Should we expect alien life to have DNA ??

[Just thinking]

Well, that's pretty much my question -- should we expect extraterrestrial life (when found) to contain DNA or some similar equivalent? Any thoughts?

[Terry]

something equivalent would be my guess.

[Wings]

Well, I suppose I would have to ask if DNA or a similar equivalent is necessary for certain stages of development in life?

[Jeff Corey]

Some equivalent to guide reproduction. But not really like DNA as we know, if were a silicon rather than carbon based life form, for example.

[mhaze]

Life must replicate?

[Jeff Corey]

Life must replicate?

Good point. Some life forms might not. They could just somehow evolve and then not reproduce. That probably happen with most mutations.

[ThatSoundAgain]

They might have engineered themselves to be immortal and sterile. But to get to a point where they could do that, they'd have to evolve (and therefore reproduce and die).

Disclaimer: I am of limited imagination.

[strathmeyer]

They're made out of meat!

[cyborg]

Some equivalent to guide reproduction. But not really like DNA as we know, if were a silicon rather than carbon based life form, for example.

The chemistry of silicon would tend to preclude that - it just doesn't form nice and stable complex chemicals like carbon does and that would be a must for forming any complex piece of machinery.

As such I would think it highly unlikely to expect to see any lifeforms that would naturally arise to not utilise carbon compounds heavily in their construction - it's just so versatile.

ET may well use DNA simply because it is a known proven mechanism for providing blue-prints for constructing machines based on organic chemistry. Any alternative proposals would have to provide a mechanism of similar power in order to be plausible.

They might have engineered themselves to be immortal and sterile.

I would imagine that any creature that found itself in the position where it is immortal and sterile would be fairly vulnerable to being made extinct by simply being damaged. The fact that mortal and reproductive organisms would out-compete them would not help either.

[Dan O.]

In other threads there has been talk about the development of AI machines to explore the stars because it is too far for humans to make the journey. These machines would need to have self repair facilities which could probably include replication of the entire system from the stored blueprints. At what point does AI become sufficiently advanced to be called "life"? And if we discover such an alien probe would that count as an alien life form?

[UserGoogol]

Life must replicate?

In principle, I suppose it might be possible for there to be a world where abiogenesis is simply extremely common, and "natural selection" would happen in this world simply by the organisms which live longer lives (or are easier to appear spontaneously) being more common than the organisms which live shorter lives. Such a form of evolution would undoubtedly be vastly less powerful than reproductive natural selection, but it might be powerful enough to produce something just complex to be considered a very simple form of life.

Although personally, I think that the word "life" should imply some sort of reproduction, (since reproduction is such a fundamental part of life on Earth) but that's just a pedantic question.

[cyborg]

At what point does AI become sufficiently advanced to be called "life"?

Whenever it pleases us to do so. Really it's just another type of machine; it's a classification. There's nothing intrinsically special about the machines we call life-forms that imbues the term life with magical power.

[mhaze]

In principle, I suppose it might be possible for there to be a world where abiogenesis is simply extremely common, and "natural selection" would happen in this world simply by the organisms which live longer lives (or are easier to appear spontaneously) being more common than the organisms which live shorter lives. Such a form of evolution would undoubtedly be vastly less powerful than reproductive natural selection, but it might be powerful enough to produce something just complex to be considered a very simple form of life.

Although personally, I think that the word "life" should imply some sort of reproduction, (since reproduction is such a fundamental part of life on Earth) but that's just a pedantic question.

Yes, it occurred to me when I asked the question, that a reasonable definition of "life" would include reproduction/replication. But for example, we have several scenarios of computers becoming aware, then adding banks of computational and memory circuits to themselves. Is there still only one machine? At some point the question has no meaning. If a conscious "thing" arose on the Internet, could we figure out if there was one or several? By what standards?

Obviously, these are avenues of "growth" that do not follow the rules of biological reproduction as we know them.

