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#1
Old 01-24-2009, 06:47 PM
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Is it legitimate to say that all living things have DNA?

Or, are there any organisms that fit the basic concept of "living" which don't have DNA? If so, what do they have, and how do they qualify as living?

Last edited by Zyada; 01-24-2009 at 06:48 PM. Reason: Punctuation is a good thing
#2
Old 01-24-2009, 06:57 PM
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Some viruses contain RNA and not DNA. See http://en.wikipedia.org/wiki/Virus_classification

Whether you want to count a virus as a "living thing" is basically a semantic choice.
#3
Old 01-24-2009, 08:21 PM
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There are also self-replicating ribozymes, made entirely of RNA, and prions, which are apparently pure protein, though they may require a scaffold of RNA or other polyanions to fold properly - the jury's still out on that. Both of those are pushing the definition of "life" quite a bit, though.
#4
Old 01-24-2009, 08:31 PM
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Are red blood cells alive?
#5
Old 01-24-2009, 08:55 PM
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From the field of astronomy we understand that the rate of the universe's expansion is such that it must already be infinite in size. Earth has life, so the probability of a star having a planet circling it with life is greater than zero. Therefore, with an infinite number of stars in the universe, there must be an infinite number of planets with life, too.

While it seems hard to say with confidence, I think it is most reasonable to suppose that not all of these life forms on these planets use DNA, and there would be an infinite number of kinds of life that don't use DNA..
#6
Old 01-24-2009, 11:30 PM
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Originally Posted by Napier View Post
From the field of astronomy we understand that the rate of the universe's expansion is such that it must already be infinite in size
Do we know this for sure?
#7
Old 01-24-2009, 11:33 PM
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Originally Posted by Shamozzle View Post
Do we know this for sure?
No.
#8
Old 01-24-2009, 11:38 PM
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But to further Napier's point, is how fascinating it would be to discover life elsewhere in the universe that doesn't use the DNA/Double-Helix mechanism for encoding genes and producing organisms.

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.
#9
Old 01-25-2009, 12:01 AM
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Quote:
Originally Posted by Napier View Post
From the field of astronomy we understand that the rate of the universe's expansion is such that it must already be infinite in size. Earth has life, so the probability of a star having a planet circling it with life is greater than zero. Therefore, with an infinite number of stars in the universe, there must be an infinite number of planets with life, too.
Even if the Universe is infinite in size, there still a finite amount of matter in the universe.

It's not infinite, it's just a really, really big finite number.
#10
Old 01-25-2009, 12:12 AM
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Originally Posted by cmyk View Post
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.
Personally, I'd be surprised. I'm sure there could be other systems that would work equally well.
#11
Old 01-25-2009, 12:20 AM
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I'm sure our sexy alien overlords will have TNA.
#12
Old 01-25-2009, 12:31 AM
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Originally Posted by bibliophage View Post
Some viruses contain RNA and not DNA. See http://en.wikipedia.org/wiki/Virus_classification

Whether you want to count a virus as a "living thing" is basically a semantic choice.
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.
#13
Old 01-25-2009, 09:18 AM
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I propose evolution is a good definition of life. If it has descendants that adapt to their environment over time then it's alive.
#14
Old 01-25-2009, 09:34 AM
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Originally Posted by Squink View Post
Are red blood cells alive?
It depends on your definition. They don't reproduce and they're part of a larger organism.
#15
Old 01-25-2009, 10:45 AM
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>Do we know this for sure?

As I understand it, the answer is yes, sort of. More precisely, in the current understanding of cosmology, the details that would weigh in on this question have all been confidently decided and the answer is, yes, measurements confirm, the universe is infinite. I think it is prudent, though, to note how widely theories have ranged in recent decades on this question, and to say that it is hard to confidently predict that we will not change our minds on this in the next few decades. So, if I had to decide now, I would accept the universe as infinite and the number of planets with life forms as also infinite.

>Even if the Universe is infinite in size, there still a finite amount of matter in the universe.

Todderbob, I've never heard such a statement and on the basis of what I have heard understand it to be incorrect. Why do you say this?
#16
Old 01-25-2009, 10:53 AM
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Originally Posted by Napier View Post
>Do we know this for sure?

