Warthaug
QUOTE=Warthaug;3658811]They went extinct, or evolved into something else. Skin doesn't fossilize well, so we don't know when that adaptation came about - although it would have to be old enough to be found in all major branches of sharks. The fundamental shape of sharks is much older than sharks themselves - the basic body shape of sharks can be found in some of the first fish - Agnathans - which evolved 50-100 million years before sharks did.
It's not that complex - there is a group of marsupials (which includes wombats and koalas) who have backwards-facing pouches. In the case of wombats this is a good thing, as dirt doesn't get in. In the case of Koala's it makes little sense; it actually increases the risk of the young falling from a tree.
The reason for the pouch orientation is simple - that's what their ancestors had, and when they diverged they kept that adaptation; even though in the case of the koala it is a mild disadvantage.
As for where the first "backwards" pouch came from, no one knows. Pouches don't fossilize well, so there isn't any fossil record. Off the top of my head, I can think of three biologically plausable explanations as to how this occured:
1) Wombats/Koalas are "backwards", and evolved from a "forwards" predecessor. I don't know much about the developmental biology of marsupials, but assuming they're like the rest of the mammals, and that their pouch forms via the same invagination process that forms all the other organs, moving the opening would require nothing more than a single mutation in a morphogen's receptor.
2) "Backwards" pouches have been the first pouches, and its the rest of the marsupials which have it backwards. As above, this only requires a single mutation in a morphogen receptor.
I would add at this point that #'s 1 & 2 are the least likely, based on how mammals evolve, as morphogens tend to be used in many locations, so a mutation in a morphogens receptor would probably royally screw up the animal. That said, marsupials may have a dedicated morphogen for their pouch, at which point the above possibilities actually become the most likely.
Any experts on the developmental biology of marsupials out there?
3) Most likely, the orientation of the pouches are a result of divergent evolution from the pre-pouch form. For example, modern pouches may have started off as a flap of skin, or small hollow. In this case evolution, occurring of many generations could have deepend and altered the predecessor structure to the two different forms we see today.
Nice explanation but in reality doesn't that assume there was a wombat with a pouch upright? ...and if they were burrowing mammals a fossil or two would be highly likely
It's been a while since I went to church, but if memory serves me, satan is the father of lies... Where's the lie? Ultimately if God created Adam and Eve as sexually mature adults, why is it a deception to say the Earth was also mature.
Any how, what about those of us who:
a) don't give a damn about god, and are simply exploring the universe in which we live (that would be me, btw), or
b) are devoutly Christian, and use science as a way of exploring gods universe?
So you run upon a fossil. You either give God the glory or you don't
Of course, you've been ignoring the fact that most Christian denominations accept evolution, and that many scientists are also Christians. Of course, I'm sure you'll rationalize that through the usual they are not "real christians" as they don't follow the very narrow interpretations of my faith...
First, I would never judge another's salvation. Its not my place. Secondly, there are "essentials" of the Christian faith and oddly enough none of them have to do with one's interpretation of Genesis. Someone asked for another theory (for short I assume they mean't hypothesis) and I gave them one. I think your statement about evolution being accepted by most denominations is incorrect. Especially not as it has been defined on here
But what keeps him from using evolution? Or, for that matter, dumbing things down for sheppard's who don't have the educational background (or even language) to understand and intelligently discuss complex things like quarks, atoms, space-time continuum, abiogenesis and evolution...
If the Bible doesn't stand as God's inerrant word then where does that leave Christianity? I guess its a lot like the Brontosaurus issue with me. If something stands as incorrect, then it brings into question the entire field/product/book. So if Genesis didn't occur as described, then was it metaphorical or was it inaccurate? Now, before someone points me to the billion or so percieved errors in scripture, suffice it to say I've read most of them. Furthermore, we could dedicate another 600 or so posts to the subject. Something most of us don't have time for. So, while I don't pretend to know the exact answer...ie God behind evolution, I don't dismiss this view either.
Bryan[/QUOTE]
