  The evolution of human language allowed the efficient propagation of
nongenetic information, thus creating a new form of evolutionary change.
Language development in children offers the opportunity of exploring the
emergence of such complex communication system and provides a window to
understanding the transition from protolanguage to language. Here we present
the first analysis of the emergence of syntax in terms of complex networks. A
previously unreported, sharp transition is shown to occur around two years of
age from a (pre-syntactic) tree-like structure to a scale-free, small world
syntax network. The nature of such transition supports the presence of an
innate component pervading the emergence of full syntax. This observation is
difficult to interpret in terms of any simple model of network growth, thus
suggesting that some internal, perhaps innate component was at work. We explore
this problem by using a minimal model that is able to capture several
statistical traits. Our results provide evidence for adaptive traits, but it
also indicates that some key features of syntax might actually correspond to
non-adaptive phenomena.
