Jump to content
Sign in to follow this  
Carl Sagan

A Vigorous Exposition of Evolution and its Appositeness for Xenosociobiology

Recommended Posts

Well, I guess if you put it that way, then I don't know if the chemistry of life on Earth is the only possible chemistry. But, to back my point up, DNA is the only known molecule that can self-replicate, and that is needed for life to actually exist. Also, even the life that live in extreme conditions are carbon based.

Share this post


Link to post
Share on other sites
Well, I guess if you put it that way, then I don't know if the chemistry of life on Earth is the only possible chemistry. But, to back my point up, DNA is the only known molecule that can self-replicate, and that is needed for life to actually exist. Also, even the life that live in extreme conditions are carbon based.

 

Right, I brought up the point about the carbon based usage even in extreme environments. It is apparent though going through evolution from say prokaryote to eukaryote the simple differences such as having a cell nucleus. Which can prescribe easily the thought that life may have at one point not had any of the common structures it has today, simply because it did not automatically from the start have these structures, such as limbs or kidneys for instance, or a cell nucleus.

 

IF carbon is required by life, or DNA for that matter, I cant say either way with any real confidence because the reality we have on earth of course is organismal life or life in general that shares in its chemistry, such as carbon use for example, but it does not again state that such is the only way or natural law of such because we cant compare it with anything, unlike gravity which we know exists in nature besides earth. The one thing though is the variation is chemistry possible in life already can easily make a point about what’s available for use chemically speaking.

Share this post


Link to post
Share on other sites
Well, I guess if you put it that way, then I don't know if the chemistry of life on Earth is the only possible chemistry. But, to back my point up, DNA is the only known molecule that can self-replicate, and that is needed for life to actually exist. Also, even the life that live in extreme conditions are carbon based.

 

1. DNA does not "self-replicate". It needs an astonishing number of proteins for duplication. What DNA does is preserve the sequence of bases.

 

2. RNA can self-replicate! And, since there are ribozymes (RNA that acts like enzymes), there are actually RNA strands that can self-replicate. :)

 

3. There are also simpler nucleic acids, one of which is based on the sugar threose rather than ribose: 18. L Orgel, A simpler nucleic acid. Science 290: 1306-1307, Nov 17, 2000. 222/sciencemag.org/cgi/content/full/290/5495/1306

 

4. For "life" to exist, all you need are proteins. What you need DNA/RNA for is directed protein synthesis.

Share this post


Link to post
Share on other sites
I don’t know the exact time or concentrations of certain chemistries geologically speaking on earth, and I think knowing such would be paramount overall.

 

No, you don't need that. There are lots of different ways to make amino acids and sugars, and lots of different ways to get amino acids to make first proteins and then protocells. The conditions are so flexible that it is virtually certain that somewhere on a planet one of the conditions would be present.

 

Now just give me a second, I have not tried to see the validity of such, but I sometimes by accident in thought associate gibbs free energy with geological differentiation, I think during the "primordial soup" we have a lot of missing issues that attack directly the topic here, environments that do not exist today moreover.

 

It's obvious you didn't try "to see the validity" of associating Gibbs free energy with geological differentiation. Because there is no association and a moment's thought would have shown that.

 

Do you just throw out scientific terms at random? It appears that way, because you show no comprehension of the terms you use.

 

For instance, why is the non metals sections so used?

 

Because the non-metals section can form polymers thru covalent bonds. Metals can't do that. The association of metal to metal is ionic, not covalent.

 

Does this define a base chemistry needed for life regardless of environment, a chemistry required by natural selection in regards to a particular environment, or does the chemistry of life have to equate to the more primordial chemistry of early life, such as the protocell.

 

Such muddled thinking! First, let's separate chemistry from natural selection. Natural selection will act once chemistry has made an entity that can reproduce. Until then, natural selection can't work because natural selection requires heredity -- which in turn requires reproduction.

 

Second, you need chemistry to get to the protocell. The protocell is not "chemistry of life" but rather the product of chemistry.

 

Third, you have to remember the key role that water plays in the chemistry of life -- biochemistry.

 

I think a big part of it is overcoming the perceptual boundary really from the physical to what is "life" really.

 

Not a problem. In order to be alive, an entity must exhibit ALL of the following criteria: metabolism, growth, response to stimuli, and reproduction.

 

The proton gradient in cells is also another point, in which does it only react to a certain sect of say ions for instance, a chemical recognition or such, I think this could even tie into why symmetry is so present in life and even used in mate selection. Supposedly asexual reproduction is less efficient the sexual reproduction, so it all has physical points to study.

 

:confused: WOW, you do throw stuff out at random. Since you are obviously a lost cause for careful thought, the rest of the post is for the other members of the thread.

 

Asexual reproduction is more efficient than sexual reproduction, but does not have as much variation among offspring. Recombination produces orders of magnitude more variation than mutation.

 

Symmetry -- such as bilateral symmetry -- is not due AT ALL to electrochemical gradients within cells. It has to do with embryological development in multicelled organisms and gradients of morphogenetic proteins produced by cells.

 

Electrochemical gradients within individual cells is a side effect of having proteins be the major component of cell membranes. Even modern cells have over 50% of their cell membranes as proteins, not lipids. You can make protocells out of only proteins and no lipids and they have cell membranes -- and electrochemical gradients. In fact, they have action potentials identical to nerve cells!

