Kulturkreis was a theory which postulated that all human ideas, technology and culture could be traced back to an ideal source and could be used to argue for the concept of racial purity.
The theory, the name of which could not be translated by the Unbound Doctor's TARDIS because neither he nor Bernice Summerfield had an equivalent term, was supported by the Nazis and the Kulturkreis Institute and became obsolete following the Second World War. (AUDIO: Übermensch)