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    Mosaic Evolution Versus Punctuated Equilibrium: Morphological Traits Within Fossil Species Lineages
    By News Staff | November 27th 2012 10:30 AM | 23 comments | Print | E-mail | Track Comments

    What happens when the modern evolutionary theory of punctuated equilibrium collides with the older theory of mosaic evolution? That's the issue addressed by paleobiologists Melanie J Hopkins at the Museum fuer Naturkunde Berlin and Scott Lidgard at the Field Museum in Chicago.  

    While processes of evolution are largely studied by observation and experiment in the living world, evolutionary tempo and mode – rates and patterns of change, respectively – are mostly revealed by studying the fossil record.

    Paleontologists measure parts of the hard skeletal fossil remains of once-living organisms that they believe best represent the morphology, or form, of those organisms and then analyze the variation in these traits through successive layers of rock that were laid down over longs spans of geologic time in order to determine the tempo and mode of species evolution.

    Punctuated equilibrium postulates that most evolutionary change takes place in relatively short periods of time during the origination of new species, while species themselves mostly undergo stasis, or little change, over longer periods. Mosaic evolution is the tendency for different parts within species to evolve in different ways or at different rates. 
    Several recent studies have indicated that stasis is much more common than gradual directional change in the fossil record.

    A new study based on data taken from hundreds of sequences of fossil samples previously reported in the scientific literature compared models describing different modes of change, namely stasis, random change, and directional change, to each fossil series and found that different traits generally showed different, conflicting evolutionary modes within the same species. Many kinds of life were represented, including mammals, fish, mollusks, arthropods, and single-celled organisms.

    This large comparative study validates the ubiquity of mosaic evolution but also raises questions about the evidence for different evolutionary modes, since the great majority of previous studies that quantify stasis, punctuated equilibrium, and gradual or "random" patterns in the fossil record are based on measurements of single traits, not on combined analyses of many traits.

     Further research will be required to establish the underlying processes driving the patterns of mosaic evolution and fossil species change. 



     Published in the Proceedings of the National Academy of Sciences (PNAS).

    Comments

    NY Times science writer Nicholas Wade offers the following compromise to settle tempers on two angry sides of American thinking: Let's go back to calling it "the theory of evolution". From his column:

    Evolutionary biologists are furiously debating whether or not natural selection can operate on groups of individuals, as Darwin thought was likely but most modern evolutionists doubt. So which version of evolution is the true one?

    By allowing that evolution is a theory, scientists would hand fundamentalists the fig leaf they need to insist, at least among themselves, that the majestic words of the first chapter of Genesis are literal, not metaphorical, truths. They in return should make no objection to the teaching of evolution in science classes as a theory, which indeed it is.

    Hank
    I think the fundamentalist aspect of this whole 'debate' is trumped up by people who need to be hyped up about something.  Evolution teaching and religion is not a national issue - we are less religious than we have ever been and yet we led the world in Nobel prizes when we were more religious.  The difference between America and other countries is that media here, especially in science, have polarized themselves around core political issues and one of them is evolution and worrying if some crank school district somewhere tries to be stupid.

    Young Earth Creationists can believe whatever they want and it makes no difference at all, because those kinds of people never went on to become scientists anyway. The evolution 'debate' is just another way for each side to drum up votes for its candidates - Republicans are anti-science and Democrats are immoral atheists.
    We may be less religious, but we're still pretty religious. Have you heard anything about the new Common Core Science Standards lately? I think that committee is deadlocked around how to handle the teaching of evolution. This is why we now DIPLOMACY, NEGOTIATION, and COMPROMISE, since DEBATE got us nowhere.

    Hank
    Well, we can't vote on science.  Compromise on science and you get terrible science.  Evolution is hard - even for biologists - and I have floated the idea of not teaching it in public school because most science teachers don't understand it properly, and the same surveys that gripe about the public not accepting it show teachers don't get it.  Like we teach quantum physics in college but Newton in high school, and brain surgery in medical school but anatomy in high school, we could teach genetics in high school and it would be no issue and save the complexities of evolution for college. It seems to be mostly vanity that makes biologists insist evolution has to be taught - physicists are not worried if string theory is not covered until college.

