Sunday, February 15, 2015

The null hypothesis of Darwinian evolution

In my last class we discussed the view that natural selection is the only mechanism of evolution (false). We then discussed the view that evolution only occurs when the environment changes (false). Finally, we tried to imagine how any species could become so perfectly adapted to it's current environment that further increases in fitness are impossible (silly).

Along comes a new paper by William Schopf whose earlier claim to fame was the discovery of 3.5 billion year old fossils. A claim that has been discredited. The "fossils" weren't fossils [Did Life Arise 3.5 Billion Years Ago?]. The latest study was funded by the NASA Astrobiology Institute.

I can't read the paper right now because I don't have access but here's the summary from PNAS.
An ancient deep-sea mud-inhabiting 1,800-million-year-old sulfur-cycling microbial community from Western Australia is essentially identical both to a fossil community 500 million years older and to modern microbial biotas discovered off the coast of South America in 2007. The fossils are interpreted to document the impact of the mid-Precambrian increase of atmospheric oxygen, a world-changing event that altered the history of life. Although the apparent 2-billion-year-long stasis of such sulfur-cycling ecosystems is consistent with the null hypothesis required of Darwinian evolution—if there is no change in the physical-biological environment of a well-adapted ecosystem, its biotic components should similarly remain unchanged—additional evidence will be needed to establish this aspect of evolutionary theory.
Ugh! While it might be true that perfectly adapted organisms aren't going to show any new fixations of beneficial alleles in an unchanging environment, that does not mean that there won't be neutral, or even deleterious, changes in its "biotic components."

If we look at the UCLA website, we get a more complete picture of Schopf's views [Scientists discover organism that hasn’t evolved in more than 2 billion years].
The scientists examined sulfur bacteria, microorganisms that are too small to see with the unaided eye, that are 1.8 billion years old and were preserved in rocks from Western Australia’s coastal waters. Using cutting-edge technology, they found that the bacteria look the same as bacteria of the same region from 2.3 billion years ago — and that both sets of ancient bacteria are indistinguishable from modern sulfur bacteria found in mud off of the coast of Chile.

“It seems astounding that life has not evolved for more than 2 billion years — nearly half the history of the Earth,” said J. William Schopf, a UCLA professor of earth, planetary and space sciences in the UCLA College who was the study’s lead author. “Given that evolution is a fact, this lack of evolution needs to be explained.”

Charles Darwin’s writings on evolution focused much more on species that had changed over time than on those that hadn’t. So how do scientists explain a species living for so long without evolving?

“The rule of biology is not to evolve unless the physical or biological environment changes, which is consistent with Darwin,” said Schopf, who also is director of UCLA’s Center for the Study of Evolution and the Origin of Life. The environment in which these microorganisms live has remained essentially unchanged for 3 billion years, he said.

“These microorganisms are well-adapted to their simple, very stable physical and biological environment,” he said. “If they were in an environment that did not change but they nevertheless evolved, that would have shown that our understanding of Darwinian evolution was seriously flawed.”

Schopf said the findings therefore provide further scientific proof for Darwin’s work. “It fits perfectly with his ideas,” he said.
Repeat after me, "Evolution does not equal natural selection. Evolution does not equal natural selection. Evolution does not equal natural selection. Evolution does not equal natural selection. Evolution does not equal natural selection. .."

Here's a question for all Sandwalk readers. How many of you think that the sequences of all modern sulfur bacteria (several thousand species) show almost no evidence of evolution such that phylogenetic trees made with those sequences all have the sulfur bacteria down at the very base of the tree?

PNAS ought to be ashamed of itself. The editor was Thomas N. Taylor of the Department of Ecology & Evolutionary Biology at the University of Kansas who describes himself like this ....
I am a member of the National Academy of Sciences, currently serving a six-year term on the presidentially appointed National Science Board, where I am involved with a variety of science policy issues ranging from K–12 education to support for major infrastructure investments designed to make the U.S. more competitive in research and public science literacy.


42 comments :

  1. It's a stupid paper. We can go and pick out a picture of an extant species of archaea, and compare it morphologically to an extant bacteria, and not be able to tell the difference at all.

    Yet their genetics would show they diverged three and a half billion years ago. The superficial morphology of microorganisms says almost nothing about their environments, for how long, or how much they have been evolving.

    Why doesn't the authors also express surprise that after all this time, life is still based on cells?

