Superstrings from theories with N>1 world-sheet supersymmetry
  String theories with (N,N') local world-sheet supersymmetries are related to each other by marginal deformations. This connects N=1 and N=0 theories in which the target-spaces are interpreted as space-times, N=2 theories in which the target spaces can be interpreted as world-volumes, and theories with $N\ge 3$, in which the central charge vanishes -- theories with zero target-space dimensions. 
Laurent Baulieu, Michael B. Green, Eliezer Rabinovici