Recently in a mailing list I belong to, a friend proposed the following puzzle, which I will reproduce in its entirety (minus the friend's identifying details). I answered him at enough length that I wanted to preserve the discussion.
I will start with the disclaimer that I am not a biologist, let alone an evolutionary biologist, let more alone an evolutionary biologist specializing on origin-of-life studies, so this is all from recent research (and I'll get into the philosophy of science a bit as well).
You asked a cascade of interesting questions about the origin of life. It in indeed a puzzle and one of the most complicated and interesting puzzles we have about the natural world. Life is complicated, and at first blush it's obvious that some things are alive and some things are not. I will continue to harp on this fact: in biology, the boundaries are fuzzy--almost all of them. Sofia Vergara is alive (gloriously alive), and a rock is not alive. That's clear. But just because we can usefully and correctly categorize these two things into these two categories doesn't mean there isn't a fuzzy boundary. When you look very closely at that boundary, as you do with premise #1, you have to start qualifying things. Sofia Vergara and rocks are both collections of atoms that form a sort-of unit with a boundary (again, a fuzzy boundary, but a boundary). As such they are on a continuum. You say it well:
So that's perfectly fair. RNA snippets are often excluded when talking about what is alive and what is not alive. Yeasts are often excluded from the life discussion as well.
But that doesn't mean that in reality they are not on the continuum. By most definitions an RNA snippet is not alive, and that makes some conversation and study into life much easier, because you can talk about "all life is made up of cells". But saying that an RNA snippet is not life is just that, a statement that makes the study of most of life much easier. But reality stubbornly continues to be reality. We call things "alive" or "not alive" but those definitions are our invention. At the boundaries it is nearly impossible to distinguish between the simplest alive thing and the most complicated not-alive thing.
We often talk about species the same way. Sofia Vergara (look her up, she is really super-alive--in this case research can be fun!) is a human (Homo Sapiens). A broccoli plant (less fun to research than Jessica Alba, but sacrifices must be made) is a different species (Brassica Oleracea). That they are different species is true, in the sense that we invented the term "species" exactly so we could have conversations about divisions of life. Again, at the borders it is fuzzy. Cauliflower, for instance, is also Brassica Oleracea. Cauliflower is mostly a different species than broccoli, or at least it is kind of a different species, or it's useful in some contexts to call them different species, and in some others it's more useful to call them the same species. At the boundaries it's fuzzy.
This is true not just of plants, but also of complicated higher animals. I haven't looked it up recently but I think it's true that there are enough dolphin species on Earth that there are lots of what we call dolphin species that have really fuzzy boundaries.
So I'm all behind disqualifying RNA snippets as life for the purposes of this discussion, but it's a false dichotomy to say that there is "life" and "not life" as perfectly disjoint sets.
No question. "Incredible" hardly does it justice.
I agree in the sense that Shakespeare's written plays also "do nothing" on their own. If all humans died tomorrow and the Earth and all its artifacts remained undiscovered by any alien intelligence until the heat death of the universe, a book of those plays would be indistinguishable from any other collection of matter. This whole premise #3 presupposes that "function" has some objective meaning. This is not sophistry, I mean it as a serious part of this discussion. What is a rock "for"? Out in space by itself or rolling down a mountain side--which condition fulfills the rock's purpose? Shakespeare's plays have meaning because we all (as intelligent agents) agree on some common definition of their purpose.
I think you mean that DNA cannot go about the business of being life on its own. Again, for the purposes of this discussion I agree that it makes sense to say that DNA does nothing.
I think I object the word "special" to describe the form of DNA, but it is certainly a particular shape and structure. I only make this point because I think "special" kind of pre-answers the whole puzzle... it reveals what your answer to the puzzle is. Unsurprising to you, I'm sure, is that I think I'm going to answer this puzzle differently than you will, ultimately.
Like the Shakespeare's Plays example I used above "use the DNA for something" presupposes that it has an objective use. The plays (in a book form) could be used to fly through space and re-enter an alien planet to be observed by some aliens looking for shooting stars. Does that book of plays have a purpose beyond its physical interaction with other matter in the universe? Only because a collection of humans agree that it does. I agree, however, that DNA's business of acting as a blueprint for copying units of life cannot be carried on without a bunch of other pieces in place.