    The pretend-flabbergastedness in the press around this paper is almost as stupid as the "it's still just a bacterium" retort one often hears from creationists in response to the long-term evolution experiment. Would they also respond "it's still just an eukaryote" if they saw the transition from fish to tetrapods?

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  2. Considering the limited amount of morphology displayed by sulfur bacteria, this paper is a fine example of the kind of inference paleo data just won't support.

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  3. By the way, Larry. Not to give Quest any encouragement, but have you ever claimed that natural selection doesn't cause speciation?

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    1. Jerry Coyne and I agree that speciation (reproductive isolation) may result from the fixation of neutral alleles by random genetic drift in the separate populations.

      He thinks it is quite rare and I think it is quite common.

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    2. The evidence would seem to suggest that reproductive isolation due to neutral fixation is much less common than fixation due to selection, since it tends to take much longer. That was Jerry's argument. What do you have?

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    3. What is your point? Are you claiming that the evolution of reproductive isolation in all species has to be due to natural selevtion since it always takes place rapidly?

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    4. What is your point? Are you claiming that the evolution of reproductive isolation in all species has to be due to natural selevtion since it always takes place rapidly?

      I've noticed a tendency in you to reach for hyperbole as a first response. The answer is no, because you have stated the hypothesis in an extreme form. I'd say (and the data back it up) that natural selection is usually (not always) responsible for speciation since selection usually (not quite always, given the high variance in the waiting time for rare events) is faster than drift.

      Do you disagree? If so, why?

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    5. Read your initial question. You already knew the answer, didn't you?

      I may have misinterpreted your question. Did you mean to ask if I denied that natural selection could ever cause speciation? Keep in mind that I delete Quest's posts as soon as I see them and I don't bother reading them begore I hit the delete button.

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    6. I'm not sure why I'm supposed to read my initial question, but no, I didn't know the answer (though I admit I had my suspicions). That's why I asked a question.

      Let's forget Quest. What's your opinion of the relative prominence of drift and selection in causing the evolution of reproductive isolation?

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    7. Orr and Coyne observe that there are lots of cases where natural and sexual selection result in speciation and few observed cases where genetic drift causes this result. Moran thinks that probably most speciation results from genetic drift, though natural and sexual selection can sometimes cause it.

      These people agree that speciation occurs and what main categories of processes can cause it, and disagree about what proportion of speciation events can be attributed to each process.

      To conclude from this controversy that speciation doesn't happen would be foolish. Even concluding that we don't know ways speciation occurs would be foolish.

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    8. I speculate that the controversy about the relative importance of natural and sexual selection vs genetic drift in speciation depends in part on the organisms considered. And to some extent on practical considerations.

      Selection for reproductive isolation can occur if differentiated descendent populations meet and have the opportunity to interbreed, and if the hybrids are at some disadvantage. It's possible that animals are more prone to meeting again than are plants. (I may be biased by working recently with two plant groups that disperse poorly and form isolated populations that become different, though retaining the ability to interbreed with related populations they never meet in the wild.) Maybe people working mostly with animals do see more speciation by non-drift processes?

      Speciation can be a long slow process, but we biologists work on relatively quick time lines, even if we spend our working life on a single question. It seems to me that selection for reproductive isolation might occur relatively quickly. Therefore, we have a better chance of seeing it and of finding the evidence for it after it has happened.

      If one population splits into two allopatric populations and they don't meet again, they are likely to diverge even if the environments are similar. Reproductive isolation by mechanisms other than distance is irrelevant. Mutations causing it might or might not occur and become fixed. In fact, they might not occur even after the descendent populations become so different we agree they should be called different species. It seems to me that this process would be hard to study, hard to find conclusive examples of, and common.

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    9. John Harshman asks,

      What's your opinion of the relative prominence of drift and selection in causing the evolution of reproductive isolation?

      My current view is that subspecies become genetically isolated through geographic separation and/or adaptation to slightly different environments. They can persist for long periods of time as subspecies and many of them get classified as species even though they can interbreed if forced.

      The development of actual reproductive isolation takes a long time and is probably due to accidental evolution most of the time. This explains why species like lions and tigers can interbreed even though they have presumably been separated for a long time. Dogs and coyotes are another example of species that have not become incapable of interbreeding, presumably because there was no selective pressure to do so.

      I'm not an expert but from what I understand we don't really know how many closely related species are actually incapable of interbreeding because they have evolved some sort of incompatibility. Scientists have tended to study well-known examples of true and rapid speciation and many of those could be due to specific selection for inability to mate across species boundaries, although the explanation is complicated.

      The cause of speciation.

