Freethought & Rationalism Archive

greenbear · 10-02-2003, 01:08 AM

Quote:

Originally posted by Badfish
So anyway science could still be wrong here, not too long ago science was absolutely positive the sun revolved around the earth, it's the nature of science, its discoveries could and DO change over time.

No, that would be religion which included geo-centrism as part of it's dogma.

lpetrich · 10-02-2003, 01:08 AM

Charles Darwin:
Pseudogenes are an interesting evidence, but you are mistaken if you think creationism has no explanation.

Sure. It was created to look like the result of evolution [sarcasm].

And there is, of course, the pre-Darwinian explanation I had mentioned earlier in this thread, that it's some sort of taste for completeness -- our genomes would not be complete without broken urate-oxidase and GLO genes.

Another explanation would be that there is a yet to be discovered function.

IMO, it takes a LOT of faith to believe that.

This may seem unlikely, but remember the track record of all those "useless" functions.

Let's see your vestigial-feature functionality scorecard. A list of features, with when proposed to be vestigial, and when shown to be functional.

lpetrich · 10-02-2003, 01:33 AM

Charles Darwin:
Yes, I did provide arguments. If there was some long-since dormant "tooth" genes they would have incurred probably too many mutations to be useful by this time. Instead, the teeth only grow when the mouse tissue is applied. ...

This suggests that many vestigial features are maintained as side effects of other processes. Thus, tailless land vertebrates grow embryonic tails because their growth is a side effect of the spinal-cord layout mechanism. And embryonic gill arches, gill pouches, and aortic arches are maintained because suppressing all but the "necessary" ones would break the mechanisms for making them.

A clue comes from the genetics of Manx-cat taillesness. Cats have a gene involved in producing tails that can either be normal (m) or Manx (M). Since cats are diploid, they have two copies of that gene:

mm -- "normal" tailed cat
Mm -- Manx cat (stubby or absent tail)
MM -- dies as an embryo

So the M allele must break some mechanism that the m allele fits into. The combination Mm would be partial breakage, enough to allow the cat to survive, though with tail growth suppressed. The combination MM would be complete breakage, complete with killing the embryo.

However, taillessness does evolve, and it likely evolves if there is some penalty to having a tail, like it getting entangled in branches. This may force selection for the presence of a "Manx" gene in the population -- and subsequent selection of mutations that make the "Manx" gene less troublesome.

Badfish · 10-02-2003, 01:34 AM

Quote:

Originally posted by greenbear
Yes, science does have ideas on how life began. Unlike Creationists, science demands credible evidence before accepting theories.

What evidence? There is no demonstratable evidence from either side.

Badfish · 10-02-2003, 01:37 AM

Quote:

Originally posted by greenbear
No, that would be religion which included geo-centrism as part of it's dogma.

Yeah, but science at the time believed it and even made models explaining how it worked.

Badfish · 10-02-2003, 01:39 AM

Quote:

Originally posted by greenbear
It doesn't nullify Zark the space lizard either.

He sounds cool, whats his angle?

Badfish · 10-02-2003, 01:42 AM

Quote:

Originally posted by greenbear
What do you consider the most likely cause?

Well considering that all life as we can observe it contains the same basic DNA (all organisms contain the famous double helix), and the millions of unique species in spite of sharing this quality, it sure seems like design with a signature.

Also, something from nothing, could suggest a designer.

Wounded King · 10-02-2003, 01:45 AM

Quote:

Originally posted by Charles Darwin
Instead, the teeth only grow when the mouse tissue is applied. The mouse tissue is necessary for anything to happen.

Not for anything to happen. This paper shows that chick skin mesenchyme, which expresses FGFs and BMPs or beads soaked in FGF4 and/or BMP4 were capable of inducing the development of rudimentary structures, more developed than the normally present lamina like rudiments, in chick mandibles. These structures also show Sonic hedgehog expression in a pattern similar to that seen in the developing mouse tooth germ.

Quote:

Chen Y, Zhang Y, Jiang TX, Barlow AJ, St. Amand TR, Hu Y, Heaney S, Francis-West P, Chuong CM, Maas R.
Conservation of early odontogenic signaling pathways in Aves.
Proc Natl Acad Sci U S A. 2000 Aug 29; 97(18): 10044-10049.

