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The Discontinuous Fossil Record Refutes Darwinian Gradualism

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  • #61
    Originally posted by rogue06 View Post
    You're trying to explain this to someone who can't understand that mutations can occur at the same time and aren't always sequential steps.
    Yes evolution takes place in diverse populations.
    Glendower: I can call spirits from the vasty deep.
    Hotspur: Why, so can I, or so can any man;
    But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

    go with the flow the river knows . . .

    Frank

    I do not know, therefore everything is in pencil.

    Comment


    • #62
      Originally posted by lee_merrill View Post
      Bechly is talking about transitions to new body plans in 5 to 10 million years, such as in the Cambrian explosion. If this is indeed in the lifespan of an average species, then this is too short for Darwinian evolution.

      Source: Berkeley

      In perhaps as few as 10 million years, marine animals evolved most of the basic body forms that we observe in modern groups.

      Source

      © Copyright Original Source



      Blessings,
      Lee
      I have described the severe problems with Bechly's ID proposal that gradualism in evolution fails, and your objections to punctuated equilibrium. Now we will deal with the evidence that supports how terrible Bechly's assertions are avoiding the known evidence of evolution. It takes only one amazing fossil site that shows the very rapid evolution of mammals, plants and insects within one million years of the Cretaceous extinction event that wiped out the the dinosaurs, and mush of the diversity of life. That fossil site is the corral Bluffs site in Utah.

      This site not only demonstrated the rapid evolution form a small number of generalized mammals, plants and insects to many specialized species adapted to environmental niches, In this site the mammals at the end of the extinction event were very small generalized feeders that were omnivores feeding on anything available in a devastated environment. The specialized and larger mammals all died out. In the first million years mammals diversified in many different specialized mammals of many different sizes, reflecting rapid diversifitication of pants and insect food sources.

      The bottom line is the changes in the environment rules evolution and not the necessity of the amount of time needed for evolution to take place.

      PBS has a fantastic program on the Corral Bluffs site; See:


      Source: https://www.corralbluffs.org/geology



      Geology and Paleontology of Corral Bluffs


      Corral Bluffs and Jimmy Camp are important because the rocks tell the story of dinosaurs, the extinction of 75% of species on Earth and its subsequent recovery leading to the origin of our modern world . The Denver Museum of Nature & Science has been conducting research concerning the ancient environment surrounding the K-Pg (K-T) boundary in Corral Bluffs and Jimmy Camp since 1991. The University of Colorado, Colorado College, University of New Hampshire and The Smithsonian Institution have also conducted research here.



      The rocks of Corral Bluffs were deposited as the Rocky Mountains were uplifting and simultaneously eroding, rivers and flood waters carrying off the debris. During that process exquisite fossil skulls of rare mammals were preserved in hard rock packages called concretions.



      At that time, 66 million years ago, Corral Bluffs was barely above sea level; the climate was subtropical, similar to that in Florida today. Evidence for this climate is found in leaf and tree fossils, as well as fossils of turtles and crocodiles.



      Over 1,000 vertebrate fossils, 6,000 leaf fossils and 37,000 fossil pollen grains from Corral Bluffs have been collected and analyzed by Dr. Tyler Lyson and Dr. Ian Miller of DMNS and their colleagues to reveal the ecosystem, temperature, climate and location of the K-Pg boundary.

      © Copyright Original Source




      The reason why Bechly lacks any credibility in science is not the volumes of his scientific journal publications, but his dishonest ID agenda ignoring the obvious evidence such as the Corral Bluffs site that demonstrates his agenda is false.
      Last edited by shunyadragon; 12-14-2021, 12:15 PM.
      Glendower: I can call spirits from the vasty deep.
      Hotspur: Why, so can I, or so can any man;
      But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

      go with the flow the river knows . . .

      Frank

      I do not know, therefore everything is in pencil.

      Comment


      • #63
        Originally posted by TheLurch View Post
        Why do you accept his authority but not mine?
        There are many reasons, actually, one of them being that I object to bare arguments by authority, in matters where I can deduce a conclusion.