[DRBUZZ0]

The one thing I would expect from life from another planet is that it would be organic in chemistry. I realize that might be narrow and it does not necessarily have to be true, but carbon based compounds are capable of forming complex structures in manners which inorganic compounds generally cannot.

There are also more carbon-based chemicals known than all inorganic chemicals. carbon and hydrogen are both relatively common and other elements do not have the tendencies to react as readily.

Of course, it's possible that "life" could evolve into a sort of technological-electronic or similar based intelligence, but I would expect it would at least start out from a basis that is organic..

[The Atheist]

Well, that's pretty much my question -- should we expect extraterrestrial life (when found) to contain DNA or some similar equivalent?

No.

I think that we should make no assumptions about extraterrestrial life, because all assumptions will see ET anthropomorphisised. We will assume it needs water, has a replicating nucleus base, reproduces, has feelings and thinks.

We could be completely wrong.

[DRBUZZ0]

No.

I think that we should make no assumptions about extraterrestrial life, because all assumptions will see ET anthropomorphisised. We will assume it needs water, has a replicating nucleus base, reproduces, has feelings and thinks.

We could be completely wrong.

I disagree. We know life can exist with water and in certain temperature constraints and such. Yes, perhaps it could be entirely different, but if we are going to look for life the best chance for success would probably come if we pick places which have the sort of factors which we have already established can support life.

Until we find something else, we have only one sample of a life-bearing planet. That's crappy statistically, but it's all we've got as an example. So ones which are similar would be the logical place to start...

[Schneibster]

Well, that's pretty much my question -- should we expect extraterrestrial life (when found) to contain DNA or some similar equivalent? Any thoughts?Not necessarily, but more than likely. Some equivalent at least. DNA itself may be a nearly optimal solution for our chemistry, but it's almost certainly not the only solution. Other similar solutions might work better under different circumstances.

[T'ai Chi]

We'll find them with DNA.

They'll also all speak English and have two arms and two legs and a head. Their food will only be minor variants of ours, typically just colored brighter. Just like on Star Trek.

[Wolfman]

We'll find them with DNA.

They'll also all speak English and have two arms and two legs and a head. Their food will only be minor variants of ours, typically just colored brighter. Just like on Star Trek....and they'll all dress in skimpy clothes, and the women will all be buxom babes who are borderline nymphomaniacs.

But Kirk also ran into beings that were made out of plasma, or other such exotic things...a plasma being would not have DNA, I'd assume.

[Jeff Corey]

...and to differentiate them from humans, they will have different foreheads or ears or both.

[Paul C. Anagnostopoulos]

Yeah, I noticed that too, Jeff. How come they never have slightly different sex organs?

~~ Paul

[cyborg]

Well there was that episode where Riker had to escape a pre-warp civilisation by having sex with an alien played by Bebe Neuwirth (First Contact, not the film) where Riker notes they don't exactly do things the same way but she's still enthusiastic all the same (pretty perverted if you ask me).

Oh and in Star Trek VI: The Undiscovered Country there is that alien that Kirk kicks in the knee - which is actually where its sex organs were.

[DRBUZZ0]

...and they'll all dress in skimpy clothes, and the women will all be buxom babes who are borderline nymphomaniacs.

But Kirk also ran into beings that were made out of plasma, or other such exotic things...a plasma being would not have DNA, I'd assume.

Yeah, but we don't care because you can't make out with plasma... (wait... can you?)

[Wolfman]

Yeah, but we don't care because you can't make out with plasma... (wait... can you?)
If anyone could do it, it would be Captain James Tiberius Kirk

[Just thinking]

I disagree. We know life can exist with water and in certain temperature constraints and such. Yes, perhaps it could be entirely different, but if we are going to look for life the best chance for success would probably come if we pick places which have the sort of factors which we have already established can support life.

Until we find something else, we have only one sample of a life-bearing planet. That's crappy statistically, but it's all we've got as an example. So ones which are similar would be the logical place to start...

I tend to agree with the water element of your argument, at the very least. It's a great solvent and vehicle for many nutrients and components.

