To convey meaning, human language relies on hierarchically organized, long-
range relationships spanning words, phrases, sentences and discourse. As the
distances between elements (e.g. phonemes, characters, words) in human
language sequences increase, the strength of the long-range relationships
between those elements decays following a power law. This power-law
relationship has been attributed variously to long-range sequential organiz-
ation present in human language syntax, semantics and discourse structure.
However, non-linguistic behaviours in numerous phylogenetically distant
species, ranging from humpback whale song to fruit fly motility, also demon-
strate similar long-range statistical dependencies. Therefore, we hypothesized
that long-range statistical dependencies in human speech may occur indepen-
dently of linguistic structure. To test this hypothesis, we measured long-range
dependencies in several speech corpora from children (aged 6 months–
12 years). We find that adult-like power-law statistical dependencies are present
in human vocalizations at the earliest detectable ages, prior to the production of
complex linguistic structure. These linguistic structures cannot, therefore, be
the sole cause of long-range statistical dependencies in language