Extraplanetary Dimorphism?

[KerikBalm]

Perhaps a lifeform could assemble a full genetic profile by collecting a small amount of DNA from a series of "nodes" in it's environment and assembling them. These nodes would be a sort of egg filled with one particular gene that a lifeform could come and access for reproduction. Every organism that contained a certain gene would work to nourish that "node" during their life. Organism would mostly visit the nodes they had nourished during their life for reproduction but not necessarily all of them. Nodes could contain small amounts of variation, but this variation would be limited because of the small size of the genetics within them. New nodes could split-off from old nodes when enough diversity occurs, and I'm assuming mutation occurs at stable levels within the nodes, and during the creation of new nodes.

... I don't even know where to begin... what? ... that just makes no sense

How would such a system even get started? Are you supposing "intelligent design" of aliens rather than evolution?

I disagree. At least explain why you make that assertion, and yes, I will then produce a list of possible caveats that might satisfy whatever your concerns are.

FWIW, I'm don't even really know what your talking about with this cloning and mutation stuff. All I can say for now is Muller's Ratchet, and that you don't get to invent new meanings for words. (regarding an earlier comment about your "vision of cloning" and calling another "narrow").

You forget that both plants and animals are the descendents of the same great grandmother organism.

No, I don't

They share dna,

but they didnt share the same reproduction system. We all come from the last common ancestor... but we all do ... in different ways or not at all. The reasons for that are independent of the structure of DNA.

even though they develop new information, they can only derive that new information from variations of the old information they possess.

Please don't use this vague, undefined term "information", you sound like an ID tool.

Also, remember that all these creatures are responding to the same planetary environment, which is the driving factor of this convergence.

No, they are all responding to different parts of the environment. A tropical plant an an extremophile are in very different environments. And its not the environment that is the driving factor, it is innate feedback loops in any mutating genetic system.

The idea of aliens presupposes a likely lack of cellular structure, DNA, and maybe even biology as a whole.

No, it doesn't

I just dispute that cellular life that utilizes DNA would hardly even be worth considering an alien, more like just another "kingdom" in the biological classification system.

So if there was a completel independent genesis. On a rockey world... considering the laws of physics are the same in the universe, and pre-biotic chemistry can and does produce lipids, amino acids, and nucleotides (after all, you can find those even on comets, and in nebula based on the spectra).... if that life happened to evolve to contain DNA enclosed in lipids, you wouldn't call it alien....

Even if its genetic code was completely different, with no sequence homology to Earth life... but you'd say not alien....

Riiiiiigggggghhhhhtttttt.............

[Malokin]

... I don't even know where to begin... what? ... that just makes no sense

How would such a system even get started? Are you supposing "intelligent design" of aliens rather than evolution?

The nodes would be like our viruses, only larger and in the way that they contain snippets of dna that interact to form a larger organism in much the same way our viruses replace the dna of cells. This type of cycle could start with the nodes as the originating form of life with the other set of organisms as a mutation of the nodes with the ability to co-opt genetic data that was not from their parent node. From a single great grandfather node an entire kingdom of organism could arise that rely on nodes for reproduction rather than sexual reproduction as a way of facilitating evolution.

FWIW, I'm don't even really know what your talking about with this cloning and mutation stuff. All I can say for now is Muller's Ratchet, and that you don't get to invent new meanings for words. (regarding an earlier comment about your "vision of cloning" and calling another "narrow").

I believe I said the vision of cloning was narrow because you make automatic assumptions that mutations happen at incredibly high rates rather than the exact same rate of mutation we see on earth. It's a good idea to introduce problems to these ideas to see if they are stable, but it isn't helpful if the problem is easily solved. If you look at human cloning and say human cloning won't therefor this technique won;t work, you are ignoring that we aren't talking about human cloning, we're talking about a style of reproduction similar to cloning, or similar to the way cells reproduce within multicellular organism.

I've read what you've posted about Muller's Ratchet and even with that in mind I still assert that biological dimorphism is hardly the be all end all of all evolution. Other techniques could work as just well, or even better than sexual reproduction as long as they address the same challenges that sexual reproduction addresses with equal or better effectiveness.