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    10. Larry, "incapable of interbreeding" is not the generally used standard for speciation. Pre-mating isolation is certainly a major factor, one that doesn't affect capability, merely behavior. And the experimental evidence (summarized by Coyne and Orr) is that partial pre-mating isolation has been achieved in the laboratory and happens much more quickly if the two lab populations are under different selection. Doesn't matter what the selection is for; isolation arises as a byproduct of it. And it arises much faster than if you just leave the populations alone and let drift work on them. That's my argument.

      Note that selection doesn't directly operate on isolation in allopatry; it can't. And can't operate in sympatry unless there's already substantial isolation, i.e. selection against hybrids. That's reinforcement, which is definitely selection and may be part of the speciation process, but it's not at all what I've been talking about.

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    11. Quest,
      I'm confused about your role on this blog or what you are trying to prove here
      The way I see it you bash pretty much everyone atheists, agnostic and religious alike
      What are you trying to prove? Are they all wrong? If that is your problem give something we can digest
      Otherwise it is good for nothing

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    12. you seem blinkered quest.

      Quote "Why should I… or anybody else for that matter, believe that evolution is a fact if two leading scientists, professors, book and textbook writers can’t agree on the mechanism of the supposed factual process…? "

      Thats like saying Christianity is false because Roman Catholics don't agree with Protestants. Your logic is bad . This is what you call ordinary debate within any topic. The evidence for evolution comes things like ERVS,Pseudogenes, Morphological similarities, Fossils in the ground testifying to change over time , example No rabbits in the cambrian rocks. You won't see a mammal before fish and you won't see a bird before reptiles. Junk Dna, the list goes on and on for the evidence of evolution..

      This is how science progresses , by debate.

      We know christianity is false because the bible is rubbish.One look at genesis, noah's flood, Jonah in a fish, Death to firstborns and plagues, Killing witches, Slavery mandates,Death to gays etc etc. Its all falsified trash

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    13. //"Larry, "incapable of interbreeding" is not the generally used standard for speciation"

      What are you talking about....? If you had vasectomy either surgical or "natural" you are a friggen new species because you are incapable of breeding at all.... So what are you... a minion...?//

      I can see why Larry deletes your posts, this is just standard trash from quest. No evolutionary biologist has claimed a definition of speciation so loose that a vasectomy is speciation.

      Everytime speciation is defined you always hear , "genetically incompatible". Having a vasectomy or cutting off your penis has nothing to do with genetic incompatibility. Get some better arguments...You are just looking foolish here

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    14. John Harshman said, in regard to selection:

      "And can't operate in sympatry unless there's already substantial isolation, i.e. selection against hybrids."

      John, I'm confused by your statement. If substantial reproductive isolation of sympatric species/populations is caused (or operated on or reinforced) by selection against hybrids, then how can you say that selection "can't operate in sympatry"?

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    15. Perhaps "can't" is the wrong word. But sympatric speciation seems to be a very rare thing. The model I'm talking about involves near-speciation, i.e. partial reproductive isolation, in allopatry, then a change from allopatry to sympatry between the populations, which have grown different enough that hybrids are disadvantaged. In such a case there will be direct selection against choosing a mate of the other population. The technical term is reinforcement.

      It should be obvious that in allopatry there can be no selection against hybridization.

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    16. John, thanks for your response. I'll put some thought into it.

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    17. Re Prof. Moran

      This explains why species like lions and tigers can interbreed even though they have presumably been separated for a long time.

      It is my information that the male descendants of lion/tiger interbreeding are sterile. Thus, for instance, the coupling of a male and female liger cannot produce descendants.

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    18. Dr. Moran said, "Dogs and coyotes are another example of species that have not become incapable of interbreeding, presumably because there was no selective pressure to do so." Here's some relevant trivia, from an article I read long ago on coydogs, as the hybrids can be called.

      Male and female coyotes are ready to breed at a particular season. Dogs can breed any time a female comes into heat. F1 coydogs are fertile and have a limited breeding season that occurs a few months before the coyote breeding season. Therefore, coydogs can breed with each other or with dogs, not coyotes. In the Midwestern site of this study, the puppies of coydog females were born in snowy February, when they would have died in the wild.

      So there is some selection against interbreeding, though coyotes and dogs are interfertile at this point.

      Of course, this was just one study, and in many places dogs and coyotes share more comfortable climates than the Midwest, so this is probably not the last word on coydog breeding.

