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Periodical. Mills, D. R., R. L. Peterson, and Sol Spiegelman. "An Extracellular Darwinian Experiment with a Self-Duplicating Nucleic Acid Molecule." Proceedings of the National Academy of Sciences of the United States of America 58, 1 (July 1967): 217-224. Article. 8 Images.. Proceedings of the National Academy of Sciences of the United States of America