True, this process, in order to continue and do the thing that we think of as its purpose, needs to be proximate and protected.
I disagree with this as a premise, and I think most biologists would, too. Here's an example:
We can create machines that make copies of themselves, much like life at the cellular level recapitulates itself. But in order to kick the whole thing off, there is not infinite regress, something else assembles the first machine. I suspect that this statement argues for some other point you imply, but it ultimately argues for both of us.
I don't know.
I'll want to say that the cell wall, while interesting and amazing, does not belong in this discussion. It's very valuable, but it's not impossible for life to proceed without it... higher-lever, organized living creatures need them (Sofia Vergara, for instance, would be far less compelling without the her cell walls), but there's no reason to think that life in its basic form can't get along without cell walls, it needs protection and some proximity, but not necessarily cell walls.
As to the rest of the mechanisms, there are theories. None of them are definitive... like a lot of the very basic science, we will probably never know the answer to a perfect level of confidence. One thing that science is is provisional. Every understanding we have about the natural world (that science has about the natural world) is provisional to some other contradictory evidence disproving our theories.
That having been said, some things are more well known than others, and certain facts about the universe are simply more amenable to answering than others.
Some point of discussion:
The laws of planetary motion are really well understood. They were not initially. There was also a time when the question about how the planets moved may have seemed unanswerable, we lacked the knowledge of what they were, how the solar system was physically arranged, how gravity worked and we even lacked the mathematics to describe it. Slowly and with effort and a lot of years (centuries, in fact) we slowly brought our understanding into focus and it turns out that planetary motion is pretty amenable to understanding. We do not believe that we completely understand planetary motion, it is not 100% sure, but it is, say, 99.999% sure that we do.
How life began is exactly as factual as how planets move. In other words there is an answer to the question. On a theoretical basis it is 100% knowable. It is a harder problem than planetary motion to get at the facts that could answer the question. As a practical matter our assurance that we know the answer of how life began will always have a lower percentage of assurance than for planetary motion.
In a general sense, science is all about developing better and better theories about the natural world. These are often called "models". Our model of planetary motion is really good (we don't know of anything right now that proves our model is not 100%, but science is always provisional). Our model of the large structure of the universe is less good. It's still pretty good, really good in fact, but there are outstanding facts we know about the universe that don't fit the model (dark energy and dark matter are two issues that prove our model is not 100% accurate).
So where do current theories of origin-of-life sit in terms of this "model assurance" discussion? Well pretty far below the others I've discussed.
But that doesn't mean the answers are unknowable. Just that they unknown today. Anything unknown today might remain unknown forever. The origin of things before our direct observation are always more hampered at getting to that 100% model assurance than things we can test more readily.
I suspect that your question is meant to lead the reader toward the conclusion that because we can't answer the final question that the theory of evolution is therefore untenable. I'll address that point directly:
First, we actually agreed more than we disagreed on your premises.
Second, how life began is a fundamentally different question than whether or not evolution is happening, and whether or not evolution drives speciation. (the diversity of species of life)
Third, not knowing how something is happening, or how it began, is not the same as knowing that it happens. Evolution is happening, more and more we understand the mechanism for it, but it is happening.
Fourth, the fuzziness of the boundaries of definition is the key to understanding that evolution drives speciation. Broccoli and Cauliflower are different species... kind of and almost and almost-not and all of that. They are certainly on a continuum that includes broccoli, cauliflower, mustard plants, oak trees, and even animals and humans. Because it's hard to find the boundaries at the most granular level doesn't mean it's not meaningful to talk about the difference between species; conversely, talking about the (working) definitions of species doesn't imply that these things don't lie on a continuum.
Cheers!
[As a point of reference, my discussion of the false dichotomy and continuum of speciation owes a great deal to Dr. Stephen Novella who, to my knowledge, first phrased in the way I've presented it.]
Here's a puzzle I have yet to get valid answer for.
The suppositions first...
