Notices
Results 1 to 29 of 29

Thread: Cambrian Explosion problem

  1. #1 Cambrian Explosion problem 
    Forum Freshman
    Join Date
    Jun 2008
    Posts
    7
    Hello,
    I'm slowly coming around to accepting Evolution. I do have two major problems with it though: The Cambrian Explosion/Punctuated Equilibrium problem(i.e. 5 million years or less to evolve these forms), and the land-mammal-to- whale/dolphin in less than 5 million years.
    Do any of you have problems with these(and why)? Do I have the time periods right(i.e. 5 million years or less)? Are there any other "explosions" that I ought to know about, or are these the only ones?

    LAGoff


    Reply With Quote  
     

  2.  
     

  3. #2  
    WYSIWYG Moderator marnixR's Avatar
    Join Date
    Apr 2007
    Location
    Cardiff, Wales
    Posts
    5,810
    right ball-park figure, although in reality the cambrian "explosion" was probably a more extended affair, being more an issue of fossilisability : if lagerstatten such as the Burgess Shale have taught us anything it's that the normal fossil record (usually animals with hard parts that live in places that facilitate the formation of fossils) is a woefully inadequate basis on which to estimate the real richness of life at the time

    imo the cambrian explosion has more to do with multicellular beings becoming larger and acquiring fossilisable tissues than with a real, fast-paced evolution

    punctuated equilibrium happens usually at the species level, and Niles Eldredge's original finding was that different species of Phacops remained in place unchanged for extended periods, and then were replaced relatively fast by sister species which seem to have migrated from neighbouring areas after the original species had died out
    so replacement happens quite fast, but it doesn't say anything about how long it took for the sister species to evolve elsewhere

    having said that, observed evolution rates in real-time show that evolution can happen quite fast, but quite often the selection pressures are so varied + often change from one year to the next that evolutionary changes rarely change in a single direction, and seen over extended period may look like stasis
    if, on the other hand, directional selection pressure does occur (e.g. artificial selection by humans), major changes do happen in a remarkably small spans of time - compare for instance the transformation of theosinte into corn in a matter of a few thousand years

    as for the evolution of whales, if the fossil records shows how at the start of the Eocene there was a semi-aquatic quadruped and at the end of it a fully-formed whale, with many intermediates inbetween, who am i to argue with the fossil record ?
    (to be pedantic, the length of the Eocene was closer to 15 million than 5 million, but te point remains the same)


    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
    Reply With Quote  
     

  4. #3  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,168
    Hi Lagoff and welcome to the forum. I am a hard line evolutionist, based upon personal observation of the palaeontological and anatomical evidence. It is only in the last five or so years that I have begun to understand the the much more powerful evidence from genetics and embryology and developmental biology.

    That said the Cambrian explosion remains a problem: but it is important to understand what a problem is in science. Creationists like to identify problems that have been recognised by evolutionists in their particualr field, and hold these up as examples that evolution is in crisis; that's its own adherents doubt the truth of it; that there are insurmountable ambiguities in the data. This is simply wrong.

    A problem can point to a theory in crisis, but in most instances it simply points to an aspect of the theory that has not yet been fully explained, a facet for which the mechanisms and details have not been fully worked out. Such is the case with the Cambrian explosion.

    The remarkable thing about the Cambrian explosion is that we went, in a geologically short time span, from three phyla to around thirty three. No new phyla (with one possible exception) have appeared since then. So two questions arise: why did this remarkable introduction of diversity occur then; why has it never occured since? Those questions certainly constitute a problem, but in the sense of a challenge, not an obstacle. There is no reason to expect that we shall not come up with an answer - several researchers would claim that they have - and every reason to expect that we shall.

    On the subject of punctuated equilibrium, the sparsity of the fossil record mentioned by Marnix makes it difficult to decide whether the apparent punctuations ar real or are a sampling artifact. The jury still seems to be out on this, but either way it does nothing to invalidate or challenge evolutionary theory, it merely modifies and refines it.
    Reply With Quote  
     

  5. #4  
    Forum Freshman
    Join Date
    Jun 2008
    Posts
    7
    Thanks,
    I am pretty much illiterate when comes to Evolution. I'll have to read.