        Blessings,
        Lee
        "What I pray of you is, to keep your eye upon Him, for that is everything. Do you say, 'How am I to keep my eye on Him?' I reply, keep your eye off everything else, and you will soon see Him. All depends on the eye of faith being kept on Him. How simple it is!" (J.B. Stoney)

        Comment


        • #64
          Originally posted by Stoic View Post
          Once various species are well established, you would expect a new species to be similar to a previous one, because selection pressures would discourage major changes.

          That wasn't the case during the Cambrian explosion.
          So let's say selective pressures changed, at the Cambrian-Ediacaran boundary. This would affect species longevity for Ediacaran species, but not, I think, for Cambrian species, since I also expect that selective pressures would stay fairly constant throughout the Cambrian.

          Blessings,
          Lee
          "What I pray of you is, to keep your eye upon Him, for that is everything. Do you say, 'How am I to keep my eye on Him?' I reply, keep your eye off everything else, and you will soon see Him. All depends on the eye of faith being kept on Him. How simple it is!" (J.B. Stoney)

          Comment


          • #65
            Originally posted by rogue06 View Post
            Don't just guess. What does he mean? And not what you figure he might mean.
            But all I can do is make a best guess at to what Bechly means.

            And when you are filling ecological or environmental niches, development (evolution) can be rapid.
            Are you saying that radiations like the Cambrian explosion were due to filling niches?

            Blessings,
            Lee
            "What I pray of you is, to keep your eye upon Him, for that is everything. Do you say, 'How am I to keep my eye on Him?' I reply, keep your eye off everything else, and you will soon see Him. All depends on the eye of faith being kept on Him. How simple it is!" (J.B. Stoney)

            Comment


            • #66
              Originally posted by shunyadragon View Post
              In the first million years mammals diversified in many different specialized mammals of many different sizes, reflecting rapid diversifitication of pants and insect food sources.
              That may be so, but new body plans? New animal phyla?

              The bottom line is the changes in the environment rules evolution and not the necessity of the amount of time needed for evolution to take place.
              I might mention molecular clocks here, mutation rates. Of course evolution needs time for it to take place...

              Blessings,
              Lee
              "What I pray of you is, to keep your eye upon Him, for that is everything. Do you say, 'How am I to keep my eye on Him?' I reply, keep your eye off everything else, and you will soon see Him. All depends on the eye of faith being kept on Him. How simple it is!" (J.B. Stoney)

              Comment


              • #67
                Originally posted by lee_merrill View Post
                So let's say selective pressures changed, at the Cambrian-Ediacaran boundary. This would affect species longevity for Ediacaran species, but not, I think, for Cambrian species, since I also expect that selective pressures would stay fairly constant throughout the Cambrian.
                I don't know why you would expect selective pressures to stay constant throughout the Cambrian.

                Also, do you have any idea what the average species longevity was during the Cambrian?

                Comment


                • #68
                  Originally posted by lee_merrill View Post
                  That may be so, but new body plans? New animal phyla?
                  I do not believe this was related to the 'Bechly' assertion of the limits of 'Darwinian gradualism' evolution which was proposed in the opening of the thread. I am addressing that, and yes his assertions fail for reasons given

                  No need for new body plans and phyla. You know natural selection, what works survives. There are organic structural developmental limits on the possible survivability of other different 'body plans.' The successful body plans and phyla evolved in Precambrian/Cambrian under evolutionary conditions not present later in the history of life. Simply any potential life precursers for new body plans and phyla would have been eaten in any attempt of later possibility of abiogenesis


                  I might mention molecular clocks here, mutation rates. Of course evolution needs time for it to take place...

                  Blessings,
                  Lee
                  Mention the phony ID clains of the limits of 'molecular clocks' or mutation rates all you wish, but in the history of life on earth their are millions , , , ah, billions of molecular clocks operating at the same time throughout the history of life. My source clearly demonstrated radical evolution and change in the diversity of animal, insect and plant species in less than a million years

                  Let's address Bechly's phony non-scientific assertions based on the religious agenda of ID and not science,.
                  Last edited by shunyadragon; 12-14-2021, 08:37 PM.
                  Glendower: I can call spirits from the vasty deep.
                  Hotspur: Why, so can I, or so can any man;
                  But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

                  go with the flow the river knows . . .

                  Frank

                  I do not know, therefore everything is in pencil.