As I understand it, the answer is yes, sort of. More precisely, in the current understanding of cosmology, the details that would weigh in on this question have all been confidently decided and the answer is, yes, measurements confirm, the universe is infinite. I think it is prudent, though, to note how widely theories have ranged in recent decades on this question, and to say that it is hard to confidently predict that we will not change our minds on this in the next few decades. So, if I had to decide now, I would accept the universe as infinite and the number of planets with life forms as also infinite.
You can't measure infinity. We can only say that we haven't found any boundaries yet.
#17
Old 01-25-2009, 11:29 AM
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Infinity is not measured. It is determined. More specifically, no finite universe can become infinite so the presumption must be made that the universe was infinite at its creation (assuming it has one rather than being eternal). That means that the theoretical assumptions for how the universe was created determines whether it is infinite in extent or not.

Since there is no consensus on how the universe was created, its status as infinite or finite is dependent on the individual model used.

Whichever model is used, for all practical purposes no information can ever reach us about areas of the universe that are past light speed communication with earth, now or in the past. Even with expansion that puts an absolute limit of about 67 billion light years as the boundaries of our universe.

You can make theoretical speculation about what lies beyond that, just as you can speculate about multiverses with different physical laws than ours. But that has as much meaning today as speculating about the infinite number of shades of pink in the Invisible Pink Unicorn.

We've done this in a million other threads. How about not hijacking this one?
#18
Old 01-25-2009, 12:30 PM
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Originally Posted by Napier View Post
Todderbob, I've never heard such a statement and on the basis of what I have heard understand it to be incorrect. Why do you say this?
Because matter is neither created nor destroyed.

If matter is neither created nor destroyed, only converted. If there's X matter in the universe today, there will be X matter in the universe tomorrow. No more, no less.

That's still a finite number.

While the amount of space may increase exponentially, the matter will always be the same. If it's always the same, it has a finite number. It may be an immessurably large finite number, but it is a finite number.
#19
Old 01-25-2009, 12:36 PM
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Originally Posted by Napier View Post
From the field of astronomy we understand that the rate of the universe's expansion is such that it must already be infinite in size. Earth has life, so the probability of a star having a planet circling it with life is greater than zero. Therefore, with an infinite number of stars in the universe, there must be an infinite number of planets with life, too.

While it seems hard to say with confidence, I think it is most reasonable to suppose that not all of these life forms on these planets use DNA, and there would be an infinite number of kinds of life that don't use DNA..
If this is true, then there are an infinite number of creatures named "Napier" out there; and an infinite number of them posting on message boards; and so on; so that there is an infinite number of people out who are arbitrarily similar to you, down to the thoughts going through your head.

No?
#20
Old 01-25-2009, 02:24 PM
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Originally Posted by Napier View Post
From the field of astronomy we understand that the rate of the universe's expansion is such that it must already be infinite in size. Earth has life, so the probability of a star having a planet circling it with life is greater than zero. Therefore, with an infinite number of stars in the universe, there must be an infinite number of planets with life, too.
From the field of mathematics, we know that there are an infinite number of natural numbers. The number two is an even prime, so the probability of a number being an even prime is greater than zero. Therefore, with an infinite number of natural numbers, there must be an infinite number of even primes.

(Which is to say: one needs to be careful when making probability arguments with infinite sets.)
#21
Old 01-25-2009, 02:48 PM
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To sum up the cosmology arguments: The simplest models of the Universe consistent with our best current data say that the Universe is infinite, but there are also models which are only slightly more complex that say that it's finite, so we can't really say one way or the other. If it's infinite in size, then it contains an infinite amount of matter, and it has always been infinite in size and contained an infinite amount of matter. In any event, it's sufficiently huge that even the most pessimistic estimates of the Drake factors indicate that there is almost certainly other life out there, albeit possibly at an inconveniently large distance from us. 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.
#22
Old 01-25-2009, 02:58 PM
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Several of these posts about cosmology seem to require answers, and yet I don't mean to hijack a thread about DNA.

Chronos's summary seems reasonable and is consistent with what I remember reading and studying. More to the point, it supports the view that "there is almost certainly other life out there", which I think is hard to doubt, and which is very relevant to the OP. This seems an excellent time to accept that conclusion for what it is worth in light of the OP. Thanks, Chronos.
#23
Old 01-25-2009, 03:02 PM
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My own view is that life in physical form uses cellular structures that have DNA, but are spiritual beings and that being continues past the death of the physical body, other such beings such as angels do not contain physical matter but are very much alive.
#24
Old 01-25-2009, 05:41 PM
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Could you say

"All living things have DNA, but not all things with DNA are alive?"
#25
Old 01-25-2009, 08:44 PM
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Originally Posted by MikeS View Post
From the field of mathematics, we know that there are an infinite number of natural numbers. The number two is an even prime, so the probability of a number being an even prime is greater than zero. Therefore, with an infinite number of natural numbers, there must be an infinite number of even primes.

