In 1983, Kary Mullis invented a process he called PCR, which solved a core problem in genetics: How to make copies of a strand of DNA you are interested in.

The existing methods were slow, expensive and imprecise. PCR turns the job over to the very biomolecules that nature uses for copying DNA: two "primers" that flag the beginning and end of the DNA stretch to be copied; an enzyme called polymerase that walks along the segment of DNA, reading its code and assembling a copy; and a pile of DNA building blocks that the polymerase needs to make that copy.

As he wrote later in Scientific American:

"Beginning with a single molecule of the genetic material DNA, the PCR can generate 100 billion similar molecules in an afternoon. The reaction is easy to execute. It requires no more than a test tube, a few simple reagents and a source of heat. The DNA sample that one wishes to copy can be pure, or it can be a minute part of an extremely complex mixture of biological materials. The DNA may come from a hospital tissue specimen, from a single human hair, from a drop of dried blood at the scene of a crime, from the tissues of a mummified brain or from a 40,000-year-old wooly mammoth frozen in a glacier."