    I say floated the idea. No one agrees with me so it hasn't floated, it has sunk like a rock.

    Since the Common Core Science Standards are also the toothless things that committees come up with, and won't be adapted, what they decide is almost as meaningless.
    I don't blame electoral politics or the media for all the high blood pressure surrounding this issue. I think that it all points to education, people's fear that somebody is going to use their authority to contradict me to my children.

    What do you think can be done to assure parents that this isn't going to happen? ...because you know that both sides use Origins as a stepping-stone for propagating their personal philosophical / religious / anti-religious perspectives.

    ...your idea to leave Evolution out of primary education nonwithstanding, since there's no support for it...

    Hank
    I think both Young Earth Creationism and militant atheism are fads. I am in my 40s and neither of those movements existed when I was a kid, to any degree where it was noticeable. Despite the fact that I lived in a town of 200 people, with 5 churches, no bars and no red lights, I never once heard about religion in a science class.

    In the early days of the NCSE, religious people were 100% in support of science and keeping religion out of schools, because they did not want to spend Saturday and Sunday discussing a sectarian view taught Monday through Friday by the government. But once the militant cranks called every religious person a 'creationist' religion was forced to take a side.  The goofy demographic in academia is far out of the mainstream but they try to hijack the discourse for everyone. All that does is send money to religious groups who don't do any research at all, they just promote doubt about evolution.
    Who has the ability to set this discourse back on track, in a way that endures?

    Scientists? Academies? Authors? Journalists? Government? Educational institutions?

    How would you do it?

    Hank
    I would ignore it the way Europe ignores it. They are incredibly anti-science about some things but they don't have the evolution issue because the militants are protesting nuclear power and cell phones so anyone trying to get religion taught in science classes would be laughed at.

    I think Americans who go on about the issue are the idle rich, compared to the rest of the world.  They need to live in important times so they create problems to solve.
    This is not about religion, this is about science. So back to science!

    Although Gould should be considered as one of the major forces in Evolutionary Biology, unfortunately his and Eldredge go utterly wrong with this "theory". Not that it is incorrect, it does not explain anything. OK it explains the fossil record, but how is it really a scientific explanation? The fossil record is not gradual, hence evolution was not gradual. That just pushes the question higher up. It is like a Deus ex Machina.

    Can we explain it? Of course. Too much to put here but think in that we know that evolution occurs more at the level of regulation (=scientific fact) and it all makes sense. A single mutation in for instance a homeodomain or a promotor region of an important transcription factor is bound to have a strong phenotypic result. This is still not the complete story: because of the phenotypic change the organism needs to change ecological niche. As a result the functional constraints change and break stasis and speed up evolution.
    Add this does not go against mosiac driven evolution. Both are so to say the result of mutations in genes, with gene in its broadest sense. It just depends what kind of mutation, what kind of gene is was in the first place. Please do not explain things at a high complexity level when you can do it a the gene level since you are bound to overlook things.

    Hi Arjen ten Have,

    Do you have a minute to discuss a question about a limitation I see for science?

    What would the scientific explanation be for each of the following questions:

    1) Why does the Universe exist?
    2) Why do Earth and the things in space look the way they do?
    3) How did all the different life forms on Earth appear at first?
    4) If I find a life form that's really amazing, where should I apply the credit for its amazingness?
    5) How did life begin?
    6) Why do I feel bad when I do some things?

    Arjen, each of these questions (unless I made a mistake) can't be resolved by science, i.e. experimentation and confirmation. But people feel the need for some kind of explanation, so they turn to the smartest people they know to see what they think. That's where SCIENTIFIC EXPLANATIONS come from.

