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Author Topic:   Wombat Pouch
Straggler
Member
Posts: 10284
From: London England
Joined: 09-30-2006


Message 16 of 85 (615574)
05-14-2011 12:07 PM
Reply to: Message 15 by jar
05-14-2011 11:59 AM


Re: passing the plate
jar writes:

So would the genes from the mothers who just happened to have a pouch opening that protected the infant more get passed on?

Of course. But how does that get translated into graduated change in orientation?

That is the (possibly flawed) question.

We know why wombat pouches face the other way. the question is how did this come about via gradual evolutionary change given that all marsupials are reckoned to be derived from a common ancestor.


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jar
Member
Posts: 30934
From: Texas!!
Joined: 04-20-2004


Message 17 of 85 (615576)
05-14-2011 12:13 PM
Reply to: Message 16 by Straggler
05-14-2011 12:07 PM


Re: passing the plate
So if because of errors some mothers pouch openings were lower would those mothers children have a greater likelihood of living long enough to pass on their genes?


Anyone so limited that they can only spell a word one way is severely handicapped!
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Straggler
Member
Posts: 10284
From: London England
Joined: 09-30-2006


Message 18 of 85 (615578)
05-14-2011 12:17 PM
Reply to: Message 17 by jar
05-14-2011 12:13 PM


Re: passing the plate
So your answer to the question is that the pouch opening gradually moved downwards?
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jar
Member
Posts: 30934
From: Texas!!
Joined: 04-20-2004


Message 19 of 85 (615580)
05-14-2011 12:20 PM
Reply to: Message 18 by Straggler
05-14-2011 12:17 PM


Re: passing the plate
I'm not sure of the direction or how rapidly it happened. But my answer would be that it happened over time.


Anyone so limited that they can only spell a word one way is severely handicapped!
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Percy
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Posts: 18309
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.7


Message 20 of 85 (615584)
05-14-2011 12:44 PM
Reply to: Message 19 by jar
05-14-2011 12:20 PM


Re: passing the plate
I think you've got the answer.

The way I've been looking at this is by imagining the pouch as a four-sided flap of skin attached on three sides. In the kangaroo the top side of the flap is free, and in the wombat the bottom side. How could which side of the flap is free change gradually over time from top to bottom, or vice-versa if bottom-side-free came first. Seems impossible.

But that's the wrong way to look at it. The pouch is actually a flap of skin attached on four sides with an opening. In kangaroos the opening is at the top, in wombats at the bottom. Whichever direction the change occurred, it happened through a gradual change in the position of the pouch opening.

--Percy

Edited by Percy, : Grammar.


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jar
Member
Posts: 30934
From: Texas!!
Joined: 04-20-2004


Message 21 of 85 (615588)
05-14-2011 1:01 PM
Reply to: Message 20 by Percy
05-14-2011 12:44 PM


Re: passing the plate
The change does not have to be major or even directional. In the case of wombats if one had a opening on either side it would give a reproductive advantage to their young. If the slot was at the bottom there would be again an increased reproductive advantage.

It really is just a matter of time and passing on them genes.


Anyone so limited that they can only spell a word one way is severely handicapped!
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Dr Adequate
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Posts: 16085
Joined: 07-20-2006
Member Rating: 10.0


Message 22 of 85 (615595)
05-14-2011 1:52 PM
Reply to: Message 1 by InGodITrust
05-13-2011 3:25 PM


Backwards-facing pouches are not unique to wombats, they are also found in such species as quolls, Tasmanian devils, and koalas. So it's not particularly an adaptation to burrowing, though it might have come in handy.

Nor is it clear which form is basal. Why shouldn't the kangaroo/wallaby type pouch be the adaptation? That vertical posture and all that bouncing up and down might have made it useful.

Obviously the pouch didn't just turn around. A plausible intermediate form would involve both an anterior and a posterior flap. Then whichever one of them was basal got smaller, eventually disappearing altogether, while the other one got bigger and took over its function. (This supposes that the difference between the pouches has been explained right and that I'm visualizing it right.)