1) All life requires DNA. (RNA viral snippets we will not considered to be alive as they have to corrupt a functioning cell to reproduce themselves. For this puzzle they are moot)
2) DNA is an incredible information strand that outlines how proteins are to be built.
3) DNA can do nothing on its own, as its just information encoded.
4) DNA requires a relatively complex decoding sequence to unravel it (it's in a special compressed double helix form), read it, and then build the proteins it describes. I.E. quite a number of intricate molecular machines need to be running to access the DNA and do this work to use the DNA for something.
5) This unraveling, reading and building needs to take place where its not interrupted or spread out. I.e. in a shell of some sort like a cell wall.
6) The original life form which all life is hypothesized to evolved from, had to have DNA, the complex decoder and a shell to keep it all together. Or the unraveled, decoder, and builder parts etc would all drift apart.
Now the puzzle.
If things evolved as hypothesized, where did the first DNA come from? More importantly where did the cell wall, the first decoder that reads DNA and the molecular machinery to act on what is says come from also?
I will start with the disclaimer that I am not a biologist, let alone an evolutionary biologist, let more alone an evolutionary biologist specializing on origin-of-life studies, so this is all from recent research (and I'll get into the philosophy of science a bit as well).
You asked a cascade of interesting questions about the origin of life. It in indeed a puzzle and one of the most complicated and interesting puzzles we have about the natural world. Life is complicated, and at first blush it's obvious that some things are alive and some things are not. I will continue to harp on this fact: in biology, the boundaries are fuzzy--almost all of them. Sofia Vergara is alive (gloriously alive), and a rock is not alive. That's clear. But just because we can usefully and correctly categorize these two things into these two categories doesn't mean there isn't a fuzzy boundary. When you look very closely at that boundary, as you do with premise #1, you have to start qualifying things. Sofia Vergara and rocks are both collections of atoms that form a sort-of unit with a boundary (again, a fuzzy boundary, but a boundary). As such they are on a continuum. You say it well:
1) All life requires DNA. (RNA viral snippets we will not considered to be alive as they have to corrupt a functioning cell to reproduce themselves. For this puzzle they are moot)
So that's perfectly fair. RNA snippets are often excluded when talking about what is alive and what is not alive. Yeasts are often excluded from the life discussion as well.
But that doesn't mean that in reality they are not on the continuum. By most definitions an RNA snippet is not alive, and that makes some conversation and study into life much easier, because you can talk about "all life is made up of cells". But saying that an RNA snippet is not life is just that, a statement that makes the study of most of life much easier. But reality stubbornly continues to be reality. We call things "alive" or "not alive" but those definitions are our invention. At the boundaries it is nearly impossible to distinguish between the simplest alive thing and the most complicated not-alive thing.
We often talk about species the same way. Sofia Vergara (look her up, she is really super-alive--in this case research can be fun!) is a human (Homo Sapiens). A broccoli plant (less fun to research than Jessica Alba, but sacrifices must be made) is a different species (Brassica Oleracea). That they are different species is true, in the sense that we invented the term "species" exactly so we could have conversations about divisions of life. Again, at the borders it is fuzzy. Cauliflower, for instance, is also Brassica Oleracea. Cauliflower is mostly a different species than broccoli, or at least it is kind of a different species, or it's useful in some contexts to call them different species, and in some others it's more useful to call them the same species. At the boundaries it's fuzzy.
This is true not just of plants, but also of complicated higher animals. I haven't looked it up recently but I think it's true that there are enough dolphin species on Earth that there are lots of what we call dolphin species that have really fuzzy boundaries.
So I'm all behind disqualifying RNA snippets as life for the purposes of this discussion, but it's a false dichotomy to say that there is "life" and "not life" as perfectly disjoint sets.
2) DNA is an incredible information strand that outlines how proteins are to be built.
No question. "Incredible" hardly does it justice.
3) DNA can do nothing on its own, as its just information encoded.
