"Two developments in the late 1960s and early 1970s set the stage for supergravity. First the standard model took shape and was decisively confirmed by experiments. The key theoretical concept underlying this process was gauge symmetry, the idea that symmetry transformations act independently at each point of spacetime. ... The other development was global (also called rigid) supersymmetry ... It is the unique framework that allows fields and particles of different spin to be unified in representations of an algebra system called a superalgebra."