(Which is to say: one needs to be careful when making probability arguments with infinite sets.)
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.

Last edited by The Tao's Revenge; 01-25-2009 at 08:46 PM.
#26
Old 01-25-2009, 08:49 PM
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Originally Posted by Chronos View Post
If it's infinite in size, then it contains an infinite amount of matter, and it has always been infinite in size and contained an infinite amount of matter.
Not necessarily.

Something can be infinitely large, but not be full.
#27
Old 01-25-2009, 08:57 PM
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I tried to edit in the following, but missed my deadline.

ETA: There are 4 possibilities. (I won't go into the specifics of each theory, just the overall basics of what they are.)

A1. A2. B1. B2.

A) The universe is of infinite size.

B) The universe is of finite size.

1) The universe contains an infinite amount of matter.

2) The universe contains a finite amount of matter.


A1: This is internally consistent, though difficult for me to believe, mathematically speaking.

A2: This is internally consistent as well, and would lead to a 'big rip,' eventually. Because we do know that the universe is -- or has so far been --expanding (See: The Metric Expansion of Space).

B1: This is internally inconsistent and difficult for me to believe, because for an infinite amount of material of material to reside in a finite space, it would have to be infinitely dense... and... that's just not how the universe seems to me.

B2. This is the theory I lean towards, because it's internally consistent and it seems to account, best, for what we observe in the universe. The universe has a finite, if undefined, size, and a finite, if undefined amount of matter.
#28
Old 01-25-2009, 09:00 PM
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Originally Posted by kanicbird View Post
My own view is that life in physical form uses cellular structures that have DNA, but are spiritual beings and that being continues past the death of the physical body, other such beings such as angels do not contain physical matter but are very much alive.
[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.

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#29
Old 01-25-2009, 09:01 PM
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Originally Posted by kanicbird View Post
My own view is that life in physical form uses cellular structures that have DNA, but are spiritual beings and that being continues past the death of the physical body, other such beings such as angels do not contain physical matter but are very much alive.
This is GQ. Unless you can point to an angel or other spiritual being, preferably one on display under glass at a major museum, keep your unverifiable personal beliefs out of the discussion.
#30
Old 01-25-2009, 09:02 PM
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Originally Posted by Exapno Mapcase View Post
This is GQ. Unless you can point to an angel or other spiritual being, preferably one on display under glass at a major museum, keep your unverifiable personal beliefs out of the discussion.
[Moderator Note]

I realized you simulposted, but please leave the moderating of this forum to the moderators. Thanks.

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#31
Old 01-25-2009, 09:26 PM
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Quote:
A1: This is internally consistent, though difficult for me to believe, mathematically speaking.

A2: This is internally consistent as well, and would lead to a 'big rip,' eventually. Because we do know that the universe is -- or has so far been --expanding (See: The Metric Expansion of Space).
The thing is, the density of the Universe seems to be more or less uniform. If the Universe is infinite in size but contains a finite amount of matter, then the average density must be zero, and we living in a region where it's not would have to be a very special region of the Universe indeed. The assumption that we occupy a special place in the Universe has had a very bad history, and it seems to go against everything that we can observe now.

And such a universe would not, incidentally, undergo a Big Rip. It (like our apparently uniform-density Universe) would expand forever at an ever-increasing rate, but the expansion would be exponential, with a fixed doubling time. A Big Rip depends not on any of the properties of the normal matter in the Universe, but on the dark energy: In a Big Rip model, the dark energy gets stronger with time, such that the doubling time of the size of the universe gets shorter and shorter without limit. In a normal Cosmological Constant universe (as ours appears to probably be), the expansion of space is never significant on the scale of people, planets, or even galactic clusters, while in a Big Rip universe, eventually even atoms and subatomic particles are torn apart by the expansion.

This is getting rather far afield of the OP, though. If you want to discuss it further, perhaps you could start a new thread.
#32
Old 01-25-2009, 10:05 PM
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This is getting rather far afield of the OP, though. If you want to discuss it further, perhaps you could start a new thread.
I would think that would be a good idea. I don't want to cut off the discussion, but it isn't directly related to the OP. A new thread linked to this one for those who are interested in pursuing this discussion would be the best option.

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#33
Old 01-25-2009, 10:06 PM
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I would think that would be a good idea. I don't want to cut off the discussion, but it isn't directly related to the OP. A new thread linked to this one for those who are interested in pursuing this discussion would be the best option.

