# Is it legitimate to say that all living things have DNA? **URL:** \ **Category:** Factual Questions\ **Created:** [January 24, 2009, 11:47pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849 "2009-01-24T23:47:11Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![muttrox](https://avatars.discourse-cdn.com/v4/letter/m/a8b319/32.png) [@muttrox](https://boards.straightdope.com/u/muttrox)\ **Post date:** [January 26, 2009, 2:35pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/41 "2009-01-26T14:35:55Z")
> [@cmyk](#): > > It reminds me of a very small line in E.T., when the government is swarming through Elliot’s house, and E.T. is on the bed dying, one of the random scientists exclaims, “He’s got DNA!” I really wonder what the probability for that is. Don’t assume they are independent events. DNA could have traveled between the stars, E.T. and humans could share some ancestry. (I think Freeman Dyson wrote about this, but I may be misremembering.) ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [January 26, 2009, 2:48pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/42 "2009-01-26T14:48:58Z")
> [@Chronos](#): > > And if there is other life out there which isn’t related to terrestrial life, then it probably doesn’t have DNA itself, though it may well have some other molecule which serves the same purpose and works the same basic way. I would say that the chances are actually pretty good that extraterrestrial life might use DNA, or at least RNA, since it is a reasonable solution to the problem of finding a molecule capable of encoding huge amounts of information, and which has a fairly simple way to replicate itself. That’s not to say it’s the _only_ solution to the problem, but I doubt that there are a very large number of them. DNA-based life seems to have developed spontaneously on Earth not long after it cooled enough (if we discount that it arrived from elsewhere), so it is probably not an extremely unlikely event. On the other hand, DNA-based life doesn’t have to use exactly the same nucleotides that it does on Earth, and the details of the genetic code would certainly be different. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [January 26, 2009, 3:02pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/43 "2009-01-26T15:02:15Z")
> [@ftg](#): > > It is quite low which is why there are such simple algorithms to compute it It is low in information _density_. Assuming, as a previous poster noted, the digits of pi follow a normal probability distribution, any arbitrary-length string of digits you care to name **will** be found. Eventually. Now, it may (to make up some numbers) take a nmber of digits equal to the the number or electrons in the Universe raised to its own power before you find even one complete poem, fore example, and that many raised to it’s own power raised to its own power digits more before you find another. But infinite is really, really big. ---
**Author:** ![elucidator](https://avatars.discourse-cdn.com/v4/letter/e/8edcca/32.png) [@elucidator](https://boards.straightdope.com/u/elucidator)\ **Post date:** [January 26, 2009, 4:25pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/44 "2009-01-26T16:25:31Z")
If its true that DNA is the basis for alien life forms, then we can eat them! Downside, of course, is that they can eat us. ---
**Author:** ![brazil84](https://avatars.discourse-cdn.com/v4/letter/b/8491ac/32.png) [@brazil84](https://boards.straightdope.com/u/brazil84)\ **Post date:** [January 26, 2009, 4:30pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/45 "2009-01-26T16:30:30Z")
> [@sweepkick](#): > > Your post reminded me of this article from the old Brunching Shuttlecocks site: > > [Monkeys, Numbers, and You](http://www.brunching.com/randommonkeys.html) > > 😃 Thank you. You might enjoy a short story called “The Library of Babel” written by Borges. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [January 26, 2009, 5:03pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/46 "2009-01-26T17:03:46Z")
> [@Colibri](#): > > [Moderating] > > This is GQ. Since it is impossible to factually demonstrate that non-physical entities are alive, this isn’t an appropriate response to the OP. Please confine religious and spiritual speculation to GD. > > Colibri > General Questions Moderator OK, staying only in the physical realm, so to speak, we really do not know what life really is. People in multi disciplines throughout history have tried to define what life is, none satisfactory, though I have no doubt that many feel science will one day discover what life really is, it is still very much a unknown. So we are left with putting traits to help define life characteristics we observe, one such trait we notice is DNA, but that does not answer the question about life, just answers a question along the lines ‘does things that have DNA always contain DNA’ ---