[The Atheist]

I tend to agree with the water element of your argument, at the very least. It's a great solvent and vehicle for many nutrients and components.

But what about the one in the Pleiades where they're use beer instead of water as the basis for life. You don't want to go there? Even for a visit?

[petra10]

I expect they will have DNA or at least something simular.Does all life forms on earth have DNA, for instance does bacteria have it?

[Schneibster]

I expect they will have DNA or at least something simular.Does all life forms on earth have DNA, for instance does bacteria have it?Yep. There are a few living things that use a variant base; and a few that use a different mapping of one or two trios of bases to an amino acid; but neither of those would make it "not DNA" from the point of view of most molecular biologists.

[JoeEllison]

Jeez... we can't really expect anything, at all.

[petra10]

So i guess that means anything alive, even aliens , must have some sort of DNA.I imagine in all of the universe aliens will take many lifeforms,some of which I am sure we cannot imagine.

[Jeff Corey]

Yeah, I noticed that too, Jeff. How come they never have slightly different sex organs?

~~ Paul
Well there are the Ferengi ("foreigner" in Hindi) who have huge ears, foreheads, skulls which imitate big brains, and you ever see their wimmin?
Since the Ferengi evolved such huge brainy heads, the wimmin must have huge infant delivery capacity. Extremely wide hips and associated package.
The male Ferengi must, correspondingly, have huge schwantzstuckers.

[Wowbagger]

If this hypothetical alien life-form is the product of natural selection, there would have to be something for nature to select from.
On Earth, the ultimate focus of selection is on genes, and the DNA strands that make them up.
For extra-terrestrial aliens, it could possibly be something else, roughly equivalent in "purpose", but entirely different in construction.

It could be possible such "different" targets of selection are emerging, on this very planet, possibly in the form of memes, for example.

If the aliens are not a product of natural selection, then who knows?!

[The Atheist]

If the aliens are not a product of natural selection, then who knows?!

Zem?

[geni]

I suspect not. I would be somewhat suprised if there was only one carbon based way of producing life.

For chemical based life I suspect pretty much everything would be carbon based.

[JoeEllison]

For chemical based life I suspect pretty much everything would be carbon based.
Suspect? Yeah, fair enough. But to "expect" it? Not so much. Assuming that the laws of physics are the same everywhere, we should certainly give carbon-based life-forms a higher weight.

On the other hand, mention has been made of "second generation lifeforms", those that started out "naturally", and then subjected themselves to certain "alterations", or the creations of biological beings.

So, really, who can say?

[Dan O.]

And if we are going to speculate on a second generation life form why not a third generation perhaps based on pure energy (but of course, Star Trek already covered that).

[JoeEllison]

And if we are going to speculate on a second generation life form why not a third generation perhaps based on pure energy (but of course, Star Trek already covered that).That's sort of the problem of speculating on a situation that could have had a billion years to develop, isn't it? Any "life-form" we encounter could be several significant stages away from the biological forms we are used to. Therefore, our expectations are meaningless.

[Taffer]

No.

The only important thing to life is that, IMHO, it is a system which encodes the neccissary information for its own replication.

[Big Al]

DNA-controlled reproduction is such a sophisticated and efficient system, with self-correction and inbuilt redundancy, that it shows all the signs of having been subjected to billions of years of natural selection (DNA, ribosomes, tRNA, mRNA, the whole bit, not just animals built from it). Not to sound too much like a creationist, I hope, it seems unlikely that DNA synthesis started off like this.

It's such a good system that every living thing on the planet has it: I don't think it's the only game in town, it just won out during early self-replication wars. It's the only survivor of possibly a nuimber of related systems.

One thing I've often wondered about: are multicellular constructions and bilateral symmetry necessary or advantageous features? Or do we just have them because of a cell division error aeons ago, where two single cells failed to separate? The symmetry aspect seems to indicate partial cell separation.

Bacteria (arguably the most developed lifeforms on the planet) do just fine with one cell, asexual reproduction (with occasional cell conjugation) and no symmetry.

