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Author | Topic: All species are transitional | |||||||||||||||||||||||
JustinC Member (Idle past 4844 days) Posts: 624 From: Pittsburgh, PA, USA Joined: |
This is kindof a trivial point, but it a creature dies without breeding then it isn't transitional.
Or, if we are using "species" as a valid classification then a species that goes extinct, without some of it's populations evolving into another species, is not transitional.
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JustinC Member (Idle past 4844 days) Posts: 624 From: Pittsburgh, PA, USA Joined: |
I don't know if I agree. Where did you get your definition of transitional species? I always considered a transitional to be a direct link between two species. So it would have to fit in the timeline between the two species and share features of the oldest species while showing characteristics of the later one.
I wouldn't say the platypus is transitional, I would say it is closely related (atleast morphologically) to the the transitional species between placental mammals and non-mammal therapsids.
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JustinC Member (Idle past 4844 days) Posts: 624 From: Pittsburgh, PA, USA Joined: |
quote:I'd say they are using a very loose definition of transitional species. Transition means to change from one form to another. So if archeaopteryx wasn't a species in the lineage going from a species of theropod dinosaur to modern birds, it wasn't a transitional species between the two. It may be an offshoot of a transitional. I think there is a difference between showing characteristics between two groups and being a transitional between two groups. The former would blur the distinction between groups, maybe even showing the dichotomy wasn't warrented. The latter would show they are related by a descent-ancestor relation.
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JustinC Member (Idle past 4844 days) Posts: 624 From: Pittsburgh, PA, USA Joined: |
Well, nothing is certain in science. So I would say there no transitional fossils "known".
We hypothesize that there should be a transitional between two species, and we find likely canidates for this transitional. There is much utility in defining transitionals the way you do. The creatures you are referring to show there are no "kinds" in nature. But should be redefine what "transition" means in order to say we "know" there are transitionals? But if I'm looking for the evolutionary link (a transitional) between therapsids and placentals, and you show me a platypus I'd be a little incredulous. Also, i've had this discussion with my Evo professor so I know I'm in the "wrong" compared to the scientific consensus. In the end it's just semantics. It makes more sense, to me, to define transitional the way I did.
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JustinC Member (Idle past 4844 days) Posts: 624 From: Pittsburgh, PA, USA Joined: |
quote:The thing is I'm not making up my own definition. That is what transitional means to 99% of the public. When a layperson hears that there is a transitional between two species, they think there is an evolutionary link. This is what creationists think the word means, and I think this causes much confusion when debating them. When a creationist says there are no transitional fossils, aren't they just saying there are no missing links? And isn't it disingenuous to tell them we have have transitionals when we are using a different definition than them? It seems absurd to say there is a transitional species between chimpanzees and humans since we are contemporaries known not to be in an ancestor-descendent relationship. Doesn't your definition basically say there are transitionals between any two species we pick? What is the utility in that? And interestingly enough, I never heard my professor once use the word transitional. Nor is it found anywhere in my text book, Evolution by Mark Ridley. Is it even used within formal evolutionary biology?
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JustinC Member (Idle past 4844 days) Posts: 624 From: Pittsburgh, PA, USA Joined: |
I just looked through "What Evolution Is" by Mayr, and he also doesn't mention transitional species. At best, he mentions "missing links showing the transition between two taxon" or something to that effect.
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JustinC Member (Idle past 4844 days) Posts: 624 From: Pittsburgh, PA, USA Joined: |
I, personally, have never heard an expert use the word.
I've read a couple of Evo textbooks as well. They mention missing links forming transitions between two species. That is the closest I have seen, and it uses transition in normal sense.
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JustinC Member (Idle past 4844 days) Posts: 624 From: Pittsburgh, PA, USA Joined: |
I just read a little bit of the FAQ of transitionals from Talk Origins.
