voluntary control and social transmissibility.Chimpanzee males often
give the long call together,during which they attempt to match the
acoustic characteristics of each other’s vocalizations.Moreover,single
males alter the acoustic structure of their calls when chorusing with dif-
ferent partners (Mitani and Brandt 1994;Arcadi 1996).This matching
tendency shows that call variants can be learned;more specifically,
learned not only early in ontogeny,but socially acquired in adulthood.
This is already a new level of communication.Barriers to Language Competence in Great Apes
This new,intermediate stage of language evolution in all probability
was present in the common ancestor of chimpanzees,bonobos,and
humans.However,specializations having taken place in lineages of
the former species did not make possible further languagelike
evolution.Neither finer articulation nor grammar evolved in their vocal
communication.Moreover,communicative meaning did not develop
further.
Signals of animal communication essentially express an emotional
state that can serve as motivation for the actions of others.However,in
the context of vocal territorial marking,a new type of meaning started
to evolve,namely,referential meaning.Most mammals mark territory
with physical or chemical signs,leaving a more or less permanent trace.
Such signs can be placed directly on the territory,and even in the absence
of the defender they inform other animals.When primates announce
their territory acoustically,the territory itself is not marked,but the pres-
ence and location of the defender are broadcast.Since different combi-
nations of available vocal elements result in interindividual differences
in call production,a special call pattern may identify the caller.Thus,the
indirect character of this territorial marking made possible the preser-
vation of this type of vocalization in great apes long after its original
function was lost.
Marking of social status or even individual identity is already a type
of reference.This suggests a different origin for referential communica-
tive signals relevant to the origin of language than that implied by the
often-cited varieties of predator alarm calls in vervet monkeys (Cheney
and Seyfarth 1990).As markers of individual identity,basic referential
vocalizations of great apes would be closer to the individual vocal ges-
tures of the highly encephalized bottle-nosed dolphins (Tyack 1993) than
to vervet alarm calls.Although vervet signals appear to refer to external
objects,their reference to objects instead of suggested modes of escape
remains to be proved.129 Social Organization