While examining the evolution of
language it is advantageous to study the evolution of speech independently.
While speech is the default modality of language, language has more than one means
of transmission and therefore when examining language evolution it is
worthwhile examining the evolution of the differing modalities and what makes
them special to humans. The evolution of speech can be broken down into a
number of parts: the evolution of speech production and articulation, which
involves exploring the changes in the vocal tract and neural control of
articulators; the ability for vocal learning and imitation, which is overtly
seen in children learning language; and the evolution of speech perception,
which involves examining changes to the auditory system.
The aim of this essay is to explore
the human capacity for speech production and perception in regards to its
unique properties and the selection pressures which lead to their evolution. To
achieve this aims the essay adopts the following structure: section two deals
with the evolution of the vocal tract in comparison to our common ancestors; section
three explains the changes in neurological control which aid speech
articulation; section four looks toward vocal imitation and how this plays a
role in speech production and perception; finally section five examines the
links between production and perception and how speech perception has evolved.
Vocal Tract Changes
Argued to be one of the most
important distinguishing features of human vocalization is the use of formants.
When looking at both human and nonhuman primate vocalisations, one of the
largest differences seen is that humans rely heavily on formants for acoustic
production (Fitch 2000: 260). Formants are best described by Gamba, Torti,
Colombo and Giacoma (2012: 289) as the acoustic frequency peaks that are
produced by a spectrogram when recording speech. These peaks correspond with
the shape of the vocal tract during speech production. When the airflow
vibrates through the vocal tract it is influenced by its shape and length. The
differing formant frequencies produced equate to the different sounds produced
by the different articulators in the vocal tract.