"when the great breakthroughs in science followed one after the other so rapidly"

World War Two necessitated various changes in medicine, and after the war there were many advances in almost all areas of medical science.  Perhaps the most crucial of these was the discovery of the structure of DNA in 1953.  In the world presented in Never Let Me Go, the advances have been even more remarkable, though they have brought with them serious moral dilemmas.

Medical advances since 1945