I argued that it was important not to place too much reliance on any single piece of experimental evidence. It might turn out to be misleading, as th… - Francis Crick

A theory should not attempt to explain all the facts, because some of the facts are wrong.

Life, as we know it on earth, appears as a synthesis of two macromolecular systems. The proteins, because of their versatility and chemical reactivity, do all the work but are unable to replicate themselves in any simple way. The nucleic acids seem tailor-made for replication but can achieve rather little else compared with the more elaborate and better equipped proteins. RNA and DNA are the dumb blondes of the biomolecular world, fit mainly for reproduction (with a little help from proteins) but of little use for much of the really demanding work. The problem of the origin of life would be a great deal easier to approach if there were only one family of macromolecules, capable of doing both jobs, replication and catalysis, but life as we know it employs two families. This may well be due to the fact that no macromolecule exists which could conveniently carry out both functions, because of the limitations of organic chemistry; because, that is, of the nature of things.

"The dangerous man is the one who has only one idea, because then he'll fight and die for it."

[As quoted in The New Yorker, April 25, 2011]