[cyborg]

There are obvious advantages to living as a colony of cells (which one could view any multicellular organism as but which also includes less traditional ones such as amoeba colonies that act coherently together) rather than an individual - co-operation vs competition.

I cannot see any obvious advantage to bi-lateral symmetry per-se but in animals that select sexually a lack of symmetry often indicates genetic weakness and hence makes the selection of symmetrical organism more likely.

[Schneibster]

I would argue that bilateral symmetry is a consequence of the evolutionary superiority of redundancy. Since energy, time, and materials are required for it, it is also the minimal configuration that provides that redundancy; thus the most efficient. Just my musings.

[Beerina]

They're made out of meat!

"Ugly bags of mostly water."

[Beerina]

I would argue that bilateral symmetry is a consequence of the evolutionary superiority of redundancy. Since energy, time, and materials are required for it, it is also the minimal configuration that provides that redundancy; thus the most efficient. Just my musings.

Either that or it's an easy thing to accomplish with DNA and our particular chemicals that control growth. Bilateral, as well as longitudinal via arms and legs being basically a copy of each other, now heavily modified. Starfish might wonder about the glories of 5-sided symmetry. Millipedes about "thousand"-fold longitudinal symmetry.

[Schneibster]

Either that or it's an easy thing to accomplish with DNA and our particular chemicals that control growth. Bilateral, as well as longitudinal via arms and legs being basically a copy of each other, now heavily modified. Starfish might wonder about the glories of 5-sided symmetry. Millipedes about "thousand"-fold longitudinal symmetry.You got a point. On the other hand, longitudinal symmetry could be argued to be due to the need both to propel, and steer. :D

[Taffer]

Either that or it's an easy thing to accomplish with DNA and our particular chemicals that control growth. Bilateral, as well as longitudinal via arms and legs being basically a copy of each other, now heavily modified. Starfish might wonder about the glories of 5-sided symmetry. Millipedes about "thousand"-fold longitudinal symmetry.

Don't forget, some of the organisms during the cambrian explosion were really weird. REALLY weird.

I suspect that what we see is just the result of one body plan which happens to work well. I suspect greatly that there are others.

[Schneibster]

Don't forget, some of the organisms during the cambrian explosion were really weird. REALLY weird.

I suspect that what we see is just the result of one body plan which happens to work well. I suspect greatly that there are others.Considering arachnids and insects, I suspect you're right, in terms of longitudinal symmetry. An example lacking bilateral symmetry, however, is more difficult to find.

[blutoski]

Starfish might wonder about the glories of 5-sided symmetry.

Just a point of interest: starfish (and the rest of this phylum, including basket stars, sea cucumbers, sand dollars...) have a type of bilateral symmetry called "pseudopentaradial". Flip one over, and you'll find only one madreporite.

In terms of whether ET will have DNA... doubtful. The current models of terrestrial abiogenesis don't require or even expect DNA. It appears to be a later archival development, and my guess is that another archival system would be adequate. Fifty years ago, a protein archive was considered quite plausible.

Having said that, now that we've found martian meteors on Earth, there's a smidgen of a chance that panspermia is credible, even if not a terrestrial explanation. That slighly increases the chance of finding nucleic acids on other biomes in my opinion.

I would say that the chance of them having the same nucleic acids is pretty slim, and even if they did, the codons would be different, and even if they were the same, I can't imagine them coding for the same amino acids. Even here on earth, some kingdoms code for different amino acids.

My question is: would ET taste like chicken?

[Schneibster]

I have to point out that proteins made from different amino acids would not be "protein" from the point of view of our biochemistry; we do not have the molecular machinery to process amino acids other than the twenty DNA codes for as protein. We might be able to use them for energy, but not for building material.

Of the twenty amino acids our particular use of the genetic code permits us to use to create proteins, we manufacture twelve; the other eight we require a supply of on a regular basis. We might be able to construct the twelve from "alien" amino acids; I don't know enough biochemistry to comment on that. But those eight we cannot construct, we must obtain from our food, and if we don't get them we will die.

