  What happens when a new social convention replaces an old one? While the
possible forces favoring norm change - such as institutions or committed
activists - have been identified since a long time, little is known about how a
population adopts a new convention, due to the difficulties of finding
representative data. Here we address this issue by looking at changes occurred
to 2,541 orthographic and lexical norms in English and Spanish through the
analysis of a large corpora of books published between the years 1800 and 2008.
We detect three markedly distinct patterns in the data, depending on whether
the behavioral change results from the action of a formal institution, an
informal authority or a spontaneous process of unregulated evolution. We
propose a simple evolutionary model able to capture all the observed behaviors
and we show that it reproduces quantitatively the empirical data. This work
identifies general mechanisms of norm change and we anticipate that it will be
of interest to researchers investigating the cultural evolution of language
and, more broadly, human collective behavior.
