Early life may have emerged from a mixture of RNA and DNA building blocks, developing the two nucleic acids simultaneously instead of evolving DNA from RNA.
According to the RNA world hypothesis, early life used RNA to carry genetic information and perform biochemical catalytic reactions. Over time, DNA developed from RNA as the carrier of genetic information and proteins appeared as biochemical catalysts.
As RNA gave way to DNA, some think a mixture of nucleotide building blocks would have been inevitable. As these nucleotides connected to form strands, the thermodynamic and kinetic stability of pure RNA and DNA duplexes would drive these nucleic acids to accumulate in primitive cells, while less thermally stable complexes containing one strand of RNA and one strand of DNA fell apart.
To read more, click here.