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Dr Adequate
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Posts: 16085
Joined: 07-20-2006
Member Rating: 10.0


Message 23 of 85 (615596)
05-14-2011 1:53 PM
Reply to: Message 10 by frako
05-14-2011 10:34 AM


i dont think the "rotation" of the pouch had to be gradual, it could have been a single mutation like when people get a mutation that makes their legs face backwards.

Does this actually happen?


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ZenMonkey
Member (Idle past 2588 days)
Posts: 428
From: Portland, OR USA
Joined: 09-25-2009


Message 24 of 85 (615601)
05-14-2011 2:53 PM
Reply to: Message 22 by Dr Adequate
05-14-2011 1:52 PM


Dr Adequate writes:

Obviously the pouch didn't just turn around. A plausible intermediate form would involve both an anterior and a posterior flap. Then whichever one of them was basal got smaller, eventually disappearing altogether, while the other one got bigger and took over its function. (This supposes that the difference between the pouches has been explained right and that I'm visualizing it right.)

I think that perhaps this is the problem that Percy initially envisioned. What kind of intermediate steps are available for such a shift (shall we say) from a pouch that opens in the front to one that opens in the rear? I can only come up with either an opening at the side that moves backward, or two openings, one that the front and one at the rear.

Or is the whole notion of the necessity of a shift or rotation really a question that only a creationist would ask?

Of course, it could be that the common ancestor had neither a definitive front or rear pouch, and then two subsequent marsupial lines split off, each developing its own arrangement. But I have absolutely no knowledge of marsupial cladistics to know if there's any basis for this supposition.

The difference between me and a creationist being that I admit up front that this is just a supposition and not meant to be a statement of fact.


Your beliefs do not effect reality and evidently reality does not effect your beliefs.
-Theodoric

Reality has a well-known liberal bias.
-Steven Colbert

I never meant to say that the Conservatives are generally stupid. I meant to say that stupid people are generally Conservative. I believe that is so obviously and universally admitted a principle that I hardly think any gentleman will deny it.
- John Stuart Mill


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InGodITrust
Member (Idle past 2398 days)
Posts: 53
From: Reno, Nevada, USA
Joined: 05-02-2009


Message 25 of 85 (615615)
05-14-2011 7:05 PM
Reply to: Message 24 by ZenMonkey
05-14-2011 2:53 PM


Well, if the koala has a pouch that does not open on an end, but opens somewhere in between the ends, this pretty much kills the creationist argument, I have to admit. When confronted with features or behaviors of a particular animal that were hard to fathom being the result of natural selection, we know that Darwin often pointed out some other creature that seemed to show an intermediate step, such as the species of bees that did not build perfectly hexagonal chambers in their hives, but was approaching it. The koala pouch might fit that bill.

It still seems weird, though, that a pouch that opened in the middle would be superior to one opening on the end, and give the animal an advantage. I guess when the offspring were tiny, it wouldn't make a differnce to them; any pouch arrangement would keep them warm and covered. But when they grew bigger, it seems like a center-opening pouch would be less secure. But even to an animal that didn't burrow, but just moved through heavy brush, a center-opening pouch might be better that a front opener.

Like Percy discribed, I at first envisioned a pouch as a four-sided flap that was attached on three sides, so that if the opening reversed orientation by steps, it would "rotate." So if it rotated 90 degrees, the opening might aim right at a hind leg. This way of turning the pouch around doesn't make much sense; if one genetic mutation caused the pouch to rotate say 10 degrees, it's hard to imagine a benefit.

And if one genetic mutation turned the pouch 180, wouldn't other simultaneous mutations be needed to make the new arrangment go. For example, would the new borns have the instict to find their way into the pouch, if it were suddenly reversed?

So a lateral opening moving in steps from one end of the pouch to the other (no matter which direction) seems to fit best with natural selection.

Thanks people. I'll come back when I find something that I think might cast some doubt on the TOE.

IGIT

Edited by InGodITrust, : No reason given.

Edited by InGodITrust, : No reason given.

