Abstract
The emergence of syntax during childhood is a remarkable example of how complex correlations unfold in nonlinear ways through development. In particular, rapid transitions seem to occur as children reach the age of two, which seems to separate a two-word, tree-like network of syntactic relations among words from the scale-free graphs associated with the adult, complex grammar. Here, we explore the evolution of syntax networks through language acquisition using the chromatic number, which captures the transition and provides a natural link to standard theories on syntactic structures. The data analysis is compared to a null model of network growth dynamics which is shown to display non-trivial and sensible differences. At a more general level, we observe that the chromatic classes define independent regions of the graph, and thus, can be interpreted as the footprints of incompatibility relations, somewhat as opposed to modularity considerations.
Highlights
The origins of human language have been a matter of intense debate
Maybe the most defining and defeating trait is its virtually infinite generative potential: words and sentences can be constructed in recursive ways to generate nested structures of arbitrary length [3,5]. Such structures are the product of a set of rules defining syntax, which are extracted by human brains through language acquisition during childhood & 2018 The Authors
Syntax is one aspect of the whole: semantic and phonological aspects need to be taken into account, and they are all embedded in a cognitive, brain-embodied framework [35]
Summary
The origins of human language have been a matter of intense debate. Language is a milestone in our evolution as a dominant species and is likely to pervade the emergence of cooperation and symbolic reasoning [1,2,3,4]. Statistical physicists have approached the problem of language evolution showing, for example, that non-trivial patterns are shared between language inventories—collections of words—and some genetic and ecological neutral models [9] (see [10] and references therein) Most of these models do not make any assumption about the role played by actual interactions among words, or, more generally, linguistic units, which largely define the nature of linguistic structures. The aim of using the chromatic number comes from the intuition that syntactic relations do not glue elements for free but display consistent rules of compatibility/ incompatibility among lexical elements This may seem obvious at the level of the sentence analysis, but to extrapolate how these combinatorial rules among different classes of elements work at the global system level is a hard task, and even harder, if we want to do it quantitatively. This is, to the best of our 3 knowledge, the first time that such transitions have been reported in a real system
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