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  4. Note that I do not agree with the idea that you can look at the superficial appearance of bacteria and conclude "no evolution". What John said: There is, after all, a limited amount of morphospace available to prokaryotes, and most of their adaptations are 'about' biochemistry. Also, Red Queen Hypothesis; it is unlikely that anything can survive without evolving along with the viruses that it is attacked by.

    Then again, I guess if one were to lean over backwards and be maximally charitable, one could ask: if all the evolution that took place were really in DNA that doesn't matter for adaptation, and the protein function is identical, then who cares? So what he would mean would then be "no evolution that matters to anybody's survival happened in that time". Again, I don't believe it is plausible that it didn't, but my relevant belief would be untestable, and this would be the charitable interpretation.

    Finally, we tried to imagine how any species could become so perfectly adapted to it's current environment that further increases in fitness are impossible (silly).

    This one got me thinking. Again, Red Queen Hypothesis. But I could imagine that an extremely simple prokaryote with very few genes and an autotrophic life style in a very clearly defined niche could conceivably have arrived at the fitness peak a long time ago and found it very difficult to get any better at what they are doing, especially if it did not have any strategy for dealing with predation that went beyond "hope they don't get all of us". For anything that is heterotrophic, however, the issue of co-evolution with their prey or, in the case of destruents, their substrate arises immediately.

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  5. When I read about the sulfur bacteria, I thought, OK, they look alike, but then most bacteria do (forgive me, microbiologists!). What about their genetics, their physiology? Of course, there's no direct way to know. It would be interesting to see a phylogeny of these things. I'd be surprised if there really hasn't been change. But it would be really interesting if there weren't. I wonder if we could tell.

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  6. I think it's worth looking at a 1975 paper: "Genomic Versus Morphologic Rates of Evolution: Influence of Morphologic Complexity". In this the authors propose that the number of preserved traits (i.e. the morphologic complexity) lead to an effect where a large ammount of variablity in observed morphological rates of change is produced by clocklike molecular evolution. Now this is rather obviously relevant to the Paper by Schopf et al. 2015, since the number of morphological traits preserved in sulfur bacteria is low. It also has a different type of relevance. The 1975 paper is by Schopf et al. - T.J.M. Schopf in this case, J.W. Schopfs brother. It appeared in the first issue of Paleobiology, a journal founded by Tom Schopf - following his editorial work on "Models in paleobiolgy" (1972).
    Finally the paper is relevant because it is the 3rd of the 4 MBL papers, which describe a neutral null model of morphological evolution in deep time. This null is not a model in which traits are preserved in the absence of selection, but where a neutral baseline exists and selection can either increase or decrease this rate of change.
    Now, I fully expect this to be discussed in the paper. I doubt Schopf doesn't discuss his work in relation to that of his brother. And I'm also pretty certain there are a few "morphological"s missing from the UCLA quotes. They are usually at least implied by paleontologists (and if I had a buck for each time I had to explain to somebody that punctuated equilibrium is about morphological rates and not molecular rates, I wouldn't be rich, but I think I could buy myself a rather lavish dinner). One thing I'm learning from working with molecular biologists is that I need to spell out some things I don't have to in paleontolgist circles, because if I talk to the latter and say rate of evolution, they think "morphological rate of evolution", while among neontologists the immediate instinct always is "rate of sequence evolution". In the same way, it's always clear to paleos that having a fossil does usually not mean having access to all character states in a phylogenetic matrix. That's not the case with recent material, where you can always check the additional states, while for the fossils the relevant morphology might simply be absent.
    There is a fairly decent chance that you misunderstand Schopfs view based on these differences in jargon across disciplines, Larry.

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    1. Let me know if you agree with each of the following statements.

      1. The term "Darwinian evolution" is a correct description of modern evolutionary theory.

      2. Modern evolutionary theory predicts that there will be no change in the "biotic components" of a species over time in a constant environment.

      3. Some species have lived in a completely unchanging environment for several billion years.

      4. An examination of very ancient fossil bacteria reveals that they are absolutely identical in morphology to one of the several thousand species of living sulfur bacteria.

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    2. 5. “These microorganisms are well-adapted to their simple, very stable physical and biological environment,” he said. “If they were in an environment that did not change but they nevertheless evolved, that would have shown that our understanding of Darwinian evolution was seriously flawed.”

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    3. 6. By referring to "evolution's null hypothesis" in the title of a PNAS paper it should be obvious to everyone that the paper is only referring to the narrow restricted view of evolution of paleontologists; namely, observable morphological change

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    4. 7. It is impossible for observable morphological chage to occur by the fixation of nearly neutral alleles due to random genetic drift.