                  Comment


                  • #69
                    Originally posted by lee_merrill View Post
                    there are many reasons, actually, one of them being that i object to bare arguments by authority, in matters where i can deduce a conclusion.
                    You just made one. In this thread. I pointed it out to you just above.
                    "Any sufficiently advanced stupidity is indistinguishable from trolling."

                    Comment


                    • #70
                      Originally posted by lee_merrill View Post
                      That may be so, but new body plans? New animal phyla?
                      You know what the first species of a new phylum look like? The other species they were related to. Their only difference is a feature or two that they share with subsequent members of that phyla. But otherwise, new phyla arise through the same branching process that produces closely related species, so you won't see any radical differences at the time. It's only in retrospect, when we can see the diversification of their descendants, that we recognize that significance.

                      Put differently, the first members of a new phylum will not have a "new body plan". They will have a body plan that looks very much like that of the contemporary species they're closely related to. It's only due to the subsequent diversification that differences become pronounced.

                      Originally posted by lee_merrill View Post
                      I might mention molecular clocks here, mutation rates. Of course evolution needs time for it to take place...
                      Two errors here:
                      Molecular clocks rely on point mutations, and there are a lot of additional types, many of which (like duplications) can be more important for evolution.
                      Molecular clocks only track the mutations that are retained by modern populations, not the total number of mutations that occurred.
                      "Any sufficiently advanced stupidity is indistinguishable from trolling."

                      Comment


                      • #71
                        Originally posted by lee_merrill View Post
                        There are many reasons, actually, one of them being that I object to bare arguments by authority, in matters where I can deduce a conclusion.

                        Blessings,
                        Lee
                        smiley jawdrop.gif
                        You actually don't realize that this has been precisely what you have been doing in this thread? Making a "bare argument by authority" while now claiming that you object to that?

                        Over and over you have repeatedly shown beyond any doubt that you lack the ability to "deduce a conclusion" in the matters being discussed simply because you have refused to even bother to make the effort to learn even the most fundamental basics of the topics that you ignorantly pontificate on.

                        I'm always still in trouble again

                        "You're by far the worst poster on TWeb" and "TWeb's biggest liar" --starlight (the guy who says Stalin was a right-winger)
                        "Overall I would rate the withdrawal from Afghanistan as by far the best thing Biden's done" --Starlight
                        "Of course, human life begins at fertilization that’s not the argument." --Tassman

                        Comment


                        • #72
                          Originally posted by lee_merrill View Post
                          So let's say selective pressures changed, at the Cambrian-Ediacaran boundary. This would affect species longevity for Ediacaran species, but not, I think, for Cambrian species, since I also expect that selective pressures would stay fairly constant throughout the Cambrian.

                          Blessings,
                          Lee
                          picardfacepalmthumb.jpg

                          It would most definitely affect new species and selective pressures change all the time -- some times fairly drastically -- which is often the reason that periods themselves are subdivided into different stages. For instance, the Cambrian is divided into at least 10 different and distinct stages.

                          Learn the #@%&$ basics and stop spouting ignorant nonsense based solely on what you naively "expect" would happen.

                          I'm always still in trouble again

                          "You're by far the worst poster on TWeb" and "TWeb's biggest liar" --starlight (the guy who says Stalin was a right-winger)
                          "Overall I would rate the withdrawal from Afghanistan as by far the best thing Biden's done" --Starlight
                          "Of course, human life begins at fertilization that’s not the argument." --Tassman

                          Comment


                          • #73
                            Originally posted by lee_merrill View Post
                            That may be so, but new body plans? New animal phyla?


                            I might mention molecular clocks here, mutation rates. Of course evolution needs time for it to take place...

                            Blessings,
                            Lee
                            I believe you need some education on 'body plans and phyla that resulted from abiogenesis and evolution in the Precambrian and Cambrian. They are closely related, and in the history of life the later complex 'body plans' are evolved forms based on the basic 'body plan.' The basic simple geometric 'body plans' are functional in the ability of species to evolve and adapt to more complex 'body plan' forms of the same 'basic 'body plan.' . The following reference is excellent in understanding the nature and evolution of 'body plans.'

