Did viruses precede other life?

this is a good hypothesis, although i can't say that i agree with their conclusions. structural similarity without homology is prevelent in biology. one example is the transmembrane portion of cell surface proteins. they are all very similar although not homologous. this is because there is only one way to make them, i.e. helical with hydrophobic amino acids sticking out, and hydrophilic ones sticking in and there are only a small subset of amino acids that are hydrophilic or hydrophobic, so these will always be used, regardless of the homology.

viruses did share a common ancestor, but there is no way to time this ancestry based on these non-homologous proteins.

personally, i think that the invalid iconography of the perception of evolution, from simple to more complex, is biasing the estimation of the origin of viruses. I would not be surprised if one day we find that viruses evolved from a more complex life form, like a bacteria to its more simple form. there are many examples of this type of evolution, from complex to more simple, for example the pre-cursors to chloroplasts and mitochondria were more complex, and the precursers to some mammalian gut parasites. probably many others.
 
I don’t see how viruses could have existed before cellular life. Viruses need the machinery and cytoplasm environment of a cell to replicate. If the ancestor of viruses did exist at the dawn of life and could replicate outside of the cell then it was not a virus, it would need a new classification. Also just because proteins have homologies structures does not mean they are related: thats like saying bats were the descendents of Terrasaurs just because they both had a skin membraned wings. Many viruses show homology to virions and plasmids and show signs of having evolved from their host rather then independently.
 
I was just reading an article the other day about rna lifeforms that might have preceded dna. This sounds like the most likely scenario to me. I think it was some dude at Harvard doing the research. He's been experimenting with creating simple rna structures that can replicate themselves with a minimum of errors. They use natural fats to create a membrane of sorts. They've also found that clay helps the vacuoles to form with bits of rna trapped inside. I think borax is involved too. It sounds like he's still got a long way to go, but it sounds promising.

I agree with WellCookedFetus about the probable origins of virii. Coming out of the cell rather than before. Is there a single virus known that doesn't need a foreign cell to replicate? If virii were first, surely some of these original virii would have survived that didn't need another cell.
 
WellCookedFetus said:
I don’t see how viruses could have existed before cellular life. Viruses need the machinery and cytoplasm environment of a cell to replicate. If the ancestor of viruses did exist at the dawn of life and could replicate outside of the cell then it was not a virus, it would need a new classification. Also just because proteins have homologies structures does not mean they are related: thats like saying bats were the descendents of Terrasaurs just because they both had a skin membraned wings. Many viruses show homology to virions and plasmids and show signs of having evolved from their host rather then independently.
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I barely can remember the article that I have posted, but I guess that it's not suggesting that virus really precedes all the other life, but just precedes major splits into actual kingdooms. Virus may descend from something like archaea or have a common ancestor with them, I guess.

About the inference of relatedness based on structure rather than in genetics, I guess that it's valid in some cases. I've read somewhere, that hemoglobin and chlorophyl are suposed to descend from a common chemical ancestor due to its similarity to each other...
 
Danniel said:
I barely can remember the article that I have posted, but I guess that it's not suggesting that virus really precedes all the other life,
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I think that was the point;

"Viruses share a common ancestor that existed over 3 billion years ago and may even have preceded cellular forms of life, according to a report in the May 3 PNAS by George Rice and colleagues at Montana State University."

My concern is that they're trying to fix a clock on potentially analogous rather than homologous genes that're based merely on structural similarity that would be under strong purifying selection, which is probably not valid.

I'll try to read the original PNAS paper and get back to you.
 
WellCookedFetus said:
Also just because proteins have homologies structures does not mean they are related:
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actually, and this is besides your point which is a good one, but, by definition homology means identity by descent, i.e. related. I think you mean analogy.
 
Danniel,

heme groups could have evolved independently of each other, only when you have domains on the proteins that are homologies by dna sequence should your really suspect common ancestry.
 
WellCookedFetus said:
Danniel,

heme groups could have evolved independently of each other, only when you have domains on the proteins that are homologies by dna sequence should your really suspect common ancestry.
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But isn't that sort of inference like cladistics for microbiology? Cladistics don't need the dna sequence to be traced, it's just inferred by similarity in structures (or similarities anything else avaliable). But it can be a trap, of course...
 
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Danniel said:
But isn't that sort of inference like cladistics for microbiology? Cladistics don't need the dna sequence to be traced, it's just inferred by similarity in structures (or similarities anything else avaliable). But it can be a trap, of course...
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cladistics assumes homologous characters whatever they are (i.e. morphological, molecular etc.)
 
homologies does not need to imply common ancestry, only similarity.

Main Entry: ho·mol·o·gy
Pronunciation: hO-'mä-l&-jE, h&-
Function: noun
Inflected Form(s): plural -gies
1 : a similarity often attributable to common origin
2 a : likeness in structure between parts of different organisms due to evolutionary differentiation from the same or a corresponding part of a remote ancestor -- compare ANALOGY b : correspondence in structure between different parts of the same individual
3 : similarity of nucleotide or amino-acid sequence in nucleic acids, peptides, or proteins
4 : a branch of the theory of topology concerned with partitioning space into geometric components (as points, lines, and triangles) and with the study of the number and interrelationships of these components especially by the use of group theory -- called also homology theory; compare
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WellCookedFetus said:
homologies does not need to imply common ancestry, only similarity.
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they absolutely do mean common ancestry in the context of evolutionary biology. absolutely no question about it. wherever you found that definition (i don't see a link BTW) it appears your definition is taken out of the context of evolutionary biology or "by common descent" is implied in part 3 of the definition you provided. you would need to ask the author of the definition, however, you cannot argue what homology means in the context of evolutionary biology. it is crystal clear.