I agree in the sense that Shakespeare's written plays also "do nothing" on their own. If all humans died tomorrow and the Earth and all its artifacts remained undiscovered by any alien intelligence until the heat death of the universe, a book of those plays would be indistinguishable from any other collection of matter. This whole premise #3 presupposes that "function" has some objective meaning. This is not sophistry, I mean it as a serious part of this discussion. What is a rock "for"? Out in space by itself or rolling down a mountain side--which condition fulfills the rock's purpose? Shakespeare's plays have meaning because we all (as intelligent agents) agree on some common definition of their purpose.
I think you mean that DNA cannot go about the business of being life on its own. Again, for the purposes of this discussion I agree that it makes sense to say that DNA does nothing.
4) DNA requires a relatively complex decoding sequence to unravel it (it's in a special compressed double helix form), read it, and then build the proteins it describes. I.E. quite a number of intricate molecular machines need to be running to access the DNA and do this work to use the DNA for something.
I think I object the word "special" to describe the form of DNA, but it is certainly a particular shape and structure. I only make this point because I think "special" kind of pre-answers the whole puzzle... it reveals what your answer to the puzzle is. Unsurprising to you, I'm sure, is that I think I'm going to answer this puzzle differently than you will, ultimately.
Like the Shakespeare's Plays example I used above "use the DNA for something" presupposes that it has an objective use. The plays (in a book form) could be used to fly through space and re-enter an alien planet to be observed by some aliens looking for shooting stars. Does that book of plays have a purpose beyond its physical interaction with other matter in the universe? Only because a collection of humans agree that it does. I agree, however, that DNA's business of acting as a blueprint for copying units of life cannot be carried on without a bunch of other pieces in place.
5) This unraveling, reading and building needs to take place where its not interrupted or spread out. I.e. in a shell of some sort like a cell wall.
True, this process, in order to continue and do the thing that we think of as its purpose, needs to be proximate and protected.
6) The original life form which all life is hypothesized to evolved from, had to have DNA, the complex decoder and a shell to keep it all together. Or the unraveled, decoder, and builder parts etc would all drift apart.
I disagree with this as a premise, and I think most biologists would, too. Here's an example:
We can create machines that make copies of themselves, much like life at the cellular level recapitulates itself. But in order to kick the whole thing off, there is not infinite regress, something else assembles the first machine. I suspect that this statement argues for some other point you imply, but it ultimately argues for both of us.
Now the puzzle.
If things evolved as hypothesized, where did the first DNA come from?
I don't know.
More importantly where did the cell wall, the first decoder that reads DNA and the molecular machinery to act on what is says come from also?
I'll want to say that the cell wall, while interesting and amazing, does not belong in this discussion. It's very valuable, but it's not impossible for life to proceed without it... higher-lever, organized living creatures need them (Sofia Vergara, for instance, would be far less compelling without the her cell walls), but there's no reason to think that life in its basic form can't get along without cell walls, it needs protection and some proximity, but not necessarily cell walls.
As to the rest of the mechanisms, there are theories. None of them are definitive... like a lot of the very basic science, we will probably never know the answer to a perfect level of confidence. One thing that science is is provisional. Every understanding we have about the natural world (that science has about the natural world) is provisional to some other contradictory evidence disproving our theories.
That having been said, some things are more well known than others, and certain facts about the universe are simply more amenable to answering than others.
Some point of discussion:
The laws of planetary motion are really well understood. They were not initially. There was also a time when the question about how the planets moved may have seemed unanswerable, we lacked the knowledge of what they were, how the solar system was physically arranged, how gravity worked and we even lacked the mathematics to describe it. Slowly and with effort and a lot of years (centuries, in fact) we slowly brought our understanding into focus and it turns out that planetary motion is pretty amenable to understanding. We do not believe that we completely understand planetary motion, it is not 100% sure, but it is, say, 99.999% sure that we do.
How life began is exactly as factual as how planets move. In other words there is an answer to the question. On a theoretical basis it is 100% knowable. It is a harder problem than planetary motion to get at the facts that could answer the question. As a practical matter our assurance that we know the answer of how life began will always have a lower percentage of assurance than for planetary motion.
In a general sense, science is all about developing better and better theories about the natural world. These are often called "models". Our model of planetary motion is really good (we don't know of anything right now that proves our model is not 100%, but science is always provisional). Our model of the large structure of the universe is less good. It's still pretty good, really good in fact, but there are outstanding facts we know about the universe that don't fit the model (dark energy and dark matter are two issues that prove our model is not 100% accurate).
