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| LAGoff |
 Posted: Mon Jun 02, 2008 10:48 pm Post subject: Cambrian Explosion problem |
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Forum Freshman
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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 |
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| marnixR |
| Posted: Tue Jun 03, 2008 12:19 am Post subject: |
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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)
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| Ophiolite |
| Posted: Tue Jun 03, 2008 1:25 am Post subject: |
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Forum Radioactive Isotope
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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.
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| LAGoff |
| Posted: Tue Jun 03, 2008 8:54 am Post subject: |
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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? |
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| marnixR |
| Posted: Tue Jun 03, 2008 9:17 am Post subject: |
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| LAGoff wrote: |
| 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
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| i_feel_tiredsleepy |
| Posted: Tue Jun 03, 2008 9:27 am Post subject: |
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| 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. |
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| Ophiolite |
| Posted: Wed Jun 04, 2008 1:05 am Post subject: |
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Forum Radioactive Isotope
Joined: 25 Jul 2005
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| LAGoff wrote: |
| 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.
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| Pong |
| Posted: Wed Jun 04, 2008 3:54 am Post subject: |
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| 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. |
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| Ophiolite |
| Posted: Wed Jun 04, 2008 4:19 am Post subject: |
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Forum Radioactive Isotope
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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/articlerender.fcgi?artid=1771979
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| marnixR |
| Posted: Wed Jun 04, 2008 5:06 am Post subject: |
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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 ?
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| sunshinewarrior |
| Posted: Wed Jun 04, 2008 6:12 am Post subject: |
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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. |
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| Robbie |
| Posted: Wed Jun 04, 2008 6:49 am Post subject: |
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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.
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| Ophiolite |
| Posted: Wed Jun 04, 2008 8:42 am Post subject: |
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Forum Radioactive Isotope
Joined: 25 Jul 2005
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| marnixR wrote: |
| 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.
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| sunshinewarrior |
| Posted: Wed Jun 04, 2008 8:51 am Post subject: |
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| Ophiolite wrote: |
| marnixR wrote: |
| 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."? |
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| marnixR |
| Posted: Wed Jun 04, 2008 9:00 am Post subject: |
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| sunshinewarrior wrote: |
| 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 
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