**Author:** ![brujaja](https://avatars.discourse-cdn.com/v4/letter/b/4af34b/32.png) [@brujaja](https://boards.straightdope.com/u/brujaja)\ **Post date:** [January 26, 2009, 5:08pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/47 "2009-01-26T17:08:40Z")
I read a fascinating book by Guy Murchie called, “The Seven Mysteries of Life”, in which (among many other things) he postulates that given the commonly accepted arbitrary conditions said to constitute “life,” many things would qualify. Among the most interesting of these are crystals. They grow, organize, consume, reproduce, etc. He wasn’t exactly seriously suggesting that they’re alive; but it does give one pause. (I keep thinking of the Crystalline Entity on ST:TNG.) As far as I know, they’re not using tools yet, though. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [January 26, 2009, 5:30pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/48 "2009-01-26T17:30:09Z")
> [@elucidator](#): > > If its true that DNA is the basis for alien life forms, then we can eat them! Downside, of course, is that they can eat us. Skunk cabbage is DNA-based, too, but I suspect you wouldn’t want to eat it. come to that, so is hemlock. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [January 26, 2009, 6:55pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/49 "2009-01-26T18:55:02Z")
> [@Markxxx](#): > > Could you say > > “All living things have DNA, but not all things with DNA are alive?” More like the other way around. Everything of which we are aware that is unquestionably alive has DNA. There are a few examples of things whose “alive/not-alive” status is debatable that do not have DNA. ---
**Author:** ![Todderbob](https://avatars.discourse-cdn.com/v4/letter/t/e47774/32.png) [@Todderbob](https://boards.straightdope.com/u/Todderbob)\ **Post date:** [January 26, 2009, 7:18pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/50 "2009-01-26T19:18:38Z")
> [@Smeghead](#): > > More like the other way around. > > Everything of which we are aware that is unquestionably alive has DNA. > There are a few examples of things whose “alive/not-alive” status is debatable that do not have DNA. And a few things with DNA that have questionable alive/notalive status’. ---
**Author:** ![YamatoTwinkie](https://avatars.discourse-cdn.com/v4/letter/y/cc9497/32.png) [@YamatoTwinkie](https://boards.straightdope.com/u/YamatoTwinkie)\ **Post date:** [January 26, 2009, 8:20pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/51 "2009-01-26T20:20:25Z")
> [@kanicbird](#): > > OK, staying only in the physical realm, so to speak, we really do not know what life really is. People in multi disciplines throughout history have tried to define what life is, none satisfactory, though I have no doubt that many feel science will one day discover what life really is, it is still very much a unknown. Life is just the mechanism in which DNA replication most successfully occurs, for any given environment of harvestable energy. Is that really up for debate? ---
**Author:** ![Todderbob](https://avatars.discourse-cdn.com/v4/letter/t/e47774/32.png) [@Todderbob](https://boards.straightdope.com/u/Todderbob)\ **Post date:** [January 26, 2009, 8:25pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/52 "2009-01-26T20:25:25Z")
> [@kanicbird](#): > > OK, staying only in the physical realm, so to speak, we really do not know what life really is. People in multi disciplines throughout history have tried to define what life is, **none satisfactory** , though I have no doubt that many feel science will one day discover what life really is, **it is still very much a unknown**. Do you have proof for this claim? > [@kanicbird](#): > > So we are left with putting traits to help define life characteristics we observe, one such trait we notice is DNA, but that does not answer the question about life, just answers a question along the lines ‘does things that have DNA always contain DNA’ I do not understand? ---
**Author:** ![Indistinguishable](https://avatars.discourse-cdn.com/v4/letter/i/90ced4/32.png) [@Indistinguishable](https://boards.straightdope.com/u/Indistinguishable)\ **Post date:** [January 26, 2009, 8:36pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/53 "2009-01-26T20:36:46Z")
> [@The\_Tao\_s\_Revenge](#): > > Somewhere in in the binary version of PI is the code for every computer program that will ever exist, every movie, every book, and song, plus books, songs, stories, and movies of such beauty they’d move armies to lay down their weapons and nations to tears of joy. But they will never be made because no one will ever think of them. And we will never know them. Like everyone says, it’s generally believed but not actually proven that this is true of the binary expansion of π. But no matter… it’s easy to come up with a sequence it _is_ provable of: 0 1 00 01 10 11 000 001 010 011 100 101 110 111 0000 0001 … The fascination with casting these things in terms of π is beyond me. (Hell, as far as I’m concerned, π itself is not the important constant; it’s 2π that’s the special one (not that it changes much as far as this matter goes)) ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [January 26, 2009, 8:37pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/54 "2009-01-26T20:37:27Z")
