  A most debated topic of the last years is whether simple statistical physics
models can explain collective features of social dynamics. A necessary step in
this line of endeavour is to find regularities in data referring to large scale
social phenomena, such as scaling and universality. We show that, in
proportional elections, the distribution of the number of votes received by
candidates is a universal scaling function, identical in different countries
and years. This finding reveals the existence in the voting process of a
general microscopic dynamics that does not depend on the historical, political
and/or economical context where voters operate. A simple dynamical model for
the behaviour of voters, similar to a branching process, reproduces the
universal distribution.