[Just thinking]

... My question is: would ET taste like chicken?

On that, you'll have to take the first bite.

As for advantages of bilateral symmetry, my guess is that it allows more complex organisms to have equal freedom of movement and detection for attack and defense. Maximizing their ability to see, evade, grasp and whatever else they use to survive in harsh environments.

[Big Al]

I have to point out that proteins made from different amino acids would not be "protein" from the point of view of our biochemistry; we do not have the molecular machinery to process amino acids other than the twenty DNA codes for as protein.

There are more than twenty triplet codons. Most, if not all, of the available amino acids have several similar codons (http://algoart.com/aatable.htm): this allows single-base transciption errors to be tolerated.

Yet again, real life is so much more fascinating than the creationists' sterile, static imaginings.

[Schneibster]

There are more than twenty triplet codons. Most, if not all, of the available amino acids have several similar codons (http://algoart.com/aatable.htm): this allows single-base transciption errors to be tolerated.There are indeed. There are "START" and "CUT" and multiple codons for the same instruction. Overall, it could be an 8-bit instruction set, with sixty-four instructions, but it actually only has twenty-one instructions. (One of the instructions, AUG, codes both for START and for methionine. Note also that it is both the only code for START, and the only code for methionine; therefore, all proteins we synthesize directly from DNA begin with methionine.)

Yet again, real life is so much more fascinating than the creationists' sterile, static imaginings.I assume you didn't intend this as a response to me; if you did, you've misjudged me egregiously. But on the basis of my assumption, yes, I'd have to agree with you.

[mhaze]

I have to point out that proteins made from different amino acids would not be "protein" from the point of view of our biochemistry; we do not have the molecular machinery to process amino acids other than the twenty DNA codes for as protein. We might be able to use them for energy, but not for building material.

Of the twenty amino acids our particular use of the genetic code permits us to use to create proteins, we manufacture twelve; the other eight we require a supply of on a regular basis. We might be able to construct the twelve from "alien" amino acids; I don't know enough biochemistry to comment on that. But those eight we cannot construct, we must obtain from our food, and if we don't get them we will die.

Well....If just one of the amino acids was mirrored the wrong way, it would be totally useless.

To put it simply, we aren't going to another star finding food, and nothing from elsewhere is going to come here and eat us.

That is, not unless DNA goes back way farther and has a totally different method of genesis than what we consider currently. And that's really too much of a stretch, isn't it. Without some sort of collaborating evidence like radio signals, or whatever.

[Taffer]

Considering arachnids and insects, I suspect you're right, in terms of longitudinal symmetry. An example lacking bilateral symmetry, however, is more difficult to find.

Some of the creatures in the cambrian explosion were exhibited radial symmetry, if memory serves.

[Big Al]

I assume you didn't intend this as a response to me; if you did, you've misjudged me egregiously. But on the basis of my assumption, yes, I'd have to agree with you.

It's OK. Schneibster: I know you're not a wooster. I really was just marvelling at how fantastic the world is, the more you learn about it.

I really do find the whole protein synthesis system absolutely astounding, without the need to invoke God, Oz or Mithras as an explanation ('cause they aren't explanations at all). One thing seems plain to me: DNA was not the first replicator, just the winner of a long line of competitors.

RNA is a plausible precursor to DNA, but I've heard some interesting theories for the first in the line. I seem to remember a guy called Cairns positing organic-molecule-concentrating clays as the first replicators.

It's so great to have unanswered questions which may one day be answered, instead of having to accept "Because God made it so" as the answer to everything.

[Big Al]

To put it simply, we aren't going to another star finding food, and nothing from elsewhere is going to come here and eat us.

I've always found the "unstoppable alien plague" film cliché hard to swallow. Natural selection is all about offence and defence developing in parallel: a bug learns a bit more about our immune system and vice versa. In the end, you have a bug that's fantastically good at getting on board, and an immune system that stops it from killing us.

