March 21, 1960
Dear Josh:
In reflecting on the unique tie between cells and DNA I was struck by the possible evolutionary implications for a common origin of cells.  If this is true I haven't found anyone who has said so and if it isn't so why not?  What is the flaw in my reasoning?  Your wide reading probably carried you to discussions I haven't seen.  Can you recall any comment on such a thought?
The RNA viruses only reinforce the notion for they show that other Geochemical coding schemes exist and yet in the wide variety of cellular systems analyzed thus far only DNA with -- in general the same four bases -- is the primary hereditary material.  If a number of cell types arose independently one might expect them to have different systems of biochemical coding.
Is this well known or incorrect?
We are getting some interesting thing, which I would like to talk over with you when our paths cross.
Best regards!
Roger