No, I don't

I'm not saying that you don;t know this fact, I'm saying that when you try to say that sexual reproduction or even the many manifestations of eyes in our world are independent developments, you are incorrect, because those developments were mutations of the same starting dna. Thats really an odd way of using the term independent. It only stand to reason you end up with similiar convergent mutations when you start with the same beginning dna.

but they didnt share the same reproduction system. We all come from the last common ancestor... but we all do ... in different ways or not at all. The reasons for that are independent of the structure of DNA.

The ancestor organism we come from had a single reproductive mechanism, all other reproductive mechanisms are mutations of that system, and because of this convergence is not just possible but actually highly likely. If I give 1000 teams of builders the same building supplies, they can only create so much variation in their creations, EVEN IF they modify the parts we've given them. That's what is great about the thought experiment we are conducting now, we don't have to box ourselves into the already observed by assuming all the same starting parts (cells, DNA, etc), the same conditions on planet X, or even the presence of what we call biology.

Please don't use this vague, undefined term "information", you sound like an ID tool.

I apologize, I thought it was clear I was talking about genetic data, I just didn't want to use the term genetic for a creature with no DNA and no genes. The word genetic implies so many things I wish to leave out. Hereditary information or possibly reproductive information may have been a better term although they also carry implications that do not properly illustrate the endless possibilities of alien life.

No, they are all responding to different parts of the environment. A tropical plant an an extremophile are in very different environments. And its not the environment that is the driving factor, it is innate feedback loops in any mutating genetic system.

Very true, but there are commonalities between even the extreme environments you describe that we do not have to assume exist on planet X. Again I will use the example of cells. Cells are a great idea for the rigors of life on earth, but to an organism who lives on a planet with no wind, no tides, very little variance of terrain, constant and steady light, etc. a cellular covering would not necessarily be a requirement. Organelles on a string might suffice for these worm-like microscopic lifeforms.

You could even have a system of biological evolution with no death. A sort of fossil record of living organism birthed on top of, or below the parent living organism. Suitability/Survivability would not be defined by staying alive thru generation, but rather being able to find enough resources to reproduce. Grandpa and dad never die, but if junior cant get enough food to reproduce that evolutionary branch ends while his cousins who do find food continue on in life. This system still contains evolution and natural selection, even though every organism in the system is eternally living.

No, it doesn't

Yes, it does. Sure is easy to make baseless assumptions.

So if there was a completel independent genesis. On a rockey world... considering the laws of physics are the same in the universe, and pre-biotic chemistry can and does produce lipids, amino acids, and nucleotides (after all, you can find those even on comets, and in nebula based on the spectra).... if that life happened to evolve to contain DNA enclosed in lipids, you wouldn't call it alien....

Ha, your assuming this life is based on lipids, amino acids, and nucleotides. This is the error that limits your vision of alien life. When supposing aliens, you need not resort to those building blocks. I personally presuppose that carbon runs the show based on the laws of physics, but I find it hard to justify making the assumption, as you do, that this alien life MUST use the exact building blocks you have listed. It's not necessary for life that those things be included.

Even if its genetic code was completely different, with no sequence homology to Earth life... but you'd say not alien....

Riiiiiigggggghhhhhtttttt.............

Life evolves on a completley different world thru a completely different abiogensis event with a completely different environment and yet the organism still evolves itself cells, dna, sexual reproduction, etc etc. I'm gonna have to borrow your Riiiiiiiiggggggggggghhhhhhhhhtttttttttt for this one.

Even if we did find life like that, imagine we actually do discover life so amazingly similar to us as that: At that point which is more likely, that our exact biology propped itself up with the exact same characteristics thru a completely alien abiogenesis event, OR can we reasonable assume that these newly discovered organism are our panspermian cousins based on their physiology? I would assume the latter, which is why I say that such a similar creature is most likely not an alien at all, but rather just more of the same as we have already discovered on earth.