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I put one up, here.
#34
Old 01-25-2009, 10:18 PM
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Originally Posted by Kobal2 View Post
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.
I'm sure you are misrembering the criteria. Obviously #1 is wrong, since plants and other sessile organisms don't move. You are probably thinking of "respond to stimuli." Likewise "produces its own energy" should be "consumes and uses energy" since organisms don't produce their own energy. Having a cellular nucleus is also wrong, since bacteria lack one.

Quote:
But virii don't move,
The only real plural of virus in English is viruses; the original Latin term did not have a plural.

Just out of curiosity, did you ever graduate from Med School?
#35
Old 01-25-2009, 11:00 PM
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When I was back there in medical school
There was a person there
Who put forth the proposition
That "life" was determined by 4 criterions
"life" was determined by 4 criterions
"life" was determined by 4 criterions
Life is not determined by these four criterions!

...

When all else fails
We can whip Ed Zotti's eyes
And make him leap
And scry.
#36
Old 01-26-2009, 04:44 AM
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Originally Posted by brazil84 View Post
If this is true, then there are an infinite number of creatures named "Napier" out there; and an infinite number of them posting on message boards; and so on; so that there is an infinite number of people out who are arbitrarily similar to you, down to the thoughts going through your head.

No?
Your post reminded me of this article from the old Brunching Shuttlecocks site:

Monkeys, Numbers, and You

#37
Old 01-26-2009, 07:25 AM
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Originally Posted by The Tao's Revenge View Post
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.
The part about Pi is incredibly wrong. Pi is not in any way high information content. It is quite low which is why there are such simple algorithms to compute it. What you state is completely against well known theorems in computability and complexity theory.
#38
Old 01-26-2009, 07:52 AM
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Originally Posted by Colibri View Post
I'm sure you are misrembering the criteria. Obviously #1 is wrong, since plants and other sessile organisms don't move. You are probably thinking of "respond to stimuli."
Good point.

Quote:
Just out of curiosity, did you ever graduate from Med School?
Good lord, no. I didn't even finish the first year - the competitive nastiness of students was waYYY over my threshold. I'm a lazy bum, too, so there's that
#39
Old 01-26-2009, 07:56 AM
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Originally Posted by ftg View Post
Pi is not in any way high information content
Yes, but it's very long.

http://pi.nersc.gov/
Code:
Pi-Search Result:


search string = "obama"
25-bit binary equivalent = 0111100010000010110100001

search string found at binary index = 2302530316
binary pi : 0111001001111000100000101101000010000000111010101100001110101011
binary string: 0111100010000010110100001 
character pi : .agshvn,alspqsrobama_gjxnuuf.utjpv,u,w
character string: obama
The first first four billion binary digits of Pi contain every five letter word.
#40
Old 01-26-2009, 08:44 AM
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Originally Posted by ftg View Post
The part about Pi is incredibly wrong. Pi is not in any way high information content. It is quite low which is why there are such simple algorithms to compute it. What you state is completely against well known theorems in computability and complexity theory.
It is conjectured (though not yet proven) that pi is a normal number. If true, then any digital string you'd care to name, of any length, is encoded in it. This doesn't mean, of course, that calculating the digits of pi is the best way to get a copy of Raphael's Portrait of a Young Man or a DVD of Spinal Tap 2: Derek's Revenge; merely that in principle, it could be done.
#41
Old 01-26-2009, 09:35 AM
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Originally Posted by cmyk View Post
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.)
#42
Old 01-26-2009, 09:48 AM
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Originally Posted by Chronos View Post
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.
#43
Old 01-26-2009, 10:02 AM
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Originally Posted by ftg View Post
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.

Last edited by Q.E.D.; 01-26-2009 at 10:02 AM.
#44
Old 01-26-2009, 11:25 AM
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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.
#45
Old 01-26-2009, 11:30 AM
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Originally Posted by sweepkick View Post
Your post reminded me of this article from the old Brunching Shuttlecocks site:

Monkeys, Numbers, and You

Thank you. You might enjoy a short story called "The Library of Babel" written by Borges.
#46
Old 01-26-2009, 12:03 PM
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Originally Posted by Colibri View Post
[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.

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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'
#47
Old 01-26-2009, 12:08 PM
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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.

Last edited by brujaja; 01-26-2009 at 12:09 PM. Reason: Crystalline intelligence?
#48
Old 01-26-2009, 12:30 PM
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Originally Posted by elucidator View Post
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.
#49
Old 01-26-2009, 01:55 PM
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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.
#50
Old 01-26-2009, 02:18 PM
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Quote:
Originally Posted by Smeghead View Post
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'.
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