In 1962, John Gurdon, a zoology doctoral student at the University of Oxford, carries out an experiment that would refute a fundamental assumption of developmental biology at the time. Working with the African clawed frog Xenopus laevis, Gurdon extracts the nucleus from a fully differentiated intestinal cell — that is, a specialized adult cell, belonging to a specific tissue, that in theory had already irreversibly lost the ability to become any other cell type — and transplants it into an unfertilized egg from which the original nucleus had previously been removed via carefully calibrated ultraviolet irradiation. The modified egg develops normally into a tadpole and, in some cases, into a fertile adult frog, providing incontrovertible proof that the nucleus of a differentiated adult cell retains intact all the genetic information needed to direct an organism's complete development. The result directly contradicted the conclusions of Robert Briggs and Thomas King, who in 1952 had been the first to achieve nuclear transfer with early embryonic cells but had concluded the process was impossible with nuclei from already differentiated cells. Gurdon experimentally demonstrated that cell differentiation, far from being an irreversible genetic change, is a process of gene-expression regulation that can in principle be reversed by returning the nucleus to an appropriate embryonic environment. The term "cloning", originally taken from botany, was applied to an animal for the first time precisely as a result of this work. The finding laid the conceptual groundwork that, more than three decades later, would lead to the cloning of Dolly the sheep using the same nuclear transfer technique, and half a century later to Shinya Yamanaka's direct cell reprogramming via transcription factors, with whom Gurdon would ultimately share the Nobel Prize in 2012.