> [@kanicbird](#): > > OK, staying only in the physical realm, so to speak, we really do not know what life really is. People in multi disciplines throughout history have tried to define what life is, none satisfactory, though I have no doubt that many feel science will one day discover what life really is, it is still very much a unknown. > > So we are left with putting traits to help define life characteristics we observe, one such trait we notice is DNA, but that does not answer the question about life, just answers a question along the lines ‘does things that have DNA always contain DNA’ [Moderating] You are saying here that in your opinion the question in the OP is not answerable. Therefore I think there is really no point in your continuing to post on in this thread. If you want to discuss philosophical or religious aspects of life, please take it to GD. By the same token, I request that other posters not attempt to engage **kanicbird** in debate on this issue here, or else this thread will be even farther derailed. Colibri General Questions Moderator ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 26, 2009, 8:58pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/55 "2009-01-26T20:58:30Z")
Quoth **Colibri** : > [@](#): > > On the other hand, DNA-based life doesn’t have to use exactly the same nucleotides that it does on Earth, and the details of the genetic code would certainly be different. I would consider a molecule which used a different set of nucleotides to be similar to DNA, but not DNA. Certainly the ladder structure is a very convenient one for what DNA does, and I would not be at all surprised to find it used in the significant majority of non-terrestrial life, but there are plenty of different ways you could make the rungs. Quoth **Q. E. D.** : > [@](#): > > It is low in information density. Assuming, as a previous poster noted, the digits of pi follow a normal probability distribution, any arbitrary-length string of digits you care to name will be found. Eventually. Now, it may (to make up some numbers) take a nmber of digits equal to the the number or electrons in the Universe raised to its own power before you find even one complete poem, fore example, and that many raised to it’s own power raised to its own power digits more before you find another. But infinite is really, really big. Assuming that pi is in fact normal, the number of digits you’d have to search before you found your search string would itself take up about as many bits as your search string itself. That is to say, if your search string is 100 bits long, then it would take approximately 2[sup]100[/sup] digits of binary pi before you found your string. Or to put it yet another way, stating the position in pi where you found your copy of War and Peace would take up, on average, exactly as much space as the original War and Peace, but it’d be really difficult to decode. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [January 26, 2009, 9:14pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/56 "2009-01-26T21:14:46Z")
> [@Chronos](#): > > Quoth **Colibri** :I would consider a molecule which used a different set of nucleotides to be similar to DNA, but not DNA. Certainly the ladder structure is a very convenient one for what DNA does, and I would not be at all surprised to find it used in the significant majority of non-terrestrial life, but there are plenty of different ways you could make the rungs. I am talking about something that meets the chemical definition of deoxyribonucleic acid, that is with a 2-deoxyribose backbone combined with nucleobase units. [From here](http://en.wikipedia.org/wiki/Nucleobase), it is possible to incorporate other nucleobases than the standard cytosine, adenine, guanine, and thymine, and these are chemically just as much DNA as the standard form: > [@](#): > > A vast number of nucleobases analogues exist. The most common application are used as fluorescent probes, either directly or indirectly, such as Aminoallyl nucleotide which are used to label cRNA or cDNA in microarrays. Several groups are working on alternative “extra” base pairs to extend the genetic code, such as isoguanine and isocytosine or the fluorescent 2-amino-6-(2-thienyl)purine and pyrrole-2-carbaldehyde. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 26, 2009, 11:17pm UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/57 "2009-01-26T23:17:23Z")
> [@](#): > > I am talking about something that meets the chemical definition of deoxyribonucleic acid, that is with a 2-deoxyribose backbone combined with nucleobase units. OK, I was not aware that the standard definition was independent of the nucleobases used. I still wouldn’t be surprised to see other backbones, though. And at the very least, I would expect that the mirror isomer would be just as common as the one we’re familiar with: Would that also be considered the same substance? ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [January 27, 2009, 2:34am UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/58 "2009-01-27T02:34:02Z")
> [@Chronos](#): > > OK, I was not aware that the standard definition was independent of the nucleobases used. I still wouldn’t be surprised to see other backbones, though. And at the very least, I would expect that the mirror isomer would be just as common as the one we’re familiar with: Would that also be considered the same substance? If it had other backbones (made of something other than deoxyribose), like RNA, then it technically wouldn’t be DNA. I would consider isomers to be the same substance. Of course, the whole system would probably have to be reversed to work, with levo sugars and dextro amino acids. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [January 27, 2009, 4:09am UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/59 "2009-01-27T04:09:14Z")