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    5. 1. No. But "Darwinian evolution" is regularly used for cases where there is significant positive selection. I'm not a great fan of this usage (mainly because Darwin did not use selection in this way). It's worth noting that you use non-darwinian evolution in cases where there's no significant selection as well (again, I'm not overly happy with that usage).
      2. No. As noted in my post that's not even a general null for morphological evolution and it certainly isn't one for molecular evolution.
      3. Define "unchanging". There are certainly environments that have had relatively stable conditions for long periods of time. In this case this seems to refer to the change in oxygen concentrations before and after the great oxidization event (i.e. the time when organisms capable of photosynthesis started to lead to an increase of oceanic oxygen from close to nothing to ~20% for the top layers). AFAIK oxygen concentrations are bistable, i.e. you can't really have longer periods where it's close to 10% or so, you either are <<1% or at ~20%. And after the GOE concentrations never dropped back to the pre-GOE levels. So this particular feature of earth was relatively stable (there are of course changes in oxygen concentrations over time, but they are small compared to the turnover at the GOE).
      4. I'm not working on bacteria, so I couldn't say. But it is worth noting that not all features of bacteria are preserved as fossils. Also the Schopf et al. 2015 article states that there are similarities in the distribution pattern of the bacteria. Again I do not have the expertize to judge whether that's an artifact or not, because I do not know how diverse these patterns are in the recent. It's worth noting that Stromatolithes are structurally similar to recent stromatopores, so we know cases where bioherms have conserved some macroscopic patterns.

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    6. 5. I don't agree with this statement, but I'm wary that this represents a excerpt from an interview.
      6. It isn't. And I would reject the notion that paleontologists have such a "narrow, restricted view of evolution". But we are aware that our data does not permit us to directly make inferrences about molecular changes. When writing a paper for a paleontological journal you don't have to emphasize that point (I recently published one which dealt with fossil leaves and it does not mention explicitly that not all of them are complete for instance. No reviewer complaint, because that goes without saying in the field). I agree that for a journal like PNAS that is aimed at the general scientific community these things should be made explicit. But I can also understand how that's something that gets missed by authors who are primarily interacting with people in their own field and the reviewers recruited by the journals, who tend to shere the same biases. It goes both ways, BTW. I've set through talks where a biomathematician was referring to the "model" all the way through and never made explicit what type of model they were referring to. It meant "substitution model", but in that particular neck of the woods that's something that goes without saying.
      7. I'm somewhat on the fence here. Changes in morphology that leave a fossil record tend not to be things that are likely anywhere near neutral. That doesn't mean we have to fall into adaptionist traps, but it's rather clear that near neutral changes account for more of the molecular changes than for morphological ones. By how much is very much debatable, mainly because we do not as of now have a universal theory of how genes affact phenotypes. It's also worth noting that there are neutral models in paleobiology, but they do not neccessarily assume an absence of selection, but rather an absence of a consistent direction of selection in deep time. When you have selection favoring a change of a quantitative trait in one direction sometimes and in the other some other time, you do get a neutral model (a molecular analog is Kimuras work on an allele with stochastically fluctuating s, where the mean of s in time is 0. Even if |4Ns|>1 for all times, indicating that there is always significant selection a mean s of 0 means that you have a long term behaviour indistinguishable from the neutral case).
      One should be as wary of extrapolating the near neutrality of most molecular evolution to a near neutral theory of most morphological change in deep time as of using selection as the cause of trends in deep time.

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    7. It seems to me that 'cryptic' species are at least somewhat relevant to this discussion.

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  7. Natural selection is still the only unguided evolutionary mechanism said to be able to produce design without a designer.

    Just sayin'...

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    1. Hey joey, can you produce a link to an evolutionary scientist (or better yet a whole bunch of evolutionary scientists) saying that "Natural selection is still the only unguided evolutionary mechanism [...] able to produce design without a designer."?

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  8. I know cops write more traffic tickets at the end of the month when they need to meet a quota. Do the scientists at some institutions have a quota on the number of papers they publish? If so that would explain this paper.

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  9. Well, it *is* true that Charles "dead as a door-nail" Darwin believed that there would be no change by "natural selection" without a change in environment. And most biologists apparently are still following this dead guy's views.

    But haven't we been over this whole issue before, without any resolution? That is, there are other cases in which gross morphology has not changed for a long time, as for some sharks or brachiopods or the Coelocanth or the horse-shoe crab. And we have had a discussion about the reasons for the lack of apparent change, and the issue is not resolved.