                            Source: https://evolution-outreach.biomedcentral.com/articles/10.1007/s12052-012-0424-z




                            The Body Plan Concept and Its Centrality in Evo-Devo


                            Evolution: Education and Outreach volume 5, pages219–230 (2012)Cite this article

                            Abstract


                            A body plan is a suite of characters shared by a group of phylogenetically related animals at some point during their development. The concept of bauplane, or body plans, has played and continues to play a central role in the study of evolutionary developmental biology (evo-devo). Despite the importance of the body plan concept in evo-devo, many researchers may not be familiar with the progression of ideas that have led to our current understanding of body plans, and/or current research on the origin and maintenance of body plans. This lack of familiarity, as well as former ties between the body plan concept and metaphysical ideology is likely responsible for our underappreciation of the body plan concept in its own right, as well as its role in evo-devo. My aim in this review is to outline how we have arrived at our modern definition of body plan, the controversies associated with the concept, its role in evo-devo, and how current research is informing us on body plans. To this end, I integrate concepts such as the nature of phyla, the Cambrian explosion, constraint, evolvability, and results from recent research on gene regulatory networks with the much older concept of the body plan.

                            The concept of bauplane, or body plans, has played and continues to play a central role in the study of evolutionary developmental biology (evo-devo). Bauplan (plural, bauplane) as a term used in biology was first introduced by Joseph Henry Woodger in 1945, and means ground plan or structural plan (Hall 1999; Rieppel 2006; Woodger 1945). Essentially, a body plan is a suite of characters shared by a group of phylogenetically related animals at some point during their development. However, long before the term body plan was coined, its importance was demonstrated in research programs that presaged the field of evo-devo, perhaps most famously (though erroneously) by Ernst Haeckel’s recapitulation theory. Since the rise of evo-devo as an independent field of study, the body plan concept has formed the backbone upon which much of the current research is anchored. The body plan concept is explicit in studies of homology, modularity and integration, canalization, key innovations, heterochrony, variability, evolvability, and arguably all aspects of modern evo-devo research.

                            While I argue that the body plan concept is central to all evo-devo research, its importance is often undervalued or disputed. Many researchers may not be familiar with the progression of ideas that have led to our current understanding of body plans, and/or current research on the origin and maintenance of body plans. This lack of familiarity, as well as former ties between the body plan concept and metaphysical ideology is likely responsible for our underappreciation of the body plan concept in its own right, as well as its role in evo-devo. The importance of the body plan concept in evo-devo research is not a new argument (see Atkinson 1992; Hall 1996, 1999). However, our current concept of the body plan is still largely misunderstood, and I therefore suggest that a review of the body plan concept is worthwhile. Here, my aim is to outline how we have arrived at our modern definition of body plan, the controversies associated with the concept, its role in evo-devo, and how current research is informing us on body plans. To this end, I integrate concepts such as the nature of phyla, the Cambrian explosion, constraint, evolvability, and results from recent research on gene regulatory networks with the much older concept of the body plan.

                            . . .

                            Constraint


                            Constraints can essentially be defined as the limited or channeled generation of variation (Maynard Smith et al. 1985). We recognize such constraints by the disparity in the types of creatures we can imagine and the types that actually exist. For example, we can read and write about griffins, satyrs, and mermaids, but we know that we will never actually see them in nature (Weiss and Buchanan 2009). Such body plans are not possible as a consequence of constraint.

                            In order for selection to act upon an organism, there must be variation. Therefore, as constraint refers to the limited or channeled production of variation, the range of possible responses to selection an organism can display are determined by constraint (Hall 1999). An important aspect of constraint is that it not only limits how much variation is generated, but it also channels the direction of variation generated (Hallgrímsson et al. 2012; Hendrikse et al. 2007). Clearly, much variation exists, as can be seen by comparing horses with turtles, birds, and starfish. Variation exists in multiple directions to allow for such morphological disparity, but it does not exist in every direction. And it is this channeling in the direction of variation that enables some animals to have wings, or shells or hooves, but does not allow for a half-human, half-goat to develop.

