Freethought & Rationalism Archive

lpetrich · 04-07-2003, 04:56 PM

Nowhere357, you want to find out more about comparative anatomy and embryology, there is a lot of stuff on the Internet about these subjects. Now some clarifications:

It's only the first set of gill bars that develop into jaws; that is the origin of jaws in jawed vertebrates. And in amniotes (full-time land vertebrates and their aquatic descendants), the other gill bars and gill slits get either reused for other functions or resorbed.

Likewise, circulation starts out very fishlike, with aortic arches along the gill bars. In amniotes, the circulation gets reorganized as the embryo grows, with some parts of the dorsal aortas dropping out and some of the aortic arches also dropping out.

The heart, which is two-chambered in fish, becomes three-chambered in amphibians and turtles, lizards, and snakes, and four-chambered in mammals, crocodilians, and birds. And does so by becoming split into two sub-hearts.

There are, however, some differences; amniote embryos are stubbier than fish embryos. However, amniote embryos look remarkably similar; compare human and chicken embryos, both of which are very well-documented.

lpetrich · 04-07-2003, 05:00 PM

As to the origin of life, here is my favorite crackpot theory:

That the Earth was seeded by time travelers from our future who wanted to insure that they would eventually come into existence.

Albion · 04-07-2003, 11:04 PM

Quote:

I would guess he means that abiogenesis assumes the existence of evolutionary theory.

OK, I was wondering if he meant evolutionary theory or extraterrestrials. Either way, it doesn't, it just assumes that the laws of nature were in operation and the materials and conditions were favourable, but I was wondering if we had a panspermia advocate here or something.

Nowhere357 · 04-09-2003, 02:32 AM

Quote:

Originally posted by Albion
Abiogenesis assumes e.t.? Could you clarify?

Sorry. ToE?

The point I'm trying to explore is that the existence of life cannot be derived from our (current) understanding of reality. The existence of life (or the tendancey of life to arise from matter) is assumed, as if it were a fundamental property, and yet it seems we don't look at it that way. I'm trying to find out why.

Nowhere357 · 04-09-2003, 02:37 AM

Quote:

Originally posted by Wounded King
In what way do Newtons laws of motion "assume life"?

In addition to the answer I've given already, there is also this concept: all knowledge requires a knower! The existence of "minds" and therefore life, is directly implied.

Nowhere357 · 04-09-2003, 02:52 AM

Quote:

Originally posted by Darwin's Beagle
Here is what I think you are saying:

(1) You have no problem with evolutionary theory. Once life gets started everything else could have arisen by descent with modification. Natural selection and other neodarwinian mechanisms are sufficiently powerful to generate present-day diversity from a universal common ancestor.

Yes.

Quote:

(2) The origin of life, however, is another question. The laws of nature are such that without some type of directing intelligence life would never have begun in the first place.

Yes it's another question; No, I do not suspect a directing intelligence.

Intelligence, mind, self, and all such words currently have meaning to me only in the context of biological life, specifically life with an advanced central nervous system.

The point I'm trying to explore is that the existence of life cannot be derived from our (current) understanding of reality. The existence of life (or the tendancy of life to arise from matter) is assumed, as if it were a fundamental property, and yet it seems we don't look at it that way. I'm trying to find out why.

Nowhere357 · 04-09-2003, 03:08 AM

Quote:

Originally posted by Albion
OK, I was wondering if he meant evolutionary theory or extraterrestrials. Either way, it doesn't, it just assumes that the laws of nature were in operation and the materials and conditions were favourable, but I was wondering if we had a panspermia advocate here or something.

ToE.

I had said: "Abiogenesis assumes the existence of evolutionary theory." I think it does. Can the laws of ToE be derived from the laws of abiogenisis? More basic - can the existence of life be derived from abiogenesis? If so, then can the laws of abiogenesis be derived from the laws of physics? No, IMO.

I've never been called a panspermia advocate before! The only thing I really advocate is to make the fewest presumptions possible.

The point I'm trying to explore is that the existence of life cannot be derived from our (current) understanding of reality. The existence of life (or the tendancy of life to arise from matter) is assumed, as if it were a fundamental property, and yet it seems we don't look at it that way. I'm trying to find out why.

Wounded King · 04-09-2003, 03:56 AM

The fact that we do not know the precise mechanism of abiognesis, as yet, does not mean we cannot know it.

Nowhere357 · 04-09-2003, 04:16 AM

Quote:

Originally posted by Wounded King
The fact that we do not know the precise mechanism of abiognesis, as yet, does not mean we cannot know it.

Of course, WK.

First, I find the appeal of "omnipotent" science to be nearly as unsavory as the notion of god. As a matter of fact, I am directly aware of a part of the natural universe, which is not accessable to physical science. Literally.

Second, consider gravity. Assume for analogy sake, that instead of the tendancy of matter to form life, I am talking about the tendancy of matter to attract to itself. From my current POV, it seems like you are telling me that the tendancy of matter to attract to itself, is not a fundamental property: we don't know the precise mechanism, as yet, so there is no reason to assume a law of gravity.

Clearly, we formulated the law of gravity, without knowing the precise mechanism. Why, in your opinion, do we not do the same for the phenomenae of life?

Wounded King · 04-09-2003, 05:25 AM

In the case of gravity there are numerous instances where direct measurements can be made however. As far as we know there has been only one abiogenesis event, although this may not be the case even on earth, that has occurred, the one which gave rise to life on earth.

How do you propose we draw universal laws from one instance of something.

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04-07-2003, 04:56 PM	#21
lpetrich Contributor Join Date: Jul 2000 Location: Lebanon, OR, USA Posts: 16,829	Nowhere357, you want to find out more about comparative anatomy and embryology, there is a lot of stuff on the Internet about these subjects. Now some clarifications: It's only the first set of gill bars that develop into jaws; that is the origin of jaws in jawed vertebrates. And in amniotes (full-time land vertebrates and their aquatic descendants), the other gill bars and gill slits get either reused for other functions or resorbed. Likewise, circulation starts out very fishlike, with aortic arches along the gill bars. In amniotes, the circulation gets reorganized as the embryo grows, with some parts of the dorsal aortas dropping out and some of the aortic arches also dropping out. The heart, which is two-chambered in fish, becomes three-chambered in amphibians and turtles, lizards, and snakes, and four-chambered in mammals, crocodilians, and birds. And does so by becoming split into two sub-hearts. There are, however, some differences; amniote embryos are stubbier than fish embryos. However, amniote embryos look remarkably similar; compare human and chicken embryos, both of which are very well-documented.

04-07-2003, 05:00 PM	#22
lpetrich Contributor Join Date: Jul 2000 Location: Lebanon, OR, USA Posts: 16,829	As to the origin of life, here is my favorite crackpot theory: That the Earth was seeded by time travelers from our future who wanted to insure that they would eventually come into existence.

04-09-2003, 03:56 AM	#28
Wounded King Veteran Member Join Date: Mar 2003 Location: Edinburgh Posts: 1,211	The fact that we do not know the precise mechanism of abiognesis, as yet, does not mean we cannot know it.

04-09-2003, 05:25 AM	#30
Wounded King Veteran Member Join Date: Mar 2003 Location: Edinburgh Posts: 1,211	In the case of gravity there are numerous instances where direct measurements can be made however. As far as we know there has been only one abiogenesis event, although this may not be the case even on earth, that has occurred, the one which gave rise to life on earth. How do you propose we draw universal laws from one instance of something.

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