    There is a question: I think species remain stable. Like if you take a Chihauaha and a Saint Bernard and put them in the wild, in a short time they'll return to the standard "mongrel"(average size) breed. I mean, if we take any species would we get the same results- I mean, can man breed out a species into a whole new animal- I mean, I don't think man has been able to breed out dogs with all his trying, what makes us think that evolution can do it?
    Reply With Quote  
     

  6. #5  
    WYSIWYG Moderator marnixR's Avatar
    Join Date
    Apr 2007
    Location
    Cardiff, Wales
    Posts
    5,810
    Quote Originally Posted by LAGoff
    I think species remain stable.
    correction : species have the appearance of being stable when viewed from the human time scale - the fact that cats and ibises in pharaonic times are virtually indistinguishable from the present varieties is neither here nor there, since even a few thousand years is a mere blink of an eye in geological terms

    human beings are notoriously bad at applying their gut feeling to items that are not made to the human measure, e.g. the very small (think quantum mechanics) or the very large (geological time or "deep time" as it is sometimes referred to), therefore it is very hard to appreciate at the gut feel level how much time even a few million years encompasses, let alone a few billion

    there's 2 explanations for this appearance of stability :

    one follows from applying punctuated equilibrium - if assumed to be the normal pattern of evolution (an 'if' that is still debated amongst evolutionists), PE postulates that species tend to remain virtually unchanged for relatively long time spans (a case of stabilising natural selection) interspersed with relatively short periods of speciation - if true, this means that you would be lucky to catch a species in the process of speciation

    the other explanation is that a lot of speciation happens without us noticing because many species are not that well studied : there have been many instances of insect or amphibian species that were initially assumed to be single species, until a closer examination (often supported by genetic analysis) showed them to be a group of identical-looking but non-interbreeding sister species
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
    Reply With Quote  
     

  7. #6  
    Forum Cosmic Wizard i_feel_tiredsleepy's Avatar
    Join Date
    Mar 2008
    Location
    Montreal
    Posts
    2,256
    Well as an example that has been observed, wildcats in cities in North America have taken on certain traits of the "American Shorthair" becoming a recognizable breed. In Europe the same cats have become the "European Shorthair" distinct from the American variety but derived from the same origin. Likewise early cats released by American colonist adapted in the forest to become the "Maine Coon", which is the largest of the domestic cat breeds and has a heavy water resistant coat. These three breeds all occured in recent history without direct human interference and derived from relatively similar stock. So, even though the animals may take on the appearance of a stable state, that stable state is a direct result of natural selection, those features were somehow favoured above others to produce that mongrel breed. 3 different environments produced 3 different breeds through natural selection.
    Reply With Quote  
     

  8. #7  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,168
    Quote Originally Posted by LAGoff
    I think species remain stable.
    These remarks are most definitely not meant to be sarcastic:
    I think it depends upon how you define stable.
    I think it depends upon how you define species.

    For example, are we talking about stability of phenotype - roughly how the species looks (and behaves) - or, stability of genotype; the genetic code of the organism. Lingula, a genus of brachiopod extant since the Cambrian, is still around today. It is often held up as an example of stability, being described as a 'living fossil'. But one school of thought claims it has changed in many significant ways since the Cambrian and has only superficially been stable.

    This is just an example of one of the problems you referred to in your opening post. In this case it arises from matters of perspective and definition. Does it mean evolution is faulty? No, it simply means we have not yet learnt all we need/want to learn about the process.
    Reply With Quote  
     

  9. #8  
    Time Lord
    Join Date
    Apr 2008
    Posts
    5,328
    About Cambrian explosion. My chronology may be wrong, but perhaps the eye sparked it? With eyes, you can go after select foods, or prey. Kinda necessary to diversity, that. And also the prey would like predators playing catch up (dinner looks different than breakfast) and Where's Waldo and of course camouflage. Moreover, if the eye expedites getting sustenance there may be slack for frivolous variation.
    Reply With Quote  
     

  10. #9  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,168
    You are thinking, perhaps, of the hypothesis of Andrew Parker, laid out in In The Blink of an Eye, that it was emergence and subsequence evolution of vision that sparked the Cambrian Explosion.