> [@Kobal2](#): > > Back when I was in med school first year, “life” was determined by 4 criterions : > > 1. Can move on its own > 2. Can reproduce itself > 3. Produces its own energy > 4. I don’t remember the 4th :(. I think it was about having at least one cellular nucleus, but I wouldn’t bet my life on the recollection. Although admittedly, that point would constitute a fairly geocentric definition of life, and constitute a circular answer to the OP. So we may ditch that one. > > But virii don’t move, nor create or consume energy, nor reproduce on their own (they parasite cells and take advantage of \*their \*reproduction mechanisms to create more virii), hence they’re not living creatures by this acception. Neither are red blood cells (to answer another poster). Mithocondriae would be a more complicated matter, though. The necessary (but not generally considered sufficient) conditions for life are:[ol][li]Consumes (or rather, transforms) some form of energy[_]Produces some type of waste (energy in more entropic form)[_]Reproduces itself ‘independently’ of external mechanisms[/ol]. A fourth possible criterion is cellular structure, which we find in anything that would be considered terrestrial life, and for structural and functional reasons we would expect would apply to any form of life, regardless of whether it is based on DNA (or any other organic molecule) or not. [/li] Some may argue that viruses are a primitive form of life, but that misses two important points; first, no virus is capable of self-replication without using the machinery of other organisms, and second, that viruses, far from being simple, are often remarkably complex and highly efficient machines. Their nucleotide sequences may be brief but they are nearly all functional, which is remarkable compared to the (apparent) clutter that is the DNA of most organisms. However, their sparse instruction set is insufficient to provide the functionality needed for reproduction or many other functions that would normally be considered necessary for life. Viruses may therefore be analogized to applets, waiting for a web server to animate, rather than a complete application itself. Prions are even less questionable; as malformed proteins that catalyze other proteins, they are absolutely dependent not only on the mechanisms of other organisms for reproductions, but they also have to be introduced to a field of like proteins in order to work their way. Although prions are an interesting example of error propagation in biochemistry, they can in no way be considered alive or evolutionarily successful by any accepted measure. Every terrestrial organism that we would consider alive has DNA. Whether an organism of extraterrestrial organism (or an unlikely one of terrestrial organism that is able to successfully compete with established DNA-based life) exists is an interesting question. In addition to the possibility of using other sugars for nucleotide bases, there is the possibility of non-carbon bases, and even other structural molecules to form the backbone. However, there are good reasons to believe that the helical structures of RNA and DNA (or something very similar) provide at least ‘an’ and perhaps ‘the’ optimal biological structures for encoding genetic information for ‘complex’ organisms. However, empirically we have only a data set of one, and there could very well be a method we simply haven’t developed because it is too foreign to our existing understanding of chemical structures. > [@elucidator](#): > > If its true that DNA is the basis for alien life forms, then we can eat them! Downside, of course, is that they can eat us. Not likely; while we can probably extract suitable (and perhaps unsuitable) minerals from them, and they might produce the simple sugars in a form that would be accessible to terrestrial gastric systems, their proteins and complex carbohydrates (as well as micronutrients, complex lipid structures, et cetera) would probably be too foreign to digest effectively if at all, and could very possibly be toxic. Stranger ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [January 27, 2009, 4:25am UTC](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849/60 "2009-01-27T04:25:30Z")
> [@Stranger\_On\_A\_Train](#): > > A fourth possible criterion is cellular structure, which we find in anything that would be considered terrestrial life, and for structural and functional reasons we would expect would apply to any form of life, regardless of whether it is based on DNA (or any other organic molecule) or not. There are a few exceptions to that one, such as the [plasmodial or acellular slime molds](http://www.ucmp.berkeley.edu/protista/slimemolds.html) and the algae [Caulerpa](http://www.ucmp.berkeley.edu/protista/slimemolds.html) and [Halimeda](http://reefkeeping.com/issues/2004-04/nftt/index.php). They are coencytic; that is, the organism lacks internal cellular structure, being essentially an enormous single cell with many nuclei. [Previous page](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849.md?page=2) [Next page](https://boards.straightdope.com/t/is-it-legitimate-to-say-that-all-living-things-have-dna/482849.md?page=4)