[comham]

It seems to me that most organisms that didn't reproduce at all would be, er, poorly adapted to their environment

[KerikBalm]

I believe I said the vision of cloning was narrow because you make automatic assumptions that mutations happen at incredibly high rates rather than the exact same rate of mutation we see on earth. It's a good idea to introduce problems to these ideas to see if they are stable, but it isn't helpful if the problem is easily solved. If you look at human cloning and say human cloning won't therefor this technique won;t work, you are ignoring that we aren't talking about human cloning, we're talking about a style of reproduction similar to cloning, or similar to the way cells reproduce within multicellular organism.

What are you talking about? Where did you get this idea of automatic assumptions of high mutation rates? What are you talking about with human cloning?

same starting dna. Thats really an odd way of using the term independent. It only stand to reason you end up with similiar convergent mutations when you start with the same beginning dna.

No it doesn't. Otherwise you would expect almost everything to be sexually reproducing. There was nothing innate in the DNA sequence of the LCA that favored ....

When you talk about the "same beginning DNA", you are ignoring that the a series of mutations in organisms that resulted in sexual reproduct, occured in organisms with orders of magnitude longer DNA sequences than the LCA, that were already highly diverged.

The ancestor organism we come from had a single reproductive mechanism, all other reproductive mechanisms are mutations of that system, and because of this convergence is not just possible but actually highly likely.

No, its not. We only see convergence when external factors dictate it. If there is an alien world with things swimming in a liquid ocean, they will adopt a hydrodynamic shape, as fish did, as icthyosaurs did, as marine mammals did. Its not because of starting DNA that they adopt hydrodynamic shapes.

Likewise, as organisms grow more complex, the allowable mutation rate grows smaller and smaller. This has nothing to do with DNA sequence, or even DNA, but is intrinsic to any system with discretely heritable units.

Yet organisms still need to adapt and change, so variation is needed. Thus you need recombination, where variations can be indicidually naturally selected, and combined...

And here we get to another limit of comple organisms - sometimes when you change "the blueprint" of something that is too complex, You have to build it again from scratch, not modify a previous iteration.

Also, its not clear which combination of the variations is even best, so you'll want to make multiple combinations, and test each one -> ie new organisms with that genetic combination - ie sexual reproduction.

I'll note that many organisms can switch between sexual and asexual reproduction. Some only switch to sexual reproduction when stressed... ie when their current genome isn't quite cutting it, they try out new variations.

This principle is inherent, it is not specific to DNA or sequences of life on Earth.

That is why it is likely to occur in complex aliens.

I apologize, I thought it was clear I was talking about genetic data, I just didn't want to use the term genetic for a creature with no DNA and no genes. The word genetic implies so many things I wish to leave out. Hereditary information or possibly reproductive information may have been a better term although they also carry implications that do not properly illustrate the endless possibilities of alien life.

"data" is equaly bad, just stick with "heritable unit".

Very true, but there are commonalities between even the extreme environments you describe that we do not have to assume exist on planet X. Again I will use the example of cells. Cells are a great idea for the rigors of life on earth, but to an organism who lives on a planet with no wind, no tides, very little variance of terrain, constant and steady light, etc. a cellular covering would not necessarily be a requirement. Organelles on a string might suffice for these worm-like microscopic lifeforms.

There are organisms on Earth that live in the conditions you specify, they did not give up their membrane. It is very hard to imagine life becoming very complex without discrete "cell like" units, and compartments to contain metabolic products. "organelles" on a string sounds very much like cells on a string. In fact, many of what we call "organelles" for our life are more properly regarded as endosymbiotic cells.

Yes, it does. Sure is easy to make baseless assumptions.[/quote[

Yes, it is easy to make such assumptions, you are the one doing it.

I quote: "The idea of aliens presupposes a likely lack ".....

"presupposes" is basically the same thing as "assumes". The idea of aliens means you can't presuppose much of anything... but there you went, assuming a likely lack of many things.

Ha, your assuming this life is based on lipids, amino acids, and nucleotides. This is the error that limits your vision of alien life. When supposing aliens, you need not resort to those building blocks. I personally presuppose that carbon runs the show based on the laws of physics, but I find it hard to justify making the assumption, as you do, that this alien life MUST use the exact building blocks you have listed.