    I could have linked to many sites that review the idea, but I thought it amusing to use this one, from the British Journal of Opthalmology.
    http://www.pubmedcentral.nih.gov/art...?artid=1771979
    Reply With Quote  
     

  11. #10  
    WYSIWYG Moderator marnixR's Avatar
    Join Date
    Apr 2007
    Location
    Cardiff, Wales
    Posts
    5,810
    if the eye was such a powerful driver behind the cambrian explosion, why was it not adopted by most organisms + why are there whole phyla that never evolved an eye ?
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
    Reply With Quote  
     

  12. #11  
    Forum Professor sunshinewarrior's Avatar
    Join Date
    Sep 2007
    Location
    London
    Posts
    1,525
    Hi Lagoff and welcome to the forum.

    My take is slightly different from that of some of the others here, and I may in points even directly contradict them, but I am as committed to evolution as an idea as anybody else here.

    I take a relatively strictly cladistic line on these matters and do not believe, for instance, that a 'phylum' as a concept carves nature at the joints. I take the line, therefore, of Dawkins rather than Gould and Eldridge, in thinking that the alleged explosion during the Cambrian was:

    a) Not as explosive as proponents of punctuated evolution would like to have us believe, and

    b) Not inexplicable in any case - if, say, the atmosphere had been building up to the current high-oxygen one over the previous 3 billion years, then all it would need would be a long-ish threshold period for various lineages to develop ways of taking advantage of these changed circumstances - and the fossil record to start showing them when they developed bodies capable of fossilisation. As it is, the Ediacaran fossil deposits, I think, show that there was a lot of mega-prokaryotic life building up before the Cambrian 'explosion', in any case.

    There may well have been some technological changes that assisted in this apparent blooming, buzzing profusion, like the invention of the eye, or of hard skeletons/body parts and so on, but I doubt if any one of them will prove to have been THE critical element.

    In time, I suspect, the Cambrian 'explosion' will generally be downgraded to 'swell' or not even that, and will not be thought of as a mystery.
    Reply With Quote  
     

  13. #12  
    Forum Ph.D.
    Join Date
    Aug 2006
    Posts
    792
    There are many theories about it just to rattle a few off the top of my head (I have no references!)

    (i) there was no explosion and it was just a point when conditions were right for fossilisation to begin/occur.
    (ii) Oxygen levels rose to such a level (similar to today) that it allowed the development of such organisms which could not have happened before propelled this explosion.
    (iii)Panspermia- that there was some input from outerspace, although what that was is not certain, this is actually supported by the fact that from moon mineral collections, there seems to have been a greater number of meteors hitting the moon around the same time, so it may have provided more organic matter which may somehow propel evolution.
    Reply With Quote  
     

  14. #13  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,168
    Quote Originally Posted by marnixR
    if the eye was such a powerful driver behind the cambrian explosion, why was it not adopted by most organisms + why are there whole phyla that never evolved an eye ?
    Now I am not a supporter of this hypothesis, but I think your argument is a little like a creationist saying, "so if we evolved from monkeys how come there are still monkeys?".
    Apologies for the comparison - I know it is potentially the most insulting one can apply to a solid evolutionist, but I think it is a valid one.
    Reply With Quote  
     

  15. #14  
    Forum Professor sunshinewarrior's Avatar
    Join Date
    Sep 2007
    Location
    London
    Posts
    1,525
    Quote Originally Posted by Ophiolite
    Quote Originally Posted by marnixR
    if the eye was such a powerful driver behind the cambrian explosion, why was it not adopted by most organisms + why are there whole phyla that never evolved an eye ?
    Now I am not a supporter of this hypothesis, but I think your argument is a little like a creationist saying, "so if we evolved from monkeys how come there are still monkeys?".
    Apologies for the comparison - I know it is potentially the most insulting one can apply to a solid evolutionist, but I think it is a valid one.
    Ooooh. It must have hurt having to say that to marnix.

