go back to PNAS as time permits. However, I have three more sources to quote on the subject of whether mutation is necessary for enabling adaptation by selection to move outside the genome.
First, I will quote from "The Making of the Fittest"; S.Carroll; 2006, Norton & Co, Ch 2: "The Everyday Math of Evolution: Chance, Selection, and Time", pg 57:
"The source of all variey is mutation." And, "The mutational process is blind, natural selection is not. Mutation generates random variation, selction sorts out the winners and losers."
Author of this is Sean B. Carroll, professor of genetics at the University of Wisconsin-Madison.
Second, from the textbook, "Principles of Microbiology", R.M.Atlas PhD, University of Louisville, Louisville KY, Mosby Pub. 1995, pg 270, 271:
"The basis of evolution lies in the ability to change the gene pool and to maintain favorable new combinations of genes. Mutation and general recombination appear to provide a basis for the gradual selection of adaptive features."
According to Atlas, the modifications to DNA caused by internal factors are considered "general recombinations". These modifications are not lumped under mutation, although they clearly are changes to the DNA which the cell tries to fight off. In fact, one of the general recombinations is called "transposon mutagenesis". Others involve plasimids, which are acknowledged to be parasitic in the nature of virus invasions. My conclusion here is that the term "mutation" still fits.
The third source is "The Cambridge Encyclopedia of Human Evolution", Edited by Jones, Martin, Pilbeam, Bunney, with foreward by Richard Dawkins, Cambridge University Press, 1999; Ch 7.3 "Mutation and human evolution", page 273:
"Mutation is the source of all diversity that has led to the evolution of modern humans and to their divergence from other primates. However, mutation is an undirected process: it cannot lead to evolutionary progress unless natural selection is also at work".
The matter of what the theory of evolution consists, seems to me to be closed. It consists of two necessary but insufficient premises: (1) mutation to DNA must occur; (2) natural selection must occur. Moreover, the mutation must be a positive contributer to the selection process. Negative mutations are deselected, frequently through the many genetic defects that occur.
Scott's position seems based on the idea that internal genetic clipping, splicing, doubling, tripling, folding, etc. are not mutations. They are not environmental "point mutations", but they are mutations, changing the DNA from what it was, to something different.
Comments?
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The Carroll quote truly bothers me, as I own that book. I really believe that he and I are talking about different things. I hate to argue semantics with an intelligent guy, so let me just say in advance that I may be guilty of sowing confusion....
Look: I am not denying that mutation is not required in the grand scheme of things, nor am I saying that genetic changes other than point mutations can not be considered, in a loose sense, 'mutations'. But, by that sort of reasoning, all genetic changes can be thought of as mutation. Sexual recombination can be thought of as a mutation, simply because it is a new arrangement of genes. Loosely speaking, I suppose, akin to a mutation but this so dilutes the meaning of the word that it loses all usefulness. Most people, when they are talking about mutation, don't mean 'sexual recombination.'
Any way, one of us appears to be misunderstanding the sense in which mutation is required. Your most recent quotes refer to mutation as the ultimate source of all variation; if this is what you've been getting at all along, I plead guilty to being tone-deaf, because the way I read you is that mutation is always the proximate cause of variation. The former, of course, is the sense in which Carroll and others appear to be agreeing with you. I don't deny that sense. The latter, however, is simply false. In a proximate case, you can uncouple all of these things (mutation, selection, evolution, speciation, variation) from one another.
So, if the former was your point and not the latter, then I have been tilting at windmills. Sorry!
Another comment, this time on the book edited by Jones, et al. My copy of this book is in storage, so I don't know who is actually responsible for this quote:
"Mutation is the source of all diversity that has led to the evolution of modern humans and to their divergence from other primates. However, mutation is an undirected process: it cannot lead to evolutionary PROGRESS unless natural selection is also at work".
Emphasis mine. The word 'progress' is DEEPLY misleading. It implies goal-directed behavior within selection. There is no goal, only an interaction that favors certain lineages over others in a certain environment. What they mean by 'evolutionary progress' is like the way water flowing down a hillside will occupy a certain channel of least resistance, while other paths, less clement, are gradually marginalized or eliminated. One season's alluvial flow is not better in any ultimate sense than the previous season's.
Steve Jones, one of the editors, signed the article referred to, but it's not clear who contributed to it. There are over 70 contributers listed up front. Also not sure if was peer reviewed.
If mutation is defined as "a deviation from the norm", then normal exchange of DNA strands to combine into a new, unique individual would not be a mutation.
Below, deviation is referred to as "hereditary variants", which he classifies as mutations.
Another quote from the same book, this time an article edited by J. Marks, Sec 8.2, pg 299, titled: "Chromosomal evolution in primates":
"Evolution proceeds by the differential proliferation of hereditary variants that arise from mutation. These genetic changes fall into two broad classes: genic or DNA mutations, which can be inferred but not observed, and chromosomal mutations, which involve directly visible rearrangements.
Genic mutations result primarily from substitution of one nucleotide for another, an event that occurs with a low but predictable frequency. By contrast, chromosomal changes arise from the breakage of chromosomes in two or more independent locations and their subsequent reunion - events most unlikely to be repeated."
The term "differential proliferation" would stand for "selection", it seems.
As for mutation being the proximate cause of evolution, it is clear to me that mutation alone could not produce it. It would require selection of positive variances. So the list of rules - if can be allowed to call it that - is that for evolution to occur:
(1) a mutation must occur to the DNA - by whatever means;
(2) Selection of the organism bearing the mutated DNA must occur.
Both (1) and (2) are necessary but not individually sufficient conditions; (1) and (2) together form sufficiency for evolution to occur.
This taken together with an definition of mutation as given above... "a deviation from the norm", maybe we can come to an agreement here, and move on to more interesting portions of the evolution issue.
More interesting to me is the statistical liklihood of a single mutation event - of whatever type - producing a positive variation which will aid the mutant in the selection process.
There are obvious examples of the obverse of this, such as Down's syndrome, sickle cell, and many other genetic defect problems.
More interesting to me is the statistical liklihood of a single mutation event - of whatever type - producing a positive variation which will aid the mutant in the selection process.
There is no way to calculate the likelihood of such a mutation without knowing what a 'positive variation' would constitute, and in what environment. Increased fitness is situation-dependent; without a very high degree of selection, a single point mutation's contribution to increased fitness is going to be difficult to easily detect, much less measure.
Anyway, your mental model of how evolution proceeds comes across as weirdly constrained to this observer. You seem to visualize it as an exclusively 'all-in-one' process, as in, individual gets positive mutation, then evolution occurs in that generation. But that may not be the case. Variation could be produced and lie dormant within the population for many generations in the absence of selection. This is what I mean when I say that while mutation is an ultimate source of variation, it may not be the proximate source of evolution itself. Bacterial clones could have identical mutations, and yet one population of clones might not evolve and another might based upon their local environment.
Scott, my impression is that the idea of accumulation and storage of mutations (evolutionary capacitance)is not considered a viable process under modern theory. I will look further into this, since it fits into the question of how probable evolution is, with or without capacitance.
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