When most people think of cloning, their thoughts inevitably turn to science fiction movies or a sheep named Dolly. However, cloning has been around a lot longer than either of these would suggest. The word itself comes from the ancient Greek word for twig and was initially used to refer to plant grafting in the early 1900s. The word's meaning as it is used today, originated in the 1950s.
The scientists responsible for what is now thought of as cloning did not set out to create a genetically identical model of another organism—as clones are defined these days. They were simply trying to understand how an embryo develops into an adult. Nobel Laureate Hans Spemann began experimenting with salamander embryos in the 1930s. Using a piece of hair as a tool, he manipulated a dividing nucleus from a salamander embryo in such a way that he had two different nuclei in two different cells. The eventual result, two identical salamanders, caused Spemann to wonder if a nucleus from an adult creature could be placed in an embryo and divided in the same way.
Robert Briggs (1911-1983) and Thomas King (1921-2000) took up the quest several decades later. Briggs, apparently unaware of Spemann's work, also speculated that transplanting an adult nucleus into an enucleated fertilized egg would ultimately lead to a fully formed adult animal. He approached King about the microsurgical aspects of manipulating such minute amounts of matter, and soon the pair managed to implant nuclei from adult Leopard frogs into an enucleated egg. In 1952—forty-four years before Dolly became the first mammal to be cloned— they succeeded in cloning an organism for the first time, when the eggs they used went on to form tadpoles.