    In any case, to make his point, but differently: while I had never heard of In the Blink of an Eye before this, I would find its presumption, on the face of it, suspicious: the Cambrian period is surely notable not just for the animal life we see, but also for much more by way of fossilisation of large plants and fungi and so on, right? And eyes are entirely irrelevant to them, and in fact are probably deleterious to them as an adaptation that occurs in their environment. So there would be problems, to my mind, to claiming that the technological fix by natural selection was the development of the eye....

    But hey, didn't someone say something along the lines of: "Natural selection is cleverer than you think. In fact, it's cleverer than you can think."?
    Reply With Quote  
     

  16. #15  
    WYSIWYG Moderator marnixR's Avatar
    Join Date
    Apr 2007
    Location
    Cardiff, Wales
    Posts
    5,810
    Quote Originally Posted by sunshinewarrior
    Ooooh. It must have hurt having to say that to marnix.
    nah, i have a thick skin
    although it would be nice if ophi could give himself a token 10-minute self-ban from this forum
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
    Reply With Quote  
     

  17. #16  
    Forum Freshman
    Join Date
    Jun 2008
    Posts
    7
    Thank you for your posts. It's the first time I'm hearing of these ideas. Someone said: "Natural selection is cleverer than you think. In fact, it's cleverer than you can think." I am reminded of the Double-slit Experiment where elementary particles act differently when they "know" they are being watched. This is all I can think of- at this point in my ignorance- to explain the Cambrian Explosion(under 5 million years!) and such things as land mammals developing blow holes in 5(15?) million years.
    Does anybody dispute the time frame of the "explosion"?- i.e. that it was more than 5 million years, or less(could it have been 0 years?)? Also, about whale Evolution, how long was it? I heard 6, but someone said 15 mil.(it's just an example, as I get a kick out of trying to imagine nature taking a land mammal and boring a blow hole into its neck and fusing its feet- again, I gravitate to the Double slit experiment(http://www.youtube.com/watch?v=DfPeprQ7oGc) and how elementary particles have intelligence/awareness("Elementary particles are cleverer than you think....").
    Reply With Quote  
     

  18. #17  
    Forum Professor sunshinewarrior's Avatar
    Join Date
    Sep 2007
    Location
    London
    Posts
    1,525
    Quote Originally Posted by marnixR
    Quote Originally Posted by sunshinewarrior
    Ooooh. It must have hurt having to say that to marnix.
    nah, i have a thick skin
    although it would be nice if ophi could give himself a token 10-minute self-ban from this forum
    Hey - you ought to be showing fellow-Celt solidarity with him... :P

    And cursing us Anglics...
    Reply With Quote  
     

  19. #18  
    WYSIWYG Moderator marnixR's Avatar
    Join Date
    Apr 2007
    Location
    Cardiff, Wales
    Posts
    5,810
    not everyone who lives in wales is welsh
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
    Reply With Quote  
     

  20. #19  
    Forum Professor sunshinewarrior's Avatar
    Join Date
    Sep 2007
    Location
    London
    Posts
    1,525
    Quote Originally Posted by marnixR
    not everyone who lives in wales is welsh
    (I know!)
    Reply With Quote  
     

  21. #20  
    Forum Ph.D.
    Join Date
    Dec 2006
    Location
    Norway
    Posts
    927
    Quote Originally Posted by LAGoff
    Also, about whale Evolution, how long was it? I heard 6, but someone said 15 mil.(it's just an example, as I get a kick out of trying to imagine nature taking a land mammal and boring a blow hole into its neck and fusing its feet- again, I gravitate to the Double slit experiment(http://www.youtube.com/watch?v=DfPeprQ7oGc) and how elementary particles have intelligence/awareness("Elementary particles are cleverer than you think....").
    hehe, you don't need to imagine anything, just take a look at these fossils:





    write the name of each of those fossils into google image search, and get
    pictures like this:

    ambulocetus:



    and basilosaurus:



    notice however that the fossils of the species between basilosaurus and modern whales have still not been found.