Edited by InGodITrust, : spelling


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frako
Member
Posts: 2813
From: slovenija
Joined: 09-04-2010


Message 26 of 85 (615623)
05-14-2011 8:08 PM
Reply to: Message 23 by Dr Adequate
05-14-2011 1:53 PM


Does this actually happen?

Well usually only some joints rarely the whole legs joints like the knee bending forwards instead of backwards

http://www.oddee.com/item_92015.aspx


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Wounded King
Member (Idle past 2172 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 27 of 85 (615633)
05-15-2011 4:53 AM
Reply to: Message 25 by InGodITrust
05-14-2011 7:05 PM


So a lateral opening moving in steps from one end of the pouch to the other (no matter which direction) seems to fit best with natural selection.

I think you are making the mistake of assuming that either end opening configuration is the primitive state and that the alternative needs to therefore be superior to it.

If you look at the Dasyurids, often considered a more primitive clade of marsupials, many have a very rudimentary pouch which is little more than a circular fold of skin covering the teats (Wooley et al., 2002). What we are seeing in such cases rather than an intermediate step between a backward and forward facing pouch is more likely the ancestral condition from which both of those states are derived.

It still seems weird, though, that a pouch that opened in the middle would be superior to one opening on the end, and give the animal an advantage.

If these were the first forms of pouch to arise then all such rudimentary pouches need to be is better than no pouch at all.

TTFN,

WK


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InGodITrust
Member (Idle past 2398 days)
Posts: 53
From: Reno, Nevada, USA
Joined: 05-02-2009


Message 28 of 85 (615667)
05-15-2011 2:50 PM
Reply to: Message 27 by Wounded King
05-15-2011 4:53 AM


Good point, WK. You've given a clearer picture of how natural selection could work to shape the various marsupial pouches. Thanks.
IGIT
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Meddle
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Posts: 166
From: Scotland
Joined: 05-08-2006


Message 29 of 85 (615699)
05-15-2011 8:36 PM
Reply to: Message 1 by InGodITrust
05-13-2011 3:25 PM


If an intelligent designer viewed the pouch as problematic, why did it not give the wombat a placenta instead?
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Robert Byers
Member (Idle past 2446 days)
Posts: 640
From: Toronto,canada
Joined: 02-06-2004


Message 30 of 85 (615901)
05-18-2011 3:47 AM
Reply to: Message 1 by InGodITrust
05-13-2011 3:25 PM


InGodITrust writes:

One of the best creationist arguments I have heard concerns the "backward" pouch of the wombat. Opposite to most marsupial pouches, the wombat's opens to the rear, which is valuable to it, as a burrowing animal, for keeping dirt out of the pouch. But how could the pouch turn around by natural selction?

When I first heard about this problem, I thought that the answer that would satisfy natural selection would be that the wobat evolved its pouch seperatly from marsupials that evolved front-opening pouches. But I just saw a TV show that said all of the world's marsupials have a common ancestor: a rat-like animal that lived in China.

So is there a well known solution to this probalem that I have missed? I searched the web and the EVC forums for discussion on it, but found none. Could the pouch have flipped around in one fell swoop, with a single genetic mutation? If so, wouldn't other simultateous mutations have had to occur to make the new pouch work? And if the pouch transitioned in a series of small steps, what would that have looked like?

IGIT

YEC here. I insist marsupials are just placentals who in some areas farthest from the Ark adapted a more productive reproductive system.
Marsupialism is just a minor adaptation.
Some marsupials have no pouch at all or just develop one when pregnant.
its no big deal.
Regardless of the pouch opening it was a quick reaction to make a covered area for the fetus to suckle. The folds in the skin quickly being used and then DNA remembered. Just like the way squirrels etc developed their flaps to glide from trees to trees.

It is unlikely or impossible for the original marsupial from whence came all sorts of marsupials to switch pouches back to front as needed from selection on mutation.
Time does not explain anything.
its best to see marsupials as exactly as what they appear to be. just modified placental creatures from the first migrations in a post flood world.


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