Teeth have been missing from birds (Aves) for at least 60 million years. However, in the chick oral cavity a rudiment forms that resembles the lamina stage of the mammalian molar tooth germ. We have addressed the molecular basis for this secondary loss of tooth formation in Aves by analyzing in chick embryos the status of molecular pathways known to regulate mouse tooth development. Similar to the mouse dental lamina, expression of Fgf8, Pitx2, Barx1, and Pax9 defines a potential chick odontogenic region. However, the expression of three molecules involved in tooth initiation, Bmp4, Msx1, and Msx2, are absent from the presumptive chick dental lamina. In chick mandibles, exogenous bone morphogenetic protein (BMP) induces Msx expression and together with fibroblast growth factor promotes the development of Sonic hedgehog expressing epithelial structures. Distinct epithelial appendages also were induced when chick mandibular epithelium was recombined with a tissue source of BMPs and fibroblast growth factors, chick skin mesenchyme. These results show that, although latent, the early signaling pathways involved in odontogenesis remain inducible in Aves and suggest that loss of odontogenic Bmp4 expression may be responsible for the early arrest of tooth development in living birds.

Jack the Bodiless · 10-02-2003, 01:49 AM

Don't some birds grow teeth anyhow?

The expression "as rare as hen's teeth" is a lot older than modern genetic engineering...

NottyImp · 10-02-2003, 02:16 AM

Quote:

Why wouldn't we ask about your judgement? Are you satisfied that science hasn't the slightest idea how life Began?

But evolutionary theory isn't contingent on abiogenesis. I'm not personally familiar with the field, but I'm pretty sure that there is plenty of research into this going on right now.

Why do you insist that science must know the answers now? One hundred years ago we had no clear idea how the sun generated its energy, but now we do. Genetic research is still a relatively new field, and there is a huge amount of research still to be done. Thus the "God of the Gaps" will continue to recede.

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10-02-2003, 01:08 AM	#582
lpetrich Contributor Join Date: Jul 2000 Location: Lebanon, OR, USA Posts: 16,829	Charles Darwin: Pseudogenes are an interesting evidence, but you are mistaken if you think creationism has no explanation. Sure. It was created to look like the result of evolution [sarcasm]. And there is, of course, the pre-Darwinian explanation I had mentioned earlier in this thread, that it's some sort of taste for completeness -- our genomes would not be complete without broken urate-oxidase and GLO genes. Another explanation would be that there is a yet to be discovered function. IMO, it takes a LOT of faith to believe that. This may seem unlikely, but remember the track record of all those "useless" functions. Let's see your vestigial-feature functionality scorecard. A list of features, with when proposed to be vestigial, and when shown to be functional.

10-02-2003, 01:33 AM	#583
lpetrich Contributor Join Date: Jul 2000 Location: Lebanon, OR, USA Posts: 16,829	Charles Darwin: Yes, I did provide arguments. If there was some long-since dormant "tooth" genes they would have incurred probably too many mutations to be useful by this time. Instead, the teeth only grow when the mouse tissue is applied. ... This suggests that many vestigial features are maintained as side effects of other processes. Thus, tailless land vertebrates grow embryonic tails because their growth is a side effect of the spinal-cord layout mechanism. And embryonic gill arches, gill pouches, and aortic arches are maintained because suppressing all but the "necessary" ones would break the mechanisms for making them. A clue comes from the genetics of Manx-cat taillesness. Cats have a gene involved in producing tails that can either be normal (m) or Manx (M). Since cats are diploid, they have two copies of that gene: mm -- "normal" tailed cat Mm -- Manx cat (stubby or absent tail) MM -- dies as an embryo So the M allele must break some mechanism that the m allele fits into. The combination Mm would be partial breakage, enough to allow the cat to survive, though with tail growth suppressed. The combination MM would be complete breakage, complete with killing the embryo. However, taillessness does evolve, and it likely evolves if there is some penalty to having a tail, like it getting entangled in branches. This may force selection for the presence of a "Manx" gene in the population -- and subsequent selection of mutations that make the "Manx" gene less troublesome.

10-02-2003, 01:49 AM	#589
Jack the Bodiless Veteran Member Join Date: Feb 2001 Location: UK Posts: 5,815	Don't some birds grow teeth anyhow? The expression "as rare as hen's teeth" is a lot older than modern genetic engineering...

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