Given high and approximately equal concentrations of nucleotides Adenine, Cytosine, Guanine and Thymine in aqueous solution, how readily could a simple DNA molecule form there?
I don't think this would auto-assemble into anything you would recognize as DNA. Nirenberg's famous auto-assembly of poly-uracyl RNA used a starter "sap", the crushed cytoplasm from a bacterium, along with the test tube of uracyl. See http://history.nih.gov/exhibits/nirenberg/HS4_polyU.htm
In my work (for a mental health line), I refer people to NIH quite often. Thanks for the link to that wonderful story, of which I was unaware until now.