Here's what they have to say:
"General lineage":
I'll concede that it is too stringent a definition to say that a transitional must be directly ancestral.This is a sequence of similar genera or families, linking an older group to a very different younger group. Each step in the sequence consists of some fossils that represent a certain genus or family, and the whole sequence often covers a span of tens of millions of years. A lineage like this shows obvious morphological intermediates for every major structural change, and the fossils occur roughly (but often not exactly) in the expected order. Usually there are still gaps between each of the groups -- few or none of the speciation events are preserved. Sometimes the individual specimens are not thought to be directly ancestral to the next-youngest fossils (i.e., they may be "cousins" or "uncles" rather than "parents"). However, they are assumed to be closely related to the actual ancestor, since they have intermediate morphology compared to the next-oldest and next-youngest "links". The major point of these general lineages is that animals with intermediate morphology existed at the appropriate times, and thus that the transitions from the proposed ancestors are fully plausible. General lineages are known for almost all modern groups of vertebrates, and make up the bulk of this FAQ. But the main problem I have with your definition is that it doesn't take time into account. Notice TalkOrigins says:
quote:It just doesn't make sense to call the platypus a transitional species since there is no evidence of it existing during the therapsid (cynodont specifically)-mammal transition period (i.e., before 245 million years ago).
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JustinC Member (Idle past 4844 days) Posts: 624 From: Pittsburgh, PA, USA Joined: |
quote:I'd assume that the TalkOrigins site is written for the layperson, and they use "transitional" as synonomous with "possible missing link", which is much closer to the definition I gave than yours. I have yet to see a site that gives a definition so broad that the platypus is considered a transitional. This message has been edited by JustinC, 10-06-2005 11:33 AM
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JustinC Member (Idle past 4844 days) Posts: 624 From: Pittsburgh, PA, USA Joined: |
It would destroy every model of human evolution to date. Even so, the time frame is still short evolutionary speaking, so I don't think it would be that devestating to the evolutionary paradigm as a whole.
Now, if humans were found in fossils dating before the Triassic I think that would be devestating. This message has been edited by JustinC, 10-06-2005 11:37 AM
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JustinC Member (Idle past 4844 days) Posts: 624 From: Pittsburgh, PA, USA Joined: |
I meant that it really wouldn't be pushing the date back that far, in terms of the evolutionary time scale. You'd push it from about 200,000 years ago to 4 million years ago. There were mammals, more specificaly primates, 4mya so it could just indicate we evolved from a different lineage of which we have no knowledge.
If you push it back 300 mya, as jar said, we'd be in trouble in terms of our view of common descent. The reason being is that there weren't any official "mammals" back then, and therefore no primates. This wouldn't make sense in terms of common descent since we are most related to primates and should therefore have a relatively synchronous origin in the record (by synchronous I mean within the range of 30-50mya or so). It would really hurt the common descent paradigm if organisms just showed up randomly in the fossil record, i.e., humans 300mya, chimps 2.5mya, lizards 200,000 ya, etc.
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JustinC Member (Idle past 4844 days) Posts: 624 From: Pittsburgh, PA, USA Joined: |
[deleted]
This message has been edited by JustinC, 10-06-2005 05:00 PM
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JustinC Member (Idle past 4844 days) Posts: 624 From: Pittsburgh, PA, USA Joined: |
To wrap this up, I'll concede that my definition was too stringent (which I did a few posts back).
My only concern with your definition is that it didn't mention chronology, which I think is a very important factor when we call something a transitional. You're definition would seem to show that a platypus is a transitional in the cynodont-mammal transition, which would lead me to believe there is something wrong with your definition. I'll also concede that my original statement "if a species goes extinct without another species budding off it, then it is not transitional" is wrong. The reason being is that this species can be very closely related to an animal that is a "missing link" in an ancestor-descendent relationship. So even though it is not the missing link, it could be considered transitional in that it shows intermediate morphology and existed in the correct time period. Transitional is intimately linked to the idea of missing links and really can't be defined otherwise. Any objections to the above? This message has been edited by JustinC, 10-06-2005 05:10 PM
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