So where do current theories of origin-of-life sit in terms of this "model assurance" discussion? Well pretty far below the others I've discussed.
But that doesn't mean the answers are unknowable. Just that they unknown today. Anything unknown today might remain unknown forever. The origin of things before our direct observation are always more hampered at getting to that 100% model assurance than things we can test more readily.
I suspect that your question is meant to lead the reader toward the conclusion that because we can't answer the final question that the theory of evolution is therefore untenable. I'll address that point directly:
First, we actually agreed more than we disagreed on your premises.
Second, how life began is a fundamentally different question than whether or not evolution is happening, and whether or not evolution drives speciation. (the diversity of species of life)
Third, not knowing how something is happening, or how it began, is not the same as knowing that it happens. Evolution is happening, more and more we understand the mechanism for it, but it is happening.
Fourth, the fuzziness of the boundaries of definition is the key to understanding that evolution drives speciation. Broccoli and Cauliflower are different species... kind of and almost and almost-not and all of that. They are certainly on a continuum that includes broccoli, cauliflower, mustard plants, oak trees, and even animals and humans. Because it's hard to find the boundaries at the most granular level doesn't mean it's not meaningful to talk about the difference between species; conversely, talking about the (working) definitions of species doesn't imply that these things don't lie on a continuum.
Cheers!
[As a point of reference, my discussion of the false dichotomy and continuum of speciation owes a great deal to Dr. Stephen Novella who, to my knowledge, first phrased in the way I've presented it.]
2 comments:
The real problem with this puzzle is that there are several inaccuracies and ambiguities in the premises.
1.) the asker attempts to define this question (Where did the first DNA come from?) as a puzzle and then defines certain possibilities as "out of bounds" when in fact this is more properly described as a provable (or at least testable) question about the world as it exists. No possibilities are considered "out of bounds" a priori.
2.) What is "life"? That is not defined, is it? Are viruses alive? They do not metabolize but they do replicate. This is a very salient point since it is quite probable that proto-viruses predated prokaryotic life.
3.) Many viruses, including HIV, have RNA genomes. These are not simple "snippets" but incredibly elegant and robust genomes, less complex than eukaryotes but not much less complex than the simpler prokaryotes.
4.) DNA as it exists now is mostly passive. However, nucleic acids do have self-assembly capacity. This is exhibited in modern calls by tRNA, which assembles amino acids into protein strings. Similar mechanisms allow for *NA assembly. (fun fact: it is hypothesized that proteins predated *NA and served as the initial "scaffolding" for nucleic acid assembly, as *NA now serves as the scaffold for protein assembly. Cute, eh?)
5.) The shell restriction is also spurious. Any concentrated milieu or diffusion-limited environment could have allowed complex molecule processes to occur.
6.) "The original life form which all life is hypothesized to evolved from, had to have DNA" Again a faulty premise. RNA is decidedly the ancestral form and the likelihood is overwhelming that the first living organisms were RNA based.
So where did the first DNA come from? Put simply, it came from an RNA-based mechanism of some variety. It's a chicken-egg shell game -- the egg came first. It was laid by something that wasn't quite a chicken.
The person who posed this question simply didn't know much about biology or biogenesis. The first cell didn't spring into existence de novo, much as the functioning mammalian eye didn't spontaneously appear in one generation. Simple random self-assembly slowly acquired more and more complexity over a great many repetitions, adding a single new step at a time until something that we might recognize as "life" was there. But there was no "first cell" just as there was no "first human."
The real problem with this puzzle is that there are several inaccuracies and ambiguities in the premises.
Of course. I hit on the ones that really struck me, but of course there are a lot of things to talk through.
I think ultimately your points 2 & 5 I hit on directly, but your others are equally valid to my mind. I especially think your point #6 is something I should have jumped on as well: the premise is just an incorrect premise.
The post came from a mailing list I am on, proposed by a person I like and respect. I think the original concept sounds like a William Dembski argument.
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