                            Constraints are generally thought to arise to ensure that certain structures develop properly. Many of the structures that vary the least in their development (i.e., most constrained) are found to be essential for survival. For example, Galis and Metz (2001) found that organisms exposed to teratogens during the phylotypic stage developed numerous abnormalities resulting in high mortality. The correlation between the development of certain structures and survival is thought to be caused by a relatively large number of inductive interactions between developmental processes (Galis and Metz 2001; Hall 1999; Riedl 1977). Due to numerous interactions with other developmental processes, disruption of central developmental processes (or those that occur during the phylotypic stage) will have widespread effects and thus affect survival. Therefore, to ensure proper development, some processes are constrained in their ability to vary, and this constraint is often maintained by stabilizing selection (Hall 1999).

                            While some structures have essentially remained unchanged for millions of years, suggesting constraints, other traits have changed dramatically and in a relatively short period of time. Structures exhibiting greater diversity have been able to produce more variation on which selection can act and can be described as being more evolvable. Understanding what makes a trait or process more evolvable is one of the main focal points of current evo-devo research (Hendrikse et al. 2007).

                            Evolvability

                            Although there are several definitions of evolvability as described by Pigliucci (2008), I follow the lead taken by Pavlicev and Wagner (2012) and use the definition set out by Lee Altenberg. He defined evolvability as “the ability of a population to produce variants fitter than any yet existing” (Altenberg 1994, p. 47). At first glance, evolvability seems to be constraint’s opposite. While constraint limits the production of variation, evolvability is associated with the generation of variation. However, evolvability is a relational term, such as solubility, and therefore, the concept of evolvability applies equally to all traits whether highly or loosely constrained. Constrained traits are described as having low evolvability, whereas variable traits are considered to have high evolvability.

                            Given that many developmental processes are deeply entrenched within a species, class, phylum, or other taxonomic grouping, evolvability often requires the freeing of development from constraint. But what aspects of the developmental system allow for breaking from constraint? Budd (2006) outlines three properties of developmental systems that can free developmental systems from constraint and generate variation: functional asymmetries, redundancy, and preadaptation.

                            Functional asymmetry is based on Riedl’s burden concept (see below) whereby some structures are more integrated within a system than others. As discussed above under constraints, structures with fewer interconnections are under less constraint and thus, are more variable. Selection can act on this variation to create change. Budd refers to differences in response to selection caused by differences in the degree of connectedness as functional asymmetry and suggests that this asymmetry introduces evolutionary flexibility into the system.

                            In evo-devo, redundancy is often described in terms of genes. For example, genetic redundancy describes the situation where two or more genes have overlapping functions and can either fully or partially substitute for each other (Thomas 1993; Wagner 1999, 2005). However, the concept of redundancy can be applied to any developmental process where overlap between components of the developmental system can substitute for each other, potentially freeing one or more of the components to take on new functions. Budd’s description of redundancy is focused on functional overlap (Budd 2006). He further differentiates redundancy into actual and potential redundancy. When two or more components actually share a common function, they are described as actually redundant. Potential redundancy implies that under the right circumstances, two or more components could share a common function. Potential redundancy is related to the third property of developmental systems described by Budd, preadaptation.

                            Preadaptation refers to the phenomenon of a character acquiring a new function based on its previous or existing functionality. This change in function requires that characters are in the “right place at the right time,” and they must display actual or partial redundancy with the new function (Budd 2006, p. 618). An example of preadaptation provided by Budd (2006) is the change in function developed by feathers. Initially, feathers were used as insulators or for display, but they have since acquired the additional function of flight devices.

                            The initial appearance of body plans, as well as the diversification of traits among species, families, and classes required evolvability of the developmental system. Yet, if we accept Altenberg’s definition (1994) of evolvability, the variants that are produced through flexibility in the system must be more viable than those that already exist. The developmental system must therefore limit to some extent the direction, timing, and amount of variation that can be introduced. Thus, our modern conception of how body plans first arose, their stability over the last 500 million years, and the diversity introduced in later stages of development involves the interplay of constraint and evolvability.