 

I am trying to get some good books on prokaryotes currently, because I am interested in symbiotic relationships, the appearance of an immune system and why DNA/RNA happen to exist, but RNA in prokaryotes with a genetic shift to eukaryotes at some point.

 

1. DNA/RNA exist because they can be faithfully replicated and serve as a template for directed protein synthesis. This is more efficient than proteins making other proteins in that each new protein will be identical -- coming from the same template.

 

2. Eukaryotes may have been first and prokaryotes are a simplification of them. This paper argues for a eukaryotes first approach:

9. AM Poole, DC Jeffares, D Penney, The path from the RNA world. J. Molecular Evolution 46: 1-17, 1998.

 

Do a PubMed search on Penney and you will find other papers by him arguing for a eukaryote first approach.

 

I would like to see as pollution changes the environment more and more, how this registers in metabolic pathways

 

There is one very famous way in which pollution has opened a new metabolic pathway: use of nylon as food.

1. Birth of a unique enzyme from an alternative reading frame of the pre-existed, internally repetitious coding sequence", Ohno, S, Proc. Natl Acad. Sci. USA 81:2421-2425, 1984. Frame shift mutation yielded random formation of new protein, was active enzyme nylon linear oligomer hydrolase (degrades nylon) http://www.nmsr.org/nylon.htm

Share this post


Link to post
Share on other sites
we have not synthesized life yet,

 

Yes, we have. http://www.theharbinger.org/articles/rel_sci/fox.html

 

1) Is the chemistry of life on earth the only possible chemistry for life?

2) Is the chemistry of life on earth the only possible chemistry for life in regards to the earths environment?

3)Is the chemistry of life on earth nothing more then the only possible evolutionary progression from the more primordial life, such as the "protocell".

 

1) depends on how you define "chemistry of life on earth". There are hundreds of amino acids, for instance, but life on earth only uses 20 or so of them. Could life on another planet use different amino acids in their proteins? Maybe to some extent, but remember that the simple chemical reactions to form amino acids are going to make some of them (the common ones among the 20 used in earth life) in a lot greater quantities than others.

 

2) again, depends on how you define "chemistry of life".

 

3) No. we can see this in variations on the various metabolic pathways among living organisms. There could easily be different metabolic pathways using different chemicals. For instance, we can see among earth living organisms different sources of energy: sulfides, sugars, etc.

 

I mean silicon might not be a favorable chemistry on earth, but that does not hold true for every possible environment in the universe I imagine. I mean all kinds of complex compounds exist in chemistry that do not use carbon.

 

But those "complex compounds" don't form polymers. Only carbon and silicon can form long chain polymers of binding C-C or Si-Si. Any hereditary chemical for complex cells is going to have to be a polymer -- to be long enough to have genes -- and that means either carbon or silicon based.

 

You also have to consider the role of water in biochemistry. Water isn't a passive solvent that just happens to be around. The chemical properties of water -- its polarity -- is an essential part of life.

 

Before you post any more incoherencies on this board, why don't you get a copy of Lehninger's Biochemistry and read it. Once you have a foundation on the chemistry of life as we find it on earth, THEN you might be able to have some coherent thoughts on the subject of life that is not carbon based, or protein based, or nucleic acid based.

 

To me there is no real evidence yet that can get close to answering any of the questions I have posed save for someone to be confident in a hypothesis.

 

Yes, there is evidence. You simply are either unaware of it or won't look for it.

 

BTW, it is easy to "be confident in a hypothesis" if you have tested the hypothesis against evidence. Hypotheses are NOT "wild guesses". There are many hypotheses that are so well-supported that they have the status of "fact". Just one hypothesis with the status of fact is: RNA/DNA is the hereditary material in living cells.

Share this post


Link to post
Share on other sites

Another to speculate on then is how gravity would affect the evolution of life. The planets that we find that may have life on them will not necessarily be the same size as Earth.

Share this post


Link to post
Share on other sites

A whale will be able to glide on a planet which has less gravity.

Share this post


Link to post
Share on other sites
Another to speculate on then is how gravity would affect the evolution of life. The planets that we find that may have life on them will not necessarily be the same size as Earth.

 

This gets back to basic physics and its influence on design by natural selection. Gravity is going to influence the possibilities of design. If you want to see such speculation, I suggest the science fiction of Poul Anderson; he was very good at creating different worlds and the evolution of plants and animals to inhabit them.

 

Much lower gravity is going to mean that flight is easier and that more massive creatures will be able to fly. Higher gravity is going to impose restrictions on the size of creatures relying on exoskeletons and require more massive bones (and muscles) for endoskeletal land dwellers. Also, creatures are more likely to be low to the ground so that falls will be less likely to result in broken bones.

 

It's fairly easy to speculate on generalities: simply look at the constraints and consequences of the physics. The particulars get messy because you then have to deal with the contingencies of evolution.

Share this post


Link to post
Share on other sites

"Zoological Physics" (Ahlborn) is a very good book about the limits imposed by the laws of physics.

Share this post


Link to post
Share on other sites
Interested in personal qualm or agreement behind acquired residuums.

 

Residua ... oh the demise of a classical education!

 

Rest in Peace Carl.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.