This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Kary Mullis has told the story of conceiving the polymerase chain reaction while driving a mountain road in Mendocino County, California, one night in 1983, working through the chemistry in his head as he drove: a way to make a short piece of DNA copy itself over and over, doubling with each cycle, until a single molecule became billions. Whatever the precise circumstances of that night, the idea belonged to real, ongoing work: Mullis was employed at Cetus Corporation in Emeryville, California, a biotechnology company doing exactly the kind of DNA synthesis and enzymology research the technique would need, and the record shows he first demonstrated PCR working successfully on 16 December 1983.
The technique itself is almost absurdly simple to describe and was, at the time, genuinely difficult to make reliable. Heat a DNA sample enough and its two strands separate; cool it and short synthetic primers can find and bind their matching sequence; warm it partway and an enzyme extends those primers into full copies of the target region. Repeat the cycle and the copies double each time, so twenty or thirty cycles turn a sample too small to detect into one large enough to sequence, test or match. Cetus's early instruments cycled the temperature by hand, moving tubes between water baths, until Taq polymerase, an enzyme isolated from bacteria that live in hot springs, replaced ordinary enzymes that fell apart at the temperatures the reaction needed and let the whole process run automated in a single machine.
Mullis shared the 1993 Nobel Prize in Chemistry for the invention, alongside Michael Smith, who was honored separately for a different DNA technique. PCR is now so embedded in molecular biology, genetic testing, forensic science and medical diagnostics that it is easy to forget it began as one researcher's idea about how a molecule that already knew how to copy itself might be made to do so on command, in a laboratory, on a schedule a scientist could control.