1. Gesteland, R. & Atkins, J. F. The RNA World. The Nature of Modern RNA Suggests a Prebiotic RNA World (Cold Spring Harbor Laboratory Press, New York, 1993).
2. Joyce, G. F. & Orgel, L. E. in The RNA World (eds Gesteland, R. F. & Atkins, J. F.) 1–25 (Cold Spring Harbor Laboratory Press, New York, 1993).
3. Cairns-Smith, A. G. & Davies, C. J. in Encyclopaedia of Ignorance (eds Duncan, R. & Weston-Smith, M.) (Pergamon, Oxford, 1977).
4. Wittung, P., Nielsen, P. E., Buchardt, O., Egholm, M. & Nordén, B. Nature 368, 561–563 (1994).
5. Nielsen, P. E., Egholm, M., Berg, R. H. & Buchardt, O. Science 254, 1497–1500 (1991).