Strawman argument.

I was not saying I assume alien life would neccessarily be based on that. I was just saying, hypothetically, that alien life that uses it could well exist. This was an argument against your statement "cellular life that utilizes DNA would hardly even be worth considering an alien"

An independent genesis of life on another world would be alien, regardless of whether or not its basic building blocks are similar to our own.

To claim otherwise implies you don't understand how common all Earth life is at levels beyond the basic building blocks.

Adenosine is in so many biological pathways? all the basic metabolic pathways are very similar and use very similar enzymes.

Alien life could still have very different metabolic pathways, using completely different enzymes, it may not even have adenosine at all... yet it could still use DNA, lipids, amino acids (probably not even the same 20, and then there is chirality to consider).

Things could still be very very alien, even if they have DNA.

Even if we did find life like that, imagine we actually do discover life so amazingly similar to us as that: At that point which is more likely, that our exact biology propped itself up with the exact same characteristics thru a completely alien abiogenesis event

^ more proof that you don't understand how common all Earth life is at levels beyond the basic building blocks, and how amazingly different such life could be even if it has DNA, lipids, and amino acids (the latter two being very widespread cosmically speaking, and the building blocks of the 1st also being widespread)

[Malokin]

What are you talking about? Where did you get this idea of automatic assumptions of high mutation rates? What are you talking about with human cloning?

This is just one of the criticisms used to make the assertion that cloning with mutation cannot possibly replace the functions of sexual reproduction. Let me the reason you think such a system can't compete, and I can address it. As far as the human cloning bit, I'm saying you can't introduce the argument of a lack of variation or a lack of mutation as reasons why "cloning" as you called it cannot be a working reproductive method. You are introducing flaws in this system that exist for human cloning, but not "cloning" as a reproductive method.

No it doesn't. Otherwise you would expect almost everything to be sexually reproducing. There was nothing innate in the DNA sequence of the LCA that favored ....

When you talk about the "same beginning DNA", you are ignoring that the a series of mutations in organisms that resulted in sexual reproduct, occured in organisms with orders of magnitude longer DNA sequences than the LCA, that were already highly diverged.

Why would you necessarily expect all life to be sexually reproducing just because all of the ingredients to create a sexually reproducing system are present in the origin creature? Some organisms, although they have all the genes that could easily be muted to form a sexually reproductive system, might choose a non sexually reproductive system. Let's use another thought experiment to illustrate this, if I give 1000 chefs all the ingredients to make a cake plus a few odds and ends, many of the chefs will make a cake, but not ALL of them. The likelihood of cake is greater because all of the ingredients required for it are present, BUT this does not mean ALL chefs MUST make cakes, other recipes exist that would inevitably be made. How can you argue that a sexually reproductive system is not likely to emerge, considering you already know it evolved "independently" in multiple instances?

No, its not. We only see convergence when external factors dictate it. If there is an alien world with things swimming in a liquid ocean, they will adopt a hydrodynamic shape, as fish did, as icthyosaurs did, as marine mammals did. Its not because of starting DNA that they adopt hydrodynamic shapes.

Really, is a sea sponge hydrodynamic? What about oceanic plantlife? This is exactly what I'm talking about, the parent organism of all of the hydrodynamic creatures had certain techniques for staying alive that ultimately resulted in the traits that they developed down the line. Being hydrodynamic enough for movement is an improvement on a set of techniques that already exist. If you have a mouth (the gene setup for a mouth) then growing fins to manuevuer your mouth to food is advantageous, as is growing arms, suction filters, etc. If your a plant, or an organism with no mouth, you don't need hydrodynamics to continue your lineage. You make improvements on the techniques already present in your genetics rather than shifting from an animal into a plant. The genes of the ancestor dictate the genes of the offspring because of the ancestor commitment to a strategy, it's unlikely, possibly impossible, to completely switch strategies in the middle of your lineage. This is precisely why animals don't shift into plants, plants haven't all begun growing wings and feet and it's precisely why life on earth doesn't take a shot at trying non-sexually reproducing strategies for passing on their lineage. If their great grandparent had never hunted and consumed other organisms on a cellular level, but instead developed a way to convert sunlight into energy, then perhaps the offspring wouldn't need movement, or hydrodynamics for movement to live.

