Soon after the discovery in 1970 of the first restriction enzyme by American microbiologist Hamilton Smith, it became possible to combine DNA from different sources into one molecule, producing recombinant DNA. Concern by scientists and lay people that some of this recombinant DNA might be harmful to humans prompted the research to stop until scientists could evaluate its risks.

In February 1975 over 100 internationally respected molecular biologists met at the Asilomar Conference Center in California. There, they decided upon a set of guidelines to be followed by all scientists doing recombinant DNA research. They considered each class of experiments, and assigned it a level of risk: minimal, low, moderate, or high. Each level of risk required a corresponding set of containment procedures designed to minimize the chance of vectors (carriers) containing recombinant DNA molecules from escaping into the environment where they could potentially harm humans or other parts...