here's what homology means in the context in which we are using it in this thread;

"homology and analogy

Similarity due to Common Ancestry (homology) of trait (may inform us about control systems)
"Common ancestry is shared by two characters if in principle each can be shown to have evolved from the same character in a common ancestor." (Hailman p183)

Similarity due to Common functions (analogy) of trait. (generally attributed to parallel or convergent adaptation -- May inform us about ecological adaptiveness of trait)
An extreme example of analogy: The ripples on the skin of a fast moving porpoise and in the endothelial lining of a blood vessel -- both responses to comparable adaptive needs."

from http://notes.utk.edu/bio/greenberg.nsf/0/9e1f62a13ea9da7c8525684100754aff?OpenDocument

AND

"homology -- Similarity in characteristics resulting from shared ancestry.

homologous structures -- Structures in different species that are similar because of common ancestry.

analogy -- The similarity of structure between two species that are not closely related; attributable to convergent evolution.

-- from the Glossary, Biology, N. Campbell"

from

http://web.grinnell.edu/individuals/brownj/edu/136_lab1.html


AND

"homology In this essay, since we are not assuming the truth of common descent, "homology" simply refers to similar structures, regardless of function. In evolutionary biology, structures are homologous only if they were derived from the same structure in a common ancestor. "Homology" in evolutionary practice is thus a hypothesis which can be tested, and which can garner various levels of evidential support (primarily taking into account all available phylogenetic evidence). Importantly, there exist multiple levels of homology in biology. What is evolutionarily homologous at one level may not be so at a lower level or at a higher level (Dickinson 1995). The causal chain in biology is discontinuous, including genes, genetic networks and pathways, cells, cell types, developmental pathways, organs, and organisms. Though each level is dependent upon the preceding level, functions at one level can be redundant (due to the stochastic and opportunistic nature of evolution), and thus functions are occasionally free to shift, resulting in uncoupling between levels of homology. This fact has caused some confusion in practice for the precise application and delineation of the homology concept. For example, the genes which control the development of eyes are homologous between vertebrates and invertebrates, yet the organs (the eyes themselves) are not (i.e. they evolved convergently into very different structures having somewhat similar functions). Also see parahomology, analogy, and convergence."

from http://www.talkorigins.org/faqs/comdesc/glossary.html

i could probably provide another thousand references.
 
I'm tired of you always contradicting me, what’s your problem? Do you even realize how off topic this is? (I bet your going to say something like "no it not")

I’m sorry but I disagree with you, I placed an example of it being used or alowed to be used in contacts with similarity only implied, I placed a exception to your rule, thus it can be used in stating similarity only. That’s the way I was taught to use it, live with it. We are talking about homology between proteins and in biochemistry we state homology as to mean similar to by sequence. Proteins have homologies domains does not necessarily mean they are related.
 
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WellCookedFetus said:
I'm tired of you always contradicting me, what’s your problem? Do you even realize how off topic this is? (I bet your going to say something like "no it not")

I’m sorry but I disagree with you, I placed an example of it being used or alowed to be used in contacts with similarity only implied, I placed a exception to your rule, thus it can be used in stating similarity only. That’s the way I was taught to use it, live with it. We are talking about homology between proteins and in biochemistry we state homology as to mean similar to by sequence. Proteins have homologies domains does not necessarily mean they are related.
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It's too bad you're tired, but when you're wrong, you ought to be big enough to admit it, instead you spend three days to find a mis-definition, post it, to mislead the readers who are actually trying to learn something here
 
paulsamuel,

What gives you the idea I'm misleading the reader?, I'm using the word rather correctly for my field. It’s you that has to have a problem and argue over something like this. Why don’t you be the mature one and act your age and not pick on the smallest little differences, and stick to the topic. It's hard to believe your a competent adult with a meaningful life if you spend your time arguing like this on a internet forum, again whats your problem???
 
WellCookedFetus said:
paulsamuel,

What gives you the idea I'm misleading the reader?, I'm using the word rather correctly for my field. It’s you that has to have a problem and argue over something like this. Why don’t you be the mature one and act your age and not pick on the smallest little differences, and stick to the topic. It's hard to believe your a competent adult with a meaningful life if you spend your time arguing like this on a internet forum, again whats your problem???
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When you misuse the word 'homology,' and i very nicely point out to you that you've misused it (and i added a compliment when i corrected you), you were not big enough to just learn the lesson, thank me, and move on. You have to insist that you weren't wrong and come up with a lame definition with no link. This is misleading, because you know better. You know that I'm right, and you know the difference between analogy and homology, but you won't admit your mistake, thereby misleading the reader.

You may think it's trivial, but the terms mean the opposite thing and all communication breaks down when you say homology when you mean analogy and other people trying to learn something get all frustrated and give up and you've put them off science, all because you can't admit your mistake.

The rest of your post is bullshit, just personal attacks so I won't comment on those.
 
I have to back up Paulsamuel here.

If you talk about 'homologous structures of a protein' you are clearly talking about a common origin.

Maybe these definitions are a bit more variable outside biology but for a biological topic the definitions are very clear cut.
 
I did not misuse the word homology, It still within the limits of it definition, period. And you two always go against me all you like, but that not going to change the field of biochemistry or the terminology used in it. I don't see any of that as personal attack I really want to know why you always do this??? I have many theories on it, but I would love you to provide you’re on explanation.
 
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