preadaptations to speech

From: Marc Verhaegen (fa204466_at_skynet.be)
Date: 11/08/04 

Date: Mon, 8 Nov 2004 19:23:59 +0100

"Possible Preadaptations to Speech. A Preliminary Comparative Approach"
 Marc Verhaegen & Stephen Munro 2004
Human Evolution 19: 53-70

Abstract

Human language is a unique phenomenon and its evolutionary origins are
uncertain. In this paper we attempt to explore some of the preadaptations
that might have contributed to the origin of human speech.
The comparative approach we use is based on the assumption that all features
of a species are functional, and that all features can be compared with
those of other animals and correlated with certain lifestyles. Using this
method we attempt to reconstruct the different evolutionary pathways of
humans and chimpanzees after they split from a common ancestor.
Previous results from comparative studies suggest human ancestors may not
have evolved on the open African savannas as was once believed, but more
probably were coastal omnivores feeding on plant matter and easy to catch
invertebrates such as shellfish from beaches and shallow waters. Fossil and
archaeological data suggest this coastal phase occurred at the beginning of
the Pleistocene, when Homo ergaster-erectus dispersed between East-Africa,
North-Africa, South-Asia and Indonesia.
This paper presents comparative data suggesting the various human speech
skills may have had their origins at different times and may originally have
had different functions. Possible preadaptations to speech include, for
instance, musical skills present in a variety of primate species (sound
production); airway closure and breath-hold diving for collecting seafood
(voluntary breath control); and suction feeding adaptations for the
consumption of fruit juice or certain seafoods (fine control of
oropharyngeal movements). The different evolutionary pathways of chimpanzees
and humans might explain why chimpanzees lack language skills and why human
language is a relatively recent phenomenon.

Concluding Remarks

The combination of comparative and fossil data suggests that by about 1.8
million years ago human ancestors may have become more reliant on wading and
diving than on climbing.
A waterside mammal might be expected to have greater control of the lips,
tongue and throat muscles for seafood consumption, as well as voluntary
control of the airway and breathing musculature for swimming and diving.
This oral cavity and airway control might have been preadaptative to the
evolution of human speech, particularly in combination with the already
well-developed rhythmical, melodic and duetting abilities of our primate
ancestors.
A wading-and-diving lifestyle might have also required a different method of
communication. Traditional primate communication systems such as smell and
certain types of body language (such as posture, for example, though not
facial expression) may have been less effective in a semi-aquatic milieu
when compared to a purely terrestrial or arboreal one (Morgan 1997). Derek
Ellis (personal communication) notes "how well sound travels over water,
compared to being muffled in forests, and even compared to grassland.
Foraging beach and lagoon apes could separate quite widely and still remain
in contact by vocalising."
It is possible that the modifications to our ancestors' food and airway
entrances coincided with an early stage in the disproportionate expansion of
the human neocortex, in particular Area 4 (precentral) and Area 44 (Broca),
which control the fine movements of the mouth and throat muscles - whether
for singing, swallowing or diving. Humans, as opposed to chimpanzees and
other primates, have disproportionally large neocortical areas when compared
to the brain stem (e.g. Deacon 1997). Of these, the temporal and insular
areas (including the Areas 4, 44 and Wernicke), where sounds are produced,
processed and interpreted, seem to have undergone the greatest enlargement
(Semendeferi & Damasio 2000). Perhaps in this part of the brain, the
pre-existing functions of song production, food consumption and airway
control were integrated into a system that could produce voluntary and
articulated sounds, i.e. the beginnings of speech. The integration of this
voluntary sound production system with the symbolic powers that may have
already existed in primates (Savage-Rumbaugh 1986), might have been made
possible due to the extra brain tissue (association or integration cortex)
that developed during human evolution.

Our paper can be found in the AAT files
http://www.onelist.com/community/AAT

Relevant Pages