Likewise, as organisms grow more complex, the allowable mutation rate grows smaller and smaller. This has nothing to do with DNA sequence, or even DNA, but is intrinsic to any system with discretely heritable units.

No, the mutation rate is steady, unless you express the mutation rate of the total genetic "data" within an organism. If I have 10 genetic data units, and the rate of change is 1 per generation, then the total percentage change is 10%, if I have 100 genetic data units and the rate of mutation is still 1 per generation, then I have 1% percent mutation. The rate of mutation is steady, the complexity of the organism is what got larger.

Yet organisms still need to adapt and change, so variation is needed. Thus you need recombination, where variations can be indicidually naturally selected, and combined...

You don't necessarily need recombination to facilitate the adaptation and variation, there could be other techniques that accomplish these prerequisites for evolution. You assume hammers are the only thing that can drive metal into wood, because you come from planet hammer. We're theorizing screwdrivers, not arguing the merits of hammers from other planets.

And here we get to another limit of comple organisms - sometimes when you change "the blueprint" of something that is too complex, You have to build it again from scratch, not modify a previous iteration.

Also, its not clear which combination of the variations is even best, so you'll want to make multiple combinations, and test each one -> ie new organisms with that genetic combination - ie sexual reproduction.

I'll note that many organisms can switch between sexual and asexual reproduction. Some only switch to sexual reproduction when stressed... ie when their current genome isn't quite cutting it, they try out new variations.

This principle is inherent, it is not specific to DNA or sequences of life on Earth.

That is why it is likely to occur in complex aliens.

It all sounds great, but to argue that this is how aliens from planet X MUST function because things here function like that is just silly. Screwdrivers? Thats impossible! How can rotation generate enough force to put the metal into the wood? Blasphemy!

"data" is equaly bad, just stick with "heritable unit".

I don't like that either because it assumes the same grandfather>father>son setup as we have on earth. There is no reason why alien life has to stick to a sequential system like that. Perhaps every organ of an alien could be like our lifeforms, reproducing near death. When an alien defeats a foe, he could coopt the organs of his rival into himself when advantageous. Hell, we're assuming forms of life that rot and die like our forms of life here on earth do. Perhaps a species of alien, although they die, could return from death. A brain slug organ from far down the evolutionary line crawls itself into the long dead body of a dinosaur and beings living, reproducing, and mating with the local populace after millennia of extinction. This is why I wouldn't use "heredity" and why I use such a general term, because heritage describes what we have, and could disclude other styles of reproduction

There are organisms on Earth that live in the conditions you specify, they did not give up their membrane. It is very hard to imagine life becoming very complex without discrete "cell like" units, and compartments to contain metabolic products. "organelles" on a string sounds very much like cells on a string. In fact, many of what we call "organelles" for our life are more properly regarded as endosymbiotic cells.

They didn;'t give up their membrane because they inherited a vestigial membrane from their ancestors. If the ancestor grew up with no membrane, descendants might grow one, but only when the environment dictates that it is required. In my example, the organelles I describe are not enclosed, they themselves are a sort of series of biological systems on a string. But yes, much like people theorize michochandria may be an ancient symbiotic bacteria, so also would my "string-slugs" attach other "string-slugs" to their master reproductive genetic string the same way we may have absorbed the midochandria so long ago. I'm disputing the need for a cellular covering, not the origins of organelles, some of which certainly are not re-purposed bacteria.

Yes, it does. Sure is easy to make baseless assumptions.[/quote[

Yes, it is easy to make such assumptions, you are the one doing it.

I was attacking the way you respond to something by saying "No, it doesn't" without explanation. If your argument is "nuh-uh" you are easily refuted by the unbeatable and infoulable "ya-huh" argument.

