DNA, first isolated (though not yet named and described) in 1869, is the complex, self-replicating, double helix, chemical compound which carries the coded instructions for the development, functioning, growth and reproduction of all known organisms (and many viruses).
In discussions about thethe question arises as to when (and how) it first appeared in the (estimated) 4 billion year history of life on Earth.
The RNA World Hypothesis suggests that DNA evolved from RNA (a single stranded coded compound that can also self-replicate) but the details of exactly how this could happen are currently unclear.
The properties of RNA make the idea of the RNA world hypothesis conceptually plausible, though its general acceptance as an explanation for the origin of life requires further evidence.
See : Wikipedia
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