An alien bug wouldn't stand a chance, because it would lack the tricks necessary to weasel round our immune system. It wouldn't be remotely adapted to us. On the other hand, our leukocytes are red-hot at saying "You are not of the body!" and gobbling up stangers. The immune system would NOT have to be adapted to the bug.

[INRM]

I think it would better to forgo sending self-replicating AI machines out into space, and just wait until we can send a manned mission.

Even in the sixties we could have sent a machine to the moon, but we didn't and send a manned vehicle there instead. As Kennedy said "Not because it is easy, but because it is hard!" -- and yes I'm quoting authority, but I happen to agree with him.

Ton'

[Schneibster]

Some of the creatures in the cambrian explosion were exhibited radial symmetry, if memory serves.Some do today. Starfish are a good example. So are sea cucumbers.

[Schneibster]

It's OK. Schneibster: I know you're not a wooster. I really was just marvelling at how fantastic the world is, the more you learn about it.Good; there has been a running conversation that could have led you to this erroneous view, so I did feel the need to make sure.

I really do find the whole protein synthesis system absolutely astounding, without the need to invoke God, Oz or Mithras as an explanation ('cause they aren't explanations at all). One thing seems plain to me: DNA was not the first replicator, just the winner of a long line of competitors.I think that some very specific characteristics of DNA and the protein synthesis machinery associated with it caused it to outcompete other methods. Which is basically saying the same thing.

RNA is a plausible precursor to DNA, but I've heard some interesting theories for the first in the line. I seem to remember a guy called Cairns positing organic-molecule-concentrating clays as the first replicators.I have heard these competing hypotheses as well. Have you read Stuart Kaufman's At Home in the Universe? He has yet another idea. Or perhaps it's arguably a precursor to something like this. Interesting, in any case.

It's so great to have unanswered questions which may one day be answered, instead of having to accept "Because God made it so" as the answer to everything.That's the primary reason I reject religion; that's always ultimately the answer to everything, if you push far enough. I don't do well with "Because I said so." It irritates me.

[mhaze]

I've always found the "unstoppable alien plague" film cliché hard to swallow. Natural selection is all about offence and defence developing in parallel: a bug learns a bit more about our immune system and vice versa. In the end, you have a bug that's fantastically good at getting on board, and an immune system that stops it from killing us.

An alien bug wouldn't stand a chance, because it would lack the tricks necessary to weasel round our immune system. It wouldn't be remotely adapted to us. On the other hand, our leukocytes are red-hot at saying "You are not of the body!" and gobbling up stangers. The immune system would NOT have to be adapted to the bug.

Well... to carry that a bit farther, an alien bug might not even recognize us as a target, but instead, would gobble up all the paint on buildings....or maybe gobble up all the tires on cars...:)

Alien actually, really does mean alien, is what that says, albeit poorly.

[blutoski]

Some do today. Starfish are a good example. So are sea cucumbers.

Again: echinodermata are pseudo-pentaradial. Their body plan is ultimately based on bilateral symmetry. You have to draw the saggital section through the one madreporite.

(I lived with an oceanographer and helped her with research for a couple of years - she never got tired of reminding me that the juvenile stage is obviously bilaterally symmetric, and the mature pentaradial body plan is sort of an illusion, not to be confused with authentic radialians.)

What you're looking for is called the 'radialians': choanoflagellatta, porifera, placazoa, cnidaria, ctenophora. Pretty much all the other animalia kingdom phyla are bilateria.

In any case, the point is that radialians are still pretty successful: sponges and sea anemones being good examples. The relative success of bilateria could be coincidental. Radialians are certainly the predecessors of bilateria, and held their own for perhaps a billion years.

[Wowbagger]

Zem?
No, I am quite certain the creatures of Squornshellous Zeta are also the product of natural selection.

[Schneibster]

Again: echinodermata are pseudo-pentaradial. Their body plan is ultimately based on bilateral symmetry. You have to draw the saggital section through the one madreporite.

