In November 1973, a five-page paper was published in the prestigious journal Proceedings of the National Academy of Sciences USA by Stanley Cohen, Annie Chang, Herb Boyer and Robert Helling from Stanford University in California. The title of the paper was “Construction of biologically functional plasmids in vitro”, and it described for the first time the production of an organism into which a DNA molecule had been introduced which consisted of DNA sequences from two different sources, joined together in the test tube. Although this work itself built on an earlier body of research, it may justifiably be seen as the paper which marked the birth of a scientific revolution which has continued to this day.
Great changes in science come about in different ways. Sometimes, they are the result of new concepts that transform our way of looking at things, or give us new insights into areas of knowledge which had previously been obscure. Such a revolution in biology had already occurred in the two decades before Cohen’s paper, with the realization that the fundamental stuff of inheritance is DNA, with the discovery of DNA’s remarkable structure, and with the unscrambling of the genetic code. Other dramatic changes in science have been more technical than conceptual, and are no less important for that. Cohen’s paper describes the first methods for manipulating DNA in ways that began to give the experimenters a measure of control over these molecules, hence enabling manipulation of the genetic properties of the organisms that contain them. Humans have, of course, been selectively breeding organisms for particular traits for millennia: domestication of wild plants for crops was a hugely successful early experiment in genetic engineering. But with the advent of what are commonly called recombinant DNA techniques, the degree to which we can produce predetermined genetic changes with high precision has grown to the point where now it is commonplace to make bacteria or plants that produce human proteins, to tinker with the basic structures of enzymes toalter their activity or stability, or to pull a single gene from the tens of thousands present in a human chromosome and identify within in it a single changed base that may give rise to a crippling genetic disease.