    here's also a documentary on whale evolution:
    http://www.pbs.org/wgbh/evolution/li.../l_034_05.html
    when you have eliminated the impossible, whatever remains, however improbable, must be the truth
    A.C Doyle
    Reply With Quote  
     

  22. #21  
    Forum Freshman
    Join Date
    Jun 2008
    Posts
    7
    Seems like it's a matter of 50 million years. That's plenty of time, but look at the diagram: Dalanistes looks like a land mammal and Rhodecetus looks like a whale. Is anybody troubled by this? It's pretty disturbing to me.
    Reply With Quote  
     

  23. #22  
    WYSIWYG Moderator marnixR's Avatar
    Join Date
    Apr 2007
    Location
    Cardiff, Wales
    Posts
    5,810
    i'm not sure if the reconstructions are all that reliable
    e.g. compare the drawing of Ambulocetus with the skeleton in the photograph - the latter clearly shows something not too dissimilar from an otter-like lifestyle, which the drawing doesn't seem to bare out

    as for the transition to an aquatic lifestyle : the critical step from a quadruped to something with fins and flukes definitely took place in the Eocene - it does however not mean that this was the final polished deep-sea diver that we know today (if i remember correctly, fossil remains with evidence of early whales suffering from the bends have been discovered)

    on a further note, the cladogram may give a false impression of completeness and continuity : it does NOT imply that Pakicetus gave rise to Ambulocetus which in turn gave rise to Dalanistes etc.
    cladograms attempt to show the relatedness of sister taxons, which (through mosaic evolution) may have progressed in one way to "whaleness" but not in others - hence one species may have developed an inner ear that is more suited to hearing underwater, while a sister species may have made more progress towards more flipper-like limbs

    the taxa on the cladogram only highlight what the real ancestors of whales may have looked like, it does not imply that they were on the main evolutionary line towards whales
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
    Reply With Quote  
     

  24. #23  
    Time Lord
    Join Date
    Apr 2008
    Posts
    5,328
    Quote Originally Posted by marnixR
    if i remember correctly, fossil remains with evidence of early whales suffering from the bends have been discovered
    Even modern sperm whales suffer from the bends. We examined bones of whales collected over the last century. Chronic harm from nitrogen exploding in the bones appears to be the lot of whales. We haven't checked other tissues yet but one may guess they get a little more than achy going up.

    Link.

    Maybe there's just no way to cheat the bends? What other animal decompresses at such a rate?
    Reply With Quote  
     

  25. #24  
    Forum Ph.D.
    Join Date
    Dec 2006
    Location
    Norway
    Posts
    927
    Quote Originally Posted by LAGoff
    Seems like it's a matter of 50 million years. That's plenty of time, but look at the diagram: Dalanistes looks like a land mammal and Rhodecetus looks like a whale. Is anybody troubled by this? It's pretty disturbing to me.
    beg you pardon?

    rhodecetus is a whale with hind-legs..



    anyways, this wasn't the main reason why dalanistes is believed to be a
    proto-whale. its mainly the shape of the inner earbone, which only
    whales have.
    when you have eliminated the impossible, whatever remains, however improbable, must be the truth
    A.C Doyle
    Reply With Quote  
     

  26. #25 Re: Cambrian Explosion problem 
    Forum Cosmic Wizard spuriousmonkey's Avatar
    Join Date
    May 2005
    Posts
    2,191
    Quote Originally Posted by LAGoff
    Hello,
    I'm slowly coming around to accepting Evolution. I do have two major problems with it though: The Cambrian Explosion/Punctuated Equilibrium problem(i.e. 5 million years or less to evolve these forms),
    I'm afraid you are a bit confused here. I will try to explain why.

    There are nowadays three major sites which represent the so-called cambrian explosion: The Burgess shale of British Colombia, Sirius Passet in Greenland, and the Chengjiang site in China.

