Final answer:
Paul Berg proposed the four unique identifiers rule in 1975 for safe conduct of recombinant DNA research, establishing containment protocols for experiments with genetically modified organisms.
Step-by-step explanation:
The four unique identifiers rule was proposed by Paul Berg in 1975 as part of the guidelines for recombinant DNA research. This rule is not to be confused with any specific billing or identification rules, such as those in health or finance, which may also use the term 'unique identifiers'.
Berg's proposal was made during the Asilomar Conference on Recombinant DNA, which was convened to discuss the potential biohazards and regulation of biotechnology.
The four unique identifiers rule specifically referred to the physical and biological containment conditions required to ensure the safety of experiments involving genetically modified organisms.