I quote: "The idea of aliens presupposes a likely lack ".....

"presupposes" is basically the same thing as "assumes". The idea of aliens means you can't presuppose much of anything... but there you went, assuming a likely lack of many things.

Um...Yeah? The very idea of aliens presupposes they are different from us. Thats why they are aliens. If they are just like us, they really aren't aliens, more like dopplegangers.

I assume aliens are drastically different from us, you assume they are biologically near identical in function down to the cellular level. Who's more absurd here?

Strawman argument.

I was not saying I assume alien life would neccessarily be based on that. I was just saying, hypothetically, that alien life that uses it could well exist. This was an argument against your statement "cellular life that utilizes DNA would hardly even be worth considering an alien"

Please excuse me, I never meant to strawman you. But I simply don't understand how you think that a cellular configuration, DNA, and sexual reproduction could arise from ingredients so vastly different from our own. Wood makes a great house, just not when you stack it up and glue it together like you can with stones.

Does it not stand to reason that if the things you listed are not the building blocks, that perhaps other techniques than cells, dna, and dimorphism might be equally effective for facilitating evolution?

An independent genesis of life on another world would be alien, regardless of whether or not its basic building blocks are similar to our own.

Right. I admit: if humans land on a spaceship they are still aliens even if they are identical to us right down to the DNA. I agree with you but only because are trapping me with a technicality rather than admitting that they are humans and not really what we would usually consider aliens.

To claim otherwise implies you don't understand how common all Earth life is at levels beyond the basic building blocks.

Adenosine is in so many biological pathways? all the basic metabolic pathways are very similar and use very similar enzymes.

Alien life could still have very different metabolic pathways, using completely different enzymes, it may not even have adenosine at all... yet it could still use DNA, lipids, amino acids (probably not even the same 20, and then there is chirality to consider).

*Sigh* But can't you understand that they may not have DNA, lipids, or amino acids AT ALL?

Why must you again draw up a vision of an alien with completely different building blocks, and then ruin it by assuming it somehow forms the same types of larger organic structures that make up our lifeforms? Can't you possibly imagine completely alien building blocks, completely alien biological micro-structures, and completely alien methods of reproduction? This is why I think you have a narrow view of things. How can you possibly argue that the most likely structures to arise out of completely different ingredients will be the same ones that we already have? I never proposed it is impossible for these things to form out of different beginnings, I just purpose that it is far more likely that other, different structures and techniques would form than those we observe based simply on the difference in properties of the originating ingredients.

[trekkie_]

I expect alien life to be similar in functions to earth life (even if they don't physically resemble earth life), especially if it is based near the same environment. That doesn't necessarily mean earth life of today, because a lot of things have long since died out that you could consider to be alien, and their evolutionary paths never bore any fruit for one reason or another. What we do know, is that earth life has developed naturally, under the physics of the universe. So it's safe to assume those same physics can cause similar life to appear elsewhere.

Now, there are a lot of catches, such as life forming with a different base than carbon. But we already have found non carbon based life forms on earth, and they are still similar to the rest of life on earth in how they operate. Even non-DNA based life could still follow the same basic processes.

I'm not sure how else life could develop and reproduce in any different methods than earth life follows, even if it's based on a different process with different bases. the only way of reproducing that life on earth doesn't already do, is for some organism to inject a third party organism and mutates its genetics to either recreate itself or create a new type of organism. But obviously, you'd need a third party organism to begin with....and you won't have that if you're the first form of life developing.

You could argue that things like virus's already do basically that, but technically virus's aren't alive. Anything else, and it'd either be a poof-into-existence reproduction (seemingly impossible) or a mechanical reproduction. It may be possible that there is life that essentially mechanically 3d prints itself naturally to reproduce on a large scale....but technically, life on earth already does that on a small scale.

Edited December 13, 2014 by trekkie_

[KerikBalm]

But we already have found non carbon based life forms on earth

No we haven't, where did you get this tripe?

[KerikBalm]

Why would you necessarily expect all life to be sexually reproducing just because all of the ingredients to create a sexually reproducing system are present in the origin creature?