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  10. For laymen like myself, we probably use the term 'natural selection' because all selection types in nature are a result of natural processes; there is no evidence of supernatural selection. (There is artificial selection in food production, but I'm not sure that really counts at all.)

    Dave Bailey

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  11. This is all compost in a crackpot. There is virtually nothing that can be inferred about the genetic or biochemical properties of a bacterial or archaeal organism by looking at it. A rod is a rod is a rod. Back when Larry and I were young, Archaea and Bacteria were both called "bacteria," and it wasn't until Carl Woese analyzed the rRNAs that their phylogenetic diversity became apparent.

    The paper even admits, quoting Simpson, that their observation "does not necessarily imply genomic, biochemical, or physiological identity between modern and fossil taxa."

    I'm willing to admit that their sulfur isotope data are consistent with a sulfur-based metabolism, but that's as far as anyone can go.

    There, Larry, I've saved you the time it would take to read this paper. You can thank me later. ;)

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  12. "What are you talking about....? If you had vasectomy either surgical or "natural" you are a friggen new species because you are incapable of breeding at all.... So what are you... a minion...?"

    Irrelevant. The smallest unit to which evolution can be said to occur is the GROUP, not the individual. The reference was to when aGROUP cannot interbreed with ANOTHER GROUP sufficiently to produce [enough] viable, fertile offspring.

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  13. I’m posting below a few random quotes from Schopf et al PNAS paper for the readers who don’t have access to it. I’m probably wrong, but I can’t escape the thought that this paper is a sophisticated Sokal case ( http://en.wikipedia.org/wiki/Sokal_affair).

    On that note, I agree with Schopf et al that “The marked similarity of microbial morphology, habitat, and organization of these fossil communities to their modern counterparts documents exceptionally slow (hypobradytelic) change that, if paralleled by their molecular biology, would evidence extreme evolutionary stasis” , which means that if *not* paralleled by their molecular biology then, the claim will be redefined as a case of “Volkswagen Syndrome”; so, either way, the authors are ‘hypobradytelically’ right, a genuine Sokal attribute.

    “Similarly, the dominant microbial components of the two assemblages are essentially identical: relatively large diameter (∼7- to 9-μm-broad) elongate-celled filaments (Fig. 2 B−D and F−H), smaller diameter (∼1- to 4-μm-wide) filaments composed of bead-shaped cells (Fig. 2 L−U), and very narrow (≤1-μmdiameter) thread-like cellular filaments (Fig. 3 D−I)—morphotypes that differ from phototrophic cyanobacteria (6, 10, 11) but closely resemble principal components of the anoxic subsea floor parts of modern sulfur-cycling communities (9, 10) off the western coast of South America (Figs. 2 and 3), modern communities that exhibit an irregular web-like fabric similar to that of the fossil assemblages (compare Fig. 1 A−F with figure 10 in ref. 10) in which many of the “bead-celled” filaments contain sulfur granules (ref. 10, figures 6 and 7), products of anaerobic sulfide oxidation."

    "Although speciation-based evolution occurs at the phenotypic rather than genotypic level of biologic−environmental interaction, the biomolecules underlying such change are not preserved in the rock record in which such assessment can be based only on indirect proxies and inferences of physiology based on isotopic analyses."

    "Moreover, large-diameter (“giant”) sulfur bacteria of differing phylogenetic lineages can exhibit similar morphologies and patterns of behavior suggesting convergent evolution of morphologic “look-alikes” adapted to a same or similar function (46, 47)."

    "Although it remains to be established whether such morphological “mimicry” is exhibited also by the more narrow ≤10-μm-diameter sulfur bacteria described here—the two modern sulfur bacterial taxa of similar dimensions being aerobes (ref. 46, table 2) rather than anaerobes like the Duck Creek and Turee Creek fossils—it remains conceivable that the marked similarities between the two mid-Precambrian communities and their modern counterparts could be an example of the so-called Volkswagen Syndrome, a lack of change in organismal form that masks the evolution of internal biochemical machinery (6).”

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  14. Larry, it seems that these two statements of yours are in direct contradiction:

    "Finally, we tried to imagine how any species could become so perfectly adapted to it's current environment that further increases in fitness are impossible (silly)."

    "While it might be true that perfectly adapted organisms aren't going to show any new fixations of beneficial alleles in an unchanging environment, that does not mean that there won't be neutral, or even deleterious, changes in its "biotic components.""

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