                            Body Plans and the Interplay Between Constraint and Evolvability

                            As stated by Brigandt, “developmental constraint and morphological evolvability are two sides of one coin” (Brigandt 2007, p. 710). This view is similarly presented by Hall (1999) and Hallgrímsson et al. (2012), whereby morphological stability and change are driven by the same developmental and evolutionary mechanisms but in different combinations. Another theme in the modern conception of the body plan is that both adaptive and developmental principles are incorporated (Brigandt 2007; Hallgrímsson et al. 2012). Traditionally, evolutionary theory focused on the interactions between phenotypic variation, selection, and drift, thereby accounting for small modifications of existing structures (Muller and Newman 2005). Thus, evolutionary theory accounts for microevolutionary changes. The origin of entirely new traits, or macroevolutionary changes, fell under a different research program such as developmental evolution (Hallgrímsson et al. 2012; Muller and Newman 2005; Schlosser and Wagner 2004; Wagner and Mezey 2004). As described by Hallgrímsson et al. (2012), marrying adaptationism and development provides an explanation for all evolutionary change, big or small. The first person to bring together these two sets of seemingly contrasting concepts (constraint and evolvability) and mechanisms (adaptation and development) was Rupert Riedl.

                            Riedl brought the body plan concept from its largely metaphysical definition to its current position as a variational concept (Wagner and Laubichler 2004). He noted that the evolutionary patterns we observe, particularly major changes such as the origin of body plans, are more structured than predicted by traditional Neo-Darwinian theory based on population genetics and adaptation (Riedl 1977, 1978). Thus, he reasoned that there is some other underlying mechanism or mechanisms that account for evolutionary change. Instead of abandoning traditional evolutionary theory, Riedl suggested that development structures new variation and that it is this structured variation that is available to selection (Wagner and Laubichler 2004). In this way, Riedl integrated developmental and Neo-Darwinian, or adaptive approaches, to evolutionary change.

                            A main pattern of evolutionary change noticed by Riedl was that different characters evolve at markedly different rates and that traits associated with body plans evolve particularly slowly (Wagner and Laubichler 2004). To explain this phenomenon, Riedl introduced two concepts: burden and evolvability. Burden describes the probability of character evolution based on the importance of that character’s function(s) and the number of other traits that depend on the character in question. A trait has a high burden if many other traits depend on it and if its function is of great importance. Traits with a high burden evolve very slowly. Conversely, a trait with few or no dependent traits, and of minor importance, will have little burden and is free to evolve more rapidly (Riedl 1977; Schoch 2010; Wagner and Laubichler 2004).

                            An important aspect of the burden concept is that burdens are hierarchically nested. As new characters are added, they emerge in the context of the pre-existing characters (Wagner and Laubichler 2004). New characters are dependent on pre-existing traits, thus increasing the amount or rank of the burden of the older traits. In this way, the burden of a trait is considered by Riedl to be directly correlated with its phylogenetic age (Schoch 2010; Wagner and Laubichler 2004). This relationship demonstrates how Riedl incorporated development with Neo-Darwinian ideas of slow gradual evolution. Body plan characters do not arise as body plan characters. Rather, they emerge as novel traits that are not yet entrenched within a species or highly conserved. These new traits are dependent on the traits that came before them, and with time and the addition of new traits, their burden increases until they are essentially fixed.

                            Riedl’s related concept, evolvability, refers to the probability that a new trait arising from mutation will be viable (Wagner and Laubichler 2004). A trait with high evolvability has a relatively high probability for change that will lead to viable results. Riedl noted, however, that most mutations are deleterious and will therefore be selected against. Contrary to what one might initially expect, burden can actually increase the evolvability of a trait. Burden helps to structure variation, channeling emerging variation into directions that are more likely to produce viable phenotypes (Riedl 1977; Wagner and Laubichler 2004). Again, this concept bridges developmental and Neo-Darwinian aspects of evolutionary change. Burden, built into the developmental architecture of a trait or an organism, helps to channel variation that is available to natural selection to produce adaptive phenotypes (or increase evolvability). Therefore, heavily burdened traits, such as body plan characters, provide a developmental framework which can increase the evolvability of other traits within an organism.

                            Schoch (2010) outlines how Riedl’s body plan concept matches our current conception of the idea given the advancements in evolutionary biology. He suggests that Riedl was likely correct in his claim that body plan characters arise stepwise in a gradual manner, and that he was right that body plan characters become increasingly constrained due to internal selection. However, as has been pointed out by several authors, constraints have been found to be breakable (Budd 2006; Maynard Smith et al. 1985; Schwenk and Wagner 2003), and it is therefore unlikely that overcoming body plan constraints is impossible (Schoch 2010). As noted by Meatloaf, “two out of three ain’t bad.”