(I lived with an oceanographer and helped her with research for a couple of years - she never got tired of reminding me that the juvenile stage is obviously bilaterally symmetric, and the mature pentaradial body plan is sort of an illusion, not to be confused with authentic radialians.)Whoops! Apologies, I missed that post of yours. Having done some poking around, it appears that this description is still somewhat controversial, but gaining adherents. Far be it from me to argue with an oceanographer on an apparently controversial theory within her specialty. That would be borrowing trouble. ;)

What you're looking for is called the 'radialians': choanoflagellatta, porifera, placazoa, cnidaria, ctenophora. Pretty much all the other animalia kingdom phyla are bilateria.

In any case, the point is that radialians are still pretty successful: sponges and sea anemones being good examples. The relative success of bilateria could be coincidental. Radialians are certainly the predecessors of bilateria, and held their own for perhaps a billion years.Not to be offensive, just pedantic, I believe that's radiolarians. Feel free to modify it if there's edit time left, and if I'm correct. The remainder agrees with my sources.

[Just thinking]

Well... to carry that a bit farther, an alien bug might not even recognize us as a target, but instead, would gobble up all the paint on buildings....or maybe gobble up all the tires on cars...:)

Alien actually, really does mean alien, is what that says, albeit poorly.

That was one thing I really liked about Crichton's Andromeda Strain -- it mutated into a form that started eating away gasket material and skin. It also registered 00 on amino acids and a host of other Earth-based life readings, giving the scientists a totally new outlook.

[Corsair 115]

I've always found the "unstoppable alien plague" film cliché hard to swallow...

An alien bug wouldn't stand a chance, because it would lack the tricks necessary to weasel round our immune system. It wouldn't be remotely adapted to us. On the other hand, our leukocytes are red-hot at saying "You are not of the body!" and gobbling up stangers.Does that mean the reverse scenario is also unlikely, i.e. aliens wouldn't be affected by Earth bacteria? So the demise of the Martian invaders in H.G. Wells' The War of the Worlds due to infection from terrestrial germs is highly improbable?

[mhaze]

Does that mean the reverse scenario is also unlikely, i.e. aliens wouldn't be affected by Earth bacteria? So the demise of the Martian invaders in H.G. Wells' The War of the Worlds due to infection from terrestrial germs is highly improbable?

Not highly improbably, but impossible, with the exception being that the "alien" and the earth have a common ancestry. There is no reason to go down that road of speculation when the "alien" is already speculative enough.

Of course, this just ruined a lot of good science fiction....

[sphenisc]

Whoops! Apologies, I missed that post of yours. Having done some poking around, it appears that this description is still somewhat controversial, but gaining adherents. Far be it from me to argue with an oceanographer on an apparently controversial theory within her specialty. That would be borrowing trouble. ;)

Not to be offensive, just pedantic, I believe that's radiolarians. Feel free to modify it if there's edit time left, and if I'm correct. The remainder agrees with my sources.

Just to clarify, the term you're both looking for is 'radiates' from the taxon Radiata. Radiolarians are protozoa, not members of the Animalia.

[Dan O.]

At least in the remake, the martians had been periodically revisiting earth for the harvest and they may have even been responsible for seeding life on this planet in the first place. It would therefor be reasonable to expect the martians to be fully compatible biologically and have no defense against our super-evolved bugs. Similarly, we would not have any defenses against the bugs they brought from home but the movie ended before the smaller population caused a noticeable effect.

[mhaze]

How did you find out our secret?

[dogjones]

Well there are the Ferengi ("foreigner" in Hindi) who have huge ears, foreheads, skulls which imitate big brains, and you ever see their wimmin?
Since the Ferengi evolved such huge brainy heads, the wimmin must have huge infant delivery capacity. Extremely wide hips and associated package.
The male Ferengi must, correspondingly, have huge schwantzstuckers.

Ah, but the Ferengi like it in the ears ("our ears are our most erogenous zone"). So this is clearly where their genital organs are. And their OBs don't use forceps to aid birth; they use really strong Q-Tips.