Full Idea
There are three types of aristocracy, natural, elective and hereditary. The first is suited only to primitive peoples; the third is the worst of all governments; the second is the best, and this is aristocracy in the true sense of the word.
Gist of Idea
Natural aristocracy is primitive, hereditary is bad, and elective aristocracy is the best
Source
Jean-Jacques Rousseau (The Social Contract (tr Cress) [1762], III.05)
Book Reference
Rousseau,Jean-Jacques: 'The Basic Political Writings', ed/tr. Cress,Donald A. [Hackett 1987], p.181
A Reaction
Presumably he means what we call 'meritocracy', and it seems a bit optimistic to hope that democracy will deliver that. I don't think Plato would expect a democracy to elect his Guardians.