                            By integrating developmental and Neo-Darwinian evolutionary approaches to the study of body plans, Riedl is largely responsible for bringing the body plan concept from its metaphysical past to its current position at the center of evo-devo research. While Riedl may have missed the mark on a few details, much of his conception of burden, evolvability, and body plans is proving relevant in current studies of genetic regulatory networks (GRNs).

                            © Copyright Original Source

                            Last edited by shunyadragon; 12-15-2021, 08:28 AM.
                            Glendower: I can call spirits from the vasty deep.
                            Hotspur: Why, so can I, or so can any man;
                            But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

                            go with the flow the river knows . . .

                            Frank

                            I do not know, therefore everything is in pencil.

                            Comment


                            • #74
                              Originally posted by Stoic View Post
                              I don't know why you would expect selective pressures to stay constant throughout the Cambrian.
                              Well, the temperature seems to have been fairly stable:

                              Source: Brittanica

                              the global temperature of Cambrian times averaged 22 °C (72 °F). ... Climate studies suggest that Cambrian temperatures were the norm for most of the Phanerozoic Eon (the last 541 million years).

                              Source

                              © Copyright Original Source



                              Though there were some ice ages, apparently, and several extinctions:

                              Source: Wikipedia

                              The sea levels fluctuated somewhat, suggesting there were "ice ages", associated with pulses of expansion and contraction of a south polar ice cap. ...

                              About 515 million years ago, the number of species going extinct exceeded the number of new species appearing. Five million years later, the number of genera had dropped from an earlier peak of about 600 to just 450. ... 500 million years ago, oxygen levels fell dramatically in the oceans, leading to hypoxia, while the level of poisonous hydrogen sulfide simultaneously increased, causing another extinction. The later half of Cambrian was surprisingly barren and showed evidence of several rapid extinction events

                              Source

                              © Copyright Original Source


                              But note that there seem to have been no radiation events comparable to the Cambrian explosion, which would indicate that selective pressures remained fairly stable, if change in selective pressure is part of radiations, which I believe you are arguing for.

                              Also, do you have any idea what the average species longevity was during the Cambrian?
                              Also from Wikipedia:

                              Source: Wikipedia

                              Also, the speciation rate in many groups was reduced to between a fifth and a third of previous levels.

                              © Copyright Original Source


                              Yet species longevity could still remain stable, since longevity does not depend on the speciation rate. I would appeal to Bechly's (and rogue06's confirmation) estimate of about 2.5 to 10 million years, as a long-term average.

                              Blessings,
                              Lee
                              Last edited by lee_merrill; 12-15-2021, 07:59 PM.
                              "What I pray of you is, to keep your eye upon Him, for that is everything. Do you say, 'How am I to keep my eye on Him?' I reply, keep your eye off everything else, and you will soon see Him. All depends on the eye of faith being kept on Him. How simple it is!" (J.B. Stoney)

                              Comment


                              • #75
                                Originally posted by TheLurch View Post
                                ... the first members of a new phylum will not have a "new body plan". They will have a body plan that looks very much like that of the contemporary species they're closely related to. It's only due to the subsequent diversification that differences become pronounced.
                                Well, that's the Darwinian gradualism that is refuted by the discontinuous fossil record.

                                Molecular clocks rely on point mutations, and there are a lot of additional types, many of which (like duplications) can be more important for evolution.
                                Molecular clocks only track the mutations that are retained by modern populations, not the total number of mutations that occurred.
                                But my point is that molecular clocks require time, shunyadragon stated that "The bottom line is the changes in the environment rules evolution and not the necessity of the amount of time needed for evolution to take place." Evolution does require an amount of time for it to take place.

                                Blessings,
                                Lee
                                "What I pray of you is, to keep your eye upon Him, for that is everything. Do you say, 'How am I to keep my eye on Him?' I reply, keep your eye off everything else, and you will soon see Him. All depends on the eye of faith being kept on Him. How simple it is!" (J.B. Stoney)

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