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Author | Topic: Is the ‘missing link’ argument outdated? | |||||||||||||||||||||||||||
pink sasquatch Member (Idle past 6023 days) Posts: 1567 Joined: |
I’ve noticed that many creationists seem to demand a continuous fossil record of transitional forms (‘missing links’) as evidence of evolution, an example:
http://EvC Forum: Is Ape/Human Common Ancestory Enough? -->EvC Forum: Is Ape/Human Common Ancestory Enough? It would seem that recent genetic discoveries would refute the idea that we should definitely see a smooth, continuous record of morphological variants. The genetic evidence shows single genetic changes can result in drastic morphological differences — likely fitting somewhere in between ‘micro’ and ‘macro’ evolution. One study demonstrated that humans (only) carry a mutation in a jaw-specific muscle gene — explaining why non-human primates and other predators have a ten-fold greater jaw strength than us puny humans.
http://www.ncbi.nlm.nih.gov/entrez/...#1 The researchers speculate that the loss of jaw-muscle strength/size released constraints on skull size, allowing for more space for the brain to develop (humans simultaneously got weaker physically and stronger mentally). If this seems absurd, keep in mind that reconstructive surgery in humans can alter skull shape if jaw muscles are not attached in the same place — similar skull changes are seen in animal models following surgery. The suggested ('molecular clock') timing of the mutation matches timing of skull differences in the fossil record (although you’d have to believe the dating procedures). Suggested here is a leap in morphology, essentially in one generation. If true, there should be no expectation to see a transitional skull someplace between the pre- and post- mutation morphology. Other drastic (possibly single-generation) changes have been found; one involves the near gain/loss of hind-limbs through alteration of a gene promoter:
http://www.ncbi.nlm.nih.gov/entrez/...#2 Again, the genetic change results in long or short (near absent) limbs — there is no reason to expect to find medium-length limbs if this is the only genetic change. I think it is easy to envision other mechanisms that could drastically effect an organism, such as growth hormone related mutation that drastically increases or decreases the overall size of an organism, likely with secondary changes. In some cases (as in the one about the skull, above) a drastic change in morphology or function could provide selective pressure for other adaptations. Should evolutionists continue to defend the transitional fossil record to creationists who claim that there are gaps? Why not explain that we expect some gaps? that there is strong scientific evidence to support them? {Shortened display form of 2 URLs, to restore page width to normal - AM} This message has been edited by Adminnemooseus, 06-23-2004 01:21 AM
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AdminAsgara Administrator (Idle past 2303 days) Posts: 2073 From: The Universe Joined: |
Thread moved here from the Proposed New Topics forum.
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Loudmouth Inactive Member |
Good post. You should also realize that there is not a biological/geological "law" that requires the fossilization of every species that ever lived. In fact, given the lack of fossils for organisms that have become extinct in the last 200 years really pushes home this fact. Passenger pigeons are a perfect example. They numbered in the billions in North America until they went extinct about a hundred years ago. Guess what, no fossils of passenger pigeons.
You can also factor in the amount of land we have actually scoured for fossils. I wouldn't be surprised to hear a geologist claim that only 0.0001% of the earth has been searched for fossils. It's not so much that there are "missing" links. A more accurate portrayal is that they are "yet to be found" links. And yet another factor is subduction. Old land is destroyed while new land is created. Right now there are fossils being pushed back into the mantle where they are melted into magma. Just to sum up: 1. Fossilization is rare. 2. We haven't even scratched the surface in our search for new fossil species. 3. There are mechanisms that destroy fossils.
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pink sasquatch Member (Idle past 6023 days) Posts: 1567 Joined: |
Loudmouth - thanks for the geological input - since I tend to primarily think in biological terms, it is good to have evidence from another field.
I posted the topic because in other forums evolutionists (presumably) were trying to convince ID/creationists that the fossil record contains all transitional forms, even if they haven't been found yet. Creationists were taking the gaps as proof of creation (however incorrect that leap to "proof" is...) I think a more scientific argument would be: both biological and geological evidence suggests that there will be gaps, and here's some evidence... I enjoyed the passenger pigeon example - I wonder how many other species that humans have witnessed with their own eyes have never been found in fossilized form...
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Loudmouth Inactive Member |
quote: Exactly. On top of the fossil evidence is the corroboration between genetics and the fossil record. If the fossil record were a jumbled mess laid down by a global flood then we would not expect phylogenies based on the fossil record to match phylogenies based on DNA. The fact that we a correlation between DNA and the fossil record adds credence to both. Gaps or no gaps, there is no denying common ancestory.
