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Author Topic:   Does O. recapitulate P. or doesn't it?
tomato
Member (Idle past 2465 days)
Posts: 39
Joined: 10-11-2009


Message 1 of 8 (531447)
10-18-2009 12:36 AM


I have read in some places, such as the talkorigins Website, that Evolutionists reject not only Haeckel's falsified drawings, but his entire recapitulation theory as well.

But I have read at other places that:

Ēš horse embryos have three toes, just like their ancestors.
Ēš bird embryos have claws where their wings later develop, just like their reptilian ancestors.
Ēš bird embryos grow through a phase in which their pelvic bones are like those of the Archaeopteryx.
Ēš all vertebrate embryos go through a phase in which they have a notochord in place of a backbone, just like our invertebrate ancestors.
Ēš whale embryos possess teeth, legs, and hair, just like their land-dwelling ancestors.
Ēš elephant embryos possess an extra pair of tusks, just like their Oligocene ancestors.
Ēš human embryos possess tails, just like our simian ancestors.

If this doesn't show that Haeckel was right, what DOES it show?

Edited by tomato, : No reason given.


Replies to this message:
 Message 3 by Meldinoor, posted 10-18-2009 1:05 AM tomato has not yet responded
 Message 4 by Dr Adequate, posted 10-18-2009 6:37 AM tomato has responded

    
AdminNosy
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Message 2 of 8 (531449)
10-18-2009 12:39 AM


Thread Copied from Proposed New Topics Forum
Thread copied here from the Does O. recapitulate P. or doesn't it? thread in the Proposed New Topics forum.
  
Meldinoor
Member (Idle past 2971 days)
Posts: 400
From: Colorado, USA
Joined: 02-16-2009


(2)
Message 3 of 8 (531450)
10-18-2009 1:05 AM
Reply to: Message 1 by tomato
10-18-2009 12:36 AM


Yes and no.

Recapitulation theory, as Haeckel imagined it, has been rejected by science. Haeckel believed that each embryo went through clearly defined stages of evolution, resembling a fish, a reptile, and so on, gradually moving through the evolutionary history of some species. This view was not accurate.

However, you can see many clues for a species evolutionary history in the development of the embryo. As you have rightly pointed out, many features that evolved early on are also the first to develop in the embryo. And many modern features develop from what resembles more ancient features in the embryo (like pharyngeal arches, which resemble gill slits).

The reason for this is fairly obvious. We know that evolution changes the morphology of a species. Humans don't change much after embryonal development, and neither do most tetrapods for that matter. So what evolution is really modifying is the development of the embryo. Since evolution isn't an intelligent designer, it won't go back to the drawing board everytime a species evolves a new function. Instead, evolution alters structures that the organism already has. If embryos are already developing gill slits, it's not difficult for modifications to turn those developing gill slits into something else useful.

Evolution doesn't care as much about what stages the embryo passes through as it does for the final product. If natural selection favored human ancestors who lost their tails, it only selected for the end product. If the embryo stayed true to the mold set up by many earlier generations with tails, but then lost it before it completed development, natural selection would still favor it.

Now for the disclaimer. I'm not a biologist, so I'm sure our resident scientists will explain it better for you, or point out inaccuracies in my reply. But this is my impression of how things work.

Respectfully,

-Meldinoor

Edited by Meldinoor, : Corrected typo


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Dr Adequate
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Posts: 16095
Joined: 07-20-2006


Message 4 of 8 (531471)
10-18-2009 6:37 AM
Reply to: Message 1 by tomato
10-18-2009 12:36 AM


This is a good question. Biologists themselves get confused about this.

The prediction of the theory of evolution is as follows

If an embryo develops, and then loses, some significant feature during its embryological development, then that feature must be ancestral (as confirmed by other considerations, such as the fossil record, morphology, molecular phylogeny, and so forth).

Note that this is not at all what Haeckel said.

Edited by Dr Adequate, : No reason given.


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 Message 1 by tomato, posted 10-18-2009 12:36 AM tomato has responded

Replies to this message:
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 Message 6 by Blue Jay, posted 10-18-2009 12:56 PM Dr Adequate has responded

  
tomato
Member (Idle past 2465 days)
Posts: 39
Joined: 10-11-2009


Message 5 of 8 (531476)
10-18-2009 7:04 AM
Reply to: Message 4 by Dr Adequate
10-18-2009 6:37 AM


I guess I score 7 out of 7, then.
All of my examples meet that requirement.
This message is a reply to:
 Message 4 by Dr Adequate, posted 10-18-2009 6:37 AM Dr Adequate has responded

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Blue Jay
Member (Idle past 860 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 6 of 8 (531531)
10-18-2009 12:56 PM
Reply to: Message 4 by Dr Adequate
10-18-2009 6:37 AM


Hi, Dr A.

Dr Adequate writes:

The prediction of the theory of evolution is as follows

If an embryo develops, and then loses, some significant feature during its embryological development, then that feature must be ancestral (as confirmed by other considerations, such as the fossil record, morphology, molecular phylogeny, and so forth).

I don't think this statement is entirely accurate: it's possible for a new feature to evolve for a short-term benefit during some stage of embryological development (I can't think of any examples in which this is the case, but it is entirely possible).

I'm worried about the false dichotomy your statement seems to be setting up: if we ever do find an ephemeral embryological feature that isn't ancestral, ToE could still explain its evolution.


-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.


This message is a reply to:
 Message 4 by Dr Adequate, posted 10-18-2009 6:37 AM Dr Adequate has responded

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Dr Adequate
Member
Posts: 16095
Joined: 07-20-2006


Message 7 of 8 (531589)
10-19-2009 12:31 AM
Reply to: Message 6 by Blue Jay
10-18-2009 12:56 PM


I don't think this statement is entirely accurate: it's possible for a new feature to evolve for a short-term benefit during some stage of embryological development (I can't think of any examples in which this is the case ...

The egg tooth.

I should have included the word "useless" somewhere in my statement.


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Dr Adequate
Member
Posts: 16095
Joined: 07-20-2006


Message 8 of 8 (531591)
10-19-2009 12:37 AM
Reply to: Message 5 by tomato
10-18-2009 7:04 AM


I guess I score 7 out of 7, then.
All of my examples meet that requirement.

They do indeed. Though I think it is Darwin and not you who gets 7 out of 7.

But yes, that's what the theory of evolution tells us about embryology.

Note that it divides events into those that can happen and those that can't, not those that must happen and those that mustn't. For example, the theory says that humans can grow a coat of fur and then lose it as an embryo. (Which we do.) It also says that we can't grow and then lose feathers. (We don't.) But it also says that we can grow and lose scales, what with being descended from fish. And we don't. It doesn't mandate that we should recapitulate ancestral forms, it says that we can only recapitulate ancestral forms.


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