    I think that identifying what it is that scientific explanations explain will help everybody find agreement on how we should talk about these things in public, especially since it seems clear that Science is only one of several valid voices that people choose to answer the questions.

    Gerhard Adam
    If I might interject.  Part of the problem is defining the context in which these questions are asked.  For example #6 [Why do I feel bad when I do some things?].

    On a personal level, it may be because you've done something wrong.  From a philosophical level it might include discussions about morality, etc.  From a scientific perspective we could talk about chemicals in the brain.  Each are valid within their appropriate context.

    Similarly, if we understand that science takes it as axiomatic that one cannot invoke magic or divine powers [since they are not subject to testing], then it becomes easier to see why arguments that attempt to introduce these elements are unscientific.  They may be perfectly valid within their respective contexts, and they could even be correct, but they aren't scientific.
    Mundus vult decipi
    Gerhard,

    This is exactly my point. In short, "Science can't explain everything" and "Unscientific explanations aren't categorically false."

    I want to make room in our public discourse for "Unscientific things that might be true", and to avoid the fallacy that "Science is the best resource for answers to absolutely every question."

    Gerhard Adam
    Yes, but that also depends on what you mean by answering questions.

    If a question is subject to experimentation, verification, etc. then science is the best explanation for what occurs.  In other words, it's the most objective means by which something can be understood.

    However, if something isn't subject to testing, then we only have two options.  Either it is something that is strictly subjective and a matter of opinion [i.e. I like this song or food, and I dislike something else], or we can use the information we do have scientifically and see how a particular topic fits into that.  After all, if science has established something as being correct, we can't simply circumvent it and make science conditional on our own opinions.

    A simple example.

    Suppose someone wants to suggest that ghosts are haunting their house and moving the furniture around [or something like that].  Well, science certainly hasn't proven that ghosts don't exist, and someone may insist that they've experienced it, so their view is equally valid.

    However, scientifically we do know that to move furniture requires a force, and Newton's laws require that for every action there is an equal and opposite reaction.  So from this, we can conclude that for a ghost to move furniture requires that it have a physical interaction with our environment.  At this point, it can obviously not be a ghost, since it must have a physical existence.

    Now if someone wants to insist that the rules of physics are different or they don't apply, now the onus is on them to demonstrate why the laws of physics should break down and under what conditions.  So in the absence of such evidence, we can reasonably conclude that ghosts that interact in such a manner are not possible, given what we presently know regarding physics.

    This doesn't open the floodgates to idle speculation, since whatever is conjectured or suggested must still fit with what we actually do know, or some evidence must be provided for why that is insufficient.

    As a result, we have the problem that for something to be "correct", we may well have to consider that outside of science, such a view may be subjective and incapable of proof.  So, while we may personally believe it to be correct, the failure to make it an objective experience, also means that its "correctness" can never actually be confirmed.
    "Science is the best resource for answers to absolutely every question."
    This is a bit of a problematic statement.  If you ask me a question, then you're either asking for my opinion, or an objective response to the question.  If it is objective, then it is capable of being verified independent of our respective opinions.  If it is only subjective, then I cannot answer your question beyond simply providing my own subjective interpretation.

    This is the problem that many people have between religion and science.  Subjective experiences are not subject to objective proof, so while someone may believe something to be true with every shred of their being, unless it can be objectively demonstrated it isn't scientific and it is simply their subjective opinion.  Unfortunately, too many people take that position to mean that they can override the known science or make it conditional because their subjective view is "true" while science can't prove otherwise.  It should be clear what the fallacy is in that reasoning.
    Mundus vult decipi
    Along with subjective truth (the best ice cream flavor), objective truth (the weather today), allow me to propose a new sub-category: subjective truth that I know about somebody else.

    If you tell me that your favorite ice cream flavor is mint chip, is my knowledge of your preference objective or subjective?

    I think this category deserves separate mention, since this is knowledge that is testable. (So-and-so said that mint chip is your favorite flavor. Is this true?) So it's not subjective to me... to me it's much more firm than that.