    Ghengjiang is dated aroung 525 million years ago, the Sirius passet site is equivalent to that and the Burgess shale is dated at 535-540 million years ago.

    As you can see there is already 15 million years of continuity in the diversity of life, which is similar between but not identical in all three sites. And who knows how many millions of years before that!

    Because the Cambrian explosion was NOT named because this certain set of life evolved rapidly then. It was named explosion because for the first time the fossils appeared.

    Appearance of fossils and evolution of a corresponding species does not equal each other.

    In fact the three sites mentioned are actually extraordinary in quality and only preserved the fossils due to very specific and special circumstances.



    So there was no real explosion. What happened was that conditions became suitable for fossilization. The common ancestor has been put at 590 million years ago (based on molecular clock and phylogenetic reconstructions). That still leaves 65 million years for the diversity to appear. Not 5 million. 65 million years is still equivalent to the extinction of the dinosaurs and the radiation of the modern mammals for instance. A fucking long time.
    "Kill them all and let God sort them out."

    - Arnaud Amalric

    http://spuriousforums.com/index.php
    Reply With Quote  
     

  27. #26  
    WYSIWYG Moderator marnixR's Avatar
    Join Date
    Apr 2007
    Location
    Cardiff, Wales
    Posts
    5,810
    a recent article in Nature suggests that changes in oceanic circulation put an end to widespread anoxic conditions, and thereby made the cambrian explosion possible
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
    Reply With Quote  
     

  28. #27  
    Forum Cosmic Wizard spuriousmonkey's Avatar
    Join Date
    May 2005
    Posts
    2,191
    That's actually quite interesting. I will quote the end of the article here since I kind of know you don't have full access.

    The fact that most Ediacaran fossils have no post-Proterozoic record and that Early Cambrian trace and body fossils appear over only a protracted interval in the Cambrian suggests that the Cambrian fauna did not simply succeed the Ediacaran biota25. This time gap lends substance to the hypothesis that the Ediacaran and Cambrian faunas are separated by an event of mass extinction. Several palaeoclimatic, palaeoenvironmental and palaeoecological reasons can be responsible for mass extinctions in general26. These include catastrophic methane release27, large-scale volcanism (both of which would lead to global warming and hypercapnia), and hydrogen sulphide poisoning due to upwelling euxinic bottom waters. Of these, hydrogen sulphide poisoning is the only process that can account for the observed Early Cambrian Mo isotope signal and provide a plausible explanation for the sudden extinction of the Ediacaran fauna. It is well established that hydrogen sulphide is almost universally toxic to eukaryotic cells in micromolar or higher concentrations22, 28. Increasing oxygenation of the upper ocean and atmosphere following the Marinoan glaciation is thought to have triggered the development of the Ediacaran fauna23, and to have caused destabilization of the oceanic chemocline23. As a consequence, upwelling euxinic bottom water is likely to have rapidly poisoned the Ediacaran fauna.
    It's not so much then that the (pre)Cambrian radiation of species came about due to mass extinction of the existing fauna.

    The cambrian precursors to the species we can find in cambrian deposits had already been radiating as soft bodied species and certain niches, but their chance came probably due to the accidental extinction of the ediacara fauna.

    Similarly mammals were never destined to 'rule' the world were it not for another mass extinction event. The mammalian radiation just became more obvious after the extinction of the dinosaurs. Only careful studies showed that they had already been radiating before that event, but only in certain directions. A mass extinction frees up new environments that can be readily used for speciation events.
    "Kill them all and let God sort them out."

    - Arnaud Amalric

    http://spuriousforums.com/index.php
    Reply With Quote  
     

  29. #28  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,168
    Quote Originally Posted by marnixR
    although it would be nice if ophi could give himself a token 10-minute self-ban from this forum
    I was away all weekend. Will that do?
    Reply With Quote  
     

  30. #29  
    WYSIWYG Moderator marnixR's Avatar
    Join Date
    Apr 2007
    Location
    Cardiff, Wales
    Posts
    5,810
    hmm - i'll let it pass for once
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
    Reply With Quote  
     

Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •