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A statement I recently read: 'Evolution is debunked and gives no basis for morality. Natural Selection throws away info, it does not add. You need DNA to make RNA, and RNA to make DNA, so they had to come into existence at the same time. Created.'. Who can shed a light?

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    $\begingroup$ Mutual dependence does not imply simultaneous springing into existence. $\endgroup$ – user37894 Oct 24 '18 at 13:38
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    $\begingroup$ I think its rather ironic to note that without question, this same "logic" (stupid as it is) could be used to "disprove" the existence of God, since no creator could exist without being created by the creator... Also, evolution has never been claimed to provide morality. Darwin was so repelled by parasitic wasps that he thought that no benevolent creator could have been responsible for such cruelty. That creationists have adopted a business model based on lies (false witness) is also pretty ironic. $\endgroup$ – Karl Kjer Oct 24 '18 at 16:46
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    $\begingroup$ What is the source of your quotation? What is your question exactly? What attempt have you made to solve it yourself? Have you searched this site for related questions? $\endgroup$ – David Oct 24 '18 at 21:48
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There have been two answers that refer to the RNA World Hypothesis — which I do think is relevant — but both contain aspects I, personally, find unsatisfactory (as I commented originally). As this question has come up again from the Community, let me answer the question in a way that I, at least, find satisfactory.

I am only concerned with the biological part of the question:

“You need DNA to make RNA, and RNA to make DNA, so they had to come into existence at the same time.”

The question deals with something we do not know — the times at which DNA and RNA came into existence — so all we can deal with is the logic of the argument, i.e. is the conclusion of contemporaneous appearance necessarily true?

To refute that all that is needed is an alternative hypothesis for a sequential appearance that is consistent with biology and chemistry.

  • Contemporary biological systems exist in which DNA is not need to make RNA — namely RNA viruses. Although these depend on organisms (bacteria or eukaryotes) that have DNA genomes, their replication does not directly/mechanistically involve DNA. This, by itself, invalidates the first assertion (“you need DNA to make RNA”).
  • Turning to the origin of cellular life, which currently has exclusively DNA genomes, there is therefore no biochemical/mechanistic problem in envisaging that the ancestor of modern organism had an RNA genome at a time when pathways for synthesizing the precursors of DNA did not exist. Note that this does not require the other aspects of an RNA world (RNA, rather than protein, enzymes). These may be likely, but are not part of this argument.
  • So all that is required is a biochemically plausible hypothesis for the emergence of pathways for the synthesis of deoxyribose and thymidine, of enzymes to polymerize them, the switch to a (more stable and less error-prone) DNA genome, and the switch to this new genome encoding and transcribing the RNAs that are still necessary for protein synthesis and the like. I maintain that there is no reason in principle that this is not possible.

Whether or not the sequence of events was as in the scenario above, I argue that it demonstrates how RNA and DNA could have arisen at different times but given rise to the inter-dependent situation we see today, and demonstrates the basic flaw in the argument in the question.

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According to RNA world hypothesis at some point the organisms had RNA genome only and only later DNA and transcription machinery was built to protect the genome(DNA sits in the nucleus and does not interact much with others). RNA got both informations storage capability as well as the catalytic activity. Thus it can be concluded that at some point, RNA was the primary genome and RNA alone could let an organism survive due to its catalytic properties.

So to answer your question, it is a probability only but still, RNA appeared before DNA

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    $\begingroup$ Please note that the RNA world hypothesis doesn't have anything to do with nuclei - eukaryotes (and therefore the nucleus) for sure evolved much later than the DNA-RNA-protein system itself. $\endgroup$ – Nicolai Oct 24 '18 at 12:42
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I'm reading your questions as:

Since DNA and RNA co-depend on each other, which one existed first in the course of evolution

The honest answer to this is: we don't really know.

The RNA world hypothesis is a pretty good and also much studied and developed theory, but it's nonetheless a theory still. Even with solid experimental prove that a pure 'RNA world' can over time evolve to make DNA, won't let us know if it actually happened like this in the past or not.

A bit more background on why an intial "RNA world" from which DNA evolves at some point is theoretically possible:

In modern life forms genetic information is stored in DNA, then translated in RNA and a lot of functional elements are the resulting proteins. This is already a pretty complicated system so it was hypothesized that RNA might have one of the first molecules used for all of these steps. RNA can obviously store information (though not quite as long as DNA, since get degraded more quickly) and it can also have catalytic function, which is obvious from e.g. the ribosome, which still uses catalytic RNA units to build up all proteins.

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    $\begingroup$ The quotation in the question says nothing about which came first. It asserts both emerged together, presumably as an act of God, given the preamble. The question you want to answer has been asked and answered previously. $\endgroup$ – David Oct 24 '18 at 21:53
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    $\begingroup$ @David As far as i understand it the OP does not assert that DNA and RNA emerged together, but saw that statement somewhere and is now asking confirmation or further information on that - presumably from a scientific viewpoint given he is positng on this site (I'm judging from the question title and the 'who can shed light' part in the question). I purposely did not comment on the creation / act of God part since it has nothing to do with science. $\endgroup$ – Nicolai Oct 25 '18 at 22:34

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