    Yet, if you change your mind, or if you no longer live to like or dislike it, my knowledge of your ice cream preference becomes moot. Or wrong.

    But it's still not subjective... it was absolutely true before, and now it becomes absolutely wrong. It's not like I can answer the question, "What is your friend's favorite flavor of ice cream?" any way that I wish... there is only one true answer.

    Gerhard Adam
    Perhaps, but there's a reason why there's a legal definition called "hearsay".  The only thing that is objective is that you heard the individual say it.  The individual may have simply made something up, you may have mis-remembered it, you may have misunderstood, or you may simply have thought that's what you heard.  In all instances, it's still subjective.

    Such knowledge is not actually testable unless there is separate third-party, disinterested verification that the conversation took place [i.e. recording].  However, even in such a situation, you can only confirm that the conversation occurred.  If the individual has changed their mind, then your "objective truth" disappears along with their explanation.  This can't occur for things that are truly objective.  In science such information can't disappear or be changed without good reason, whereas in your example, it can be changed for no apparent reason at all.

    Nevertheless, I would also question whether you could actually claim this information to be "knowledge" or merely something that you've assumed to be true from the source.

    What I will agree on, is that this is often the primary source of much of our information, scientific or otherwise.  We have to establish whether something comes from a trusted source and then we assign the degree of truth to which we will hold that information.  I touch on some of these points in an older post.
    It's not like I can answer the question, "What is your friend's favorite flavor of ice cream?" any way that I wish... there is only one true answer.
    Actually you can say "I'm not sure" or "I don't know".  Also, to be accurate it would be more appropriate to say that "They've indicated in the past that they like mint chip".  In other words, you've shifted the "truth" of this statement back as an indication that your knowledge of this is only second-hand.

    Another interesting aspect of your statement is that only YOU are compelled to be objective in repeating what you heard, if you're honest.  The original source is not.

    I do recognize that this is in a somewhat unique category, but I'm not sure that I would attach as much significance to it as being any less subjective.
    Mundus vult decipi
    OK, now I will say why I think this is an important category. This category is the basis for the religious knowledge held by those Muslims describe as "People of the Book".

    If a person, for their own reasons, believes that God is real and is the source of Scripture, then anything in Scripture is more than subjective to that person. Whatever the Scripture says is something "that a friend told me".

    Now of course, it's totally important to judge whether the friend is reliable. But that's the subjective part. The more-than-subjective part is what the friend said.

    In the case of the Bible, there are a bunch of places where the most important voices (Jesus and God through Moses) "tell me" that they are reliable and that the Scripture is reliable, too.

    So to someone looking at this Bible, the subjective part is whether or not to trust the source. Everything else is more-than-subjective.

    Gerhard Adam
    Regardless of how you choose to interpret it, you cannot claim objectivity from any of these scenarios.

    Since any "truth" is far removed from the ability for verification, it becomes more like a historian's interpretation of old documents.  It must be assessed within the context of other documents, and then perhaps some semblance of the "truth" can be ascertained.  This is one reason why regardless of how important or accurate history may be viewed, it isn't science.  It's simply too interpretative.

    However, to only have a single source and to claim it as accurate, is purely subjective opinion.
    Mundus vult decipi
    I could not agree with you more on each point here. Why do you use quotes ("") on the word TRUTH?

    Gerhard Adam
    I use quotes whenever a word may be ambiguous or subject to controversial definitions.  That way I can indicate that it's in a colloquial use recognizing that there may be a range of definitions that people wish to quibble over. 
    Mundus vult decipi
    Very well.

    Nice chatting with you! (via webs) I wish you a good weekend!

    Gerhard Adam
    You too and have a good holiday :)
    Mundus vult decipi
    By the way, since you have identified yourself I feel it's only polite for me to do the same. See my LinkedIn profile at www.linkedin.com/in/ellioSPAMtsvensson.

    (Remove SPAM from the link).