#1) I wouldn't, but you said: "convergence is not just possible but actually highly likely." and "stand to reason you end up with similiar convergent mutations when you start with the same beginning dna"

I disputed tat, proof by contradiction.

#2) All the "ingredients" for a sexually reproducing creature were not present in the LCA, they came later.

If you are going to claim that just because they descended from the LCA, that the LCA had the capability... then I'm going to go ahead and use your logic to say Pikaia had the capability to build Saturn Vs and go to the moon.

Really, is a sea sponge hydrodynamic? What about oceanic plantlife?

Nope, and neither of them actively swim.

Strawman argument.

No, the mutation rate is steady

No it is not.

I was attacking the way you respond to something by saying "No, it doesn't" without explanation. If your argument is "nuh-uh" you are easily refuted by the unbeatable and infoulable "ya-huh" argument.

What a load of BS.

When you say something that is factually wrong (see the mutation rate tripe above), when you make a completely unsupported assertion, a "Nuh-uh" is all it takes.

The burden of proof is on you.

Um...Yeah? The very idea of aliens presupposes they are different from us.

I will give you that it does presuppose that they are different in *some way*. But you claim *specific*, qualitative differences, and that is a completely unsupported assertion.

I assume aliens are drastically different from us, you assume they are biologically near identical in function down to the cellular level. Who's more absurd here?

You are with your continuous strawman arguments, or else you lack the comprehension neccessary to understand that simply being membrane enclosed, using lipids, amino acids, and nucleic acids is not sufficient to be "near identical in function down the the cellular level" - not even the subcellular level.

I suggests a huge ignorance of the complecity of cells. You could have DNA playing some role, without it even being the carrier of heritable traits. It could be forming complexes with RNA, to produce more complex ribozymes in place of our protein enzymes (granted, we do have some examples of RNA enzymes, and RNA-protein hybrid enzymes, but no DNA-RNA ribozymes as far as I know) the amino acids could be being used to form PNA, which could be the heritable units. It could exist in a non-polar solvent, and the lipid membrane could be inverted from what we see in our cells.

Things could be almost completely different. But if it is carbon based at all, you are likely to see various classes of organic molecules appearing.

Please excuse me, I never meant to strawman you. But I simply don't understand how you think that a cellular configuration, DNA, and sexual reproduction could arise from ingredients so vastly different from our own. Wood makes a great house, just not when you stack it up and glue it together like you can with stones.

See above, DNA itself would be the same "ingredient" (but the nucleotide bases could be different).

A cellular configuration, as above could easily arise with lipids in a non-water solvent. Additionally, ammonia could probably be a suitable solvent for life using DNA, lipids, amino acids , etc, as well.

Sexual reproduction could easily occur in an organism that doesn't have DNA. Its a very good way to get higher variation with a low mutation rate.

Right. I admit: if humans land on a spaceship they are still aliens even if they are identical to us right down to the DNA. I agree with you but only because are trapping me with a technicality rather than admitting that they are humans and not really what we would usually consider aliens.

Down to identical DNA sequence - like prometheus (what a crap movie) -yea they'd be humans.

I never specified identical DNA. I simply specified that they had DNA. Our DNA has ATCG - theirs may not.

Our DNA encodes genes - theirs may not, theirs may just act on basepairing principles to function somewhat like like our v-snare and t-snare proteins.

They could be very alien, and still have DNA.

*Sigh* But can't you understand that they may not have DNA, lipids, or amino acids AT ALL?

Strawman again. I'm not saying such life coulding exist, I was disputing your

FOR THE SECOND TIME: This was an argument against your statement "cellular life that utilizes DNA would hardly even be worth considering an alien"

Why must you again draw up a vision of an alien with completely different building blocks, and then ruin it by assuming it somehow forms the same types of larger organic structures that make up our lifeforms?

What? I was envisioning an alien with the *same building blocks* that operate *very differently* to dispute your statment "cellular life that utilizes DNA would hardly even be worth considering an alien"

Can you understand this yet, or do I need to repeat it a third time?