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MrHambre Member (Idle past 1393 days) Posts: 1495 From: Framingham, MA, USA Joined: |
Creationists who use the 'missing link' argument, ironically, assume beforehand that the change we see in the fossil record is driven by heredity. In fact, the fossil record is really just a reflection of the change in our biosphere over the past few billion years. Realistically, though, our view of the fossil record has changed dramatically since Darwin's day. I always use the image of those flip-movies I make for my kids on note pads: the Spy vs. Spy guys tossing a bomb back and forth, a pole vaulter, whatever. We 'see' motion through the quick succession of frames.
In the old view (and for most contemporary creationists), the flip-movie of the fossil record has a species at the left of the page, and each page represents a very slight shift to the right. Over thousands of pages, the species finally make it to the right of the page (our modern species). The action should be smooth, the transitions seamless. Even if we only have ten percent of these pages, the changes should be easily reconstructed. Unfortunately, the fossil record does not reflect this: the vast majority of fossils don't reflect such perfectly gradual transitions from the previous species. The way we see the fossil record post-Gould is this: the species remains in the same spot at the left of the page for hundreds of pages, then there are ten or so pages where it shifts to the center. Then it stays in the center of the page for hundreds more pages, before shifting to the extreme right of the page in ten or so frames. Thereafter it remains at the right of the page. This makes for abrupt shifts when we flip the movie, and the quick transitions go by too quickly for our eyes. Now if we only have ten percent of the frames, the chances that we'll see any of those quick transitions is statistically slim. So the missing links are that way for a reason, and the criticism of the fossil record on that basis doesn't reflect well on the people who continue to raise the point. regards,Esteban Hambre
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NosyNed Member Posts: 8996 From: Canada Joined: |
But some of those few frames are found in spite of the difficulties.
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Cthulhu Member (Idle past 5852 days) Posts: 273 From: Roe Dyelin Joined: |
Another problem is that the discoveries of many transitional fossils aren't reported in major news outlets, because the general public really doesn't care about it. It doesn't sell. This leads many people, who don't read the more scientifically oriented magazines, to assume that no transitional fossils have been found.
Ia! Cthulhu fhtagn! Proudly attempting to Google-Bomb Kent "The Idiot" Hovind's website
Idiot
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jar Member (Idle past 394 days) Posts: 34026 From: Texas!! Joined: |
One important thing to remember is that both models are likely correct. If Natural Selection is right, we should see some things that show almost no change over time, some things that gradually change over time and others where there is a rapid change.
And that is pretty much what is seen. It's not one or the other, it is what happened within the population or period that you are examining. We know that the outside forces and conditions have varied. There have been periods of major local change, major global change, minor change, long periods of stability and even environments that have remained almost identical over most of history. Why should the record found in fossils be any different? Aslan is not a Tame Lion
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MarkAustin Member (Idle past 3815 days) Posts: 122 From: London., UK Joined: |
quote: It is worth pointing out that Gould is not considered a major thinker on evolutionary theory. Ernst Meyer had already done most of the work on punctuated equilibrium, and the majority view is that, while species do remain stable for extended periods, punctuated equilibrium is not the only, or even the dominant, mode of evolution as Gould postulates. In fact, Human evolution shows this. From Australopithecus to Homo Sapiens, the record shows not a series of jumps but a relatively smooth transition, as illustrated by the occasional confusions about where a particular fossil fits in the record (for example confusion about fossils on the boundary between Australopithecus and Homo Habilis). Edited to add example in brackets. This message has been edited by MarkAustin, 08-13-2004 02:41 AM For Whigs admit no force but argument.
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MrHambre Member (Idle past 1393 days) Posts: 1495 From: Framingham, MA, USA Joined: |
I'm not a big Gould fan either. I think Daniel Dennett did a job on Gould's complaints against "panadaptationism" in the chapter of Darwin's Dangerous Idea dedicated to Gould's 'spandrels' essay. Anyone who likes a savage debate should be impressed by Dawkins's "Puncturing Punctuationism" chapter in The Blind Watchmaker, in which he disputes not the validity but rather the revolutionary nature of Gould's pet theory. It's true that Gould took credit for ideas that had been aired long before, overstated his case, and gave creationists a lot of fodder.
However, Gould is to be praised for pointing out that our mistaken expectations concerning the fossil record are what fuels the "missing link" argument. As Ned asserted, even the statistical improbability of finding a fossil of one of the rare 'transition' species hasn't stopped paleontologists from doing so on several occasions. I'm no expert on human fossils, but it's hard to deny that there are precious few of them (especially compared to such groups as trilobites, which were Eldredge's specialty), certainly to be expected for a recent transition that took place over a mere few million years. Therefore, our evidence of human ancestry is based on the same fortuitous breaks to which Ned refers. regards,Esteban Hambre
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