Semiotic Combination in Pan: Evolutionary implications of proto-syntax

Heidi Lyn1, Patricia Greenfield2, and E. Sue Savage-Rumbaugh3
1Wildlife Conservation Society, 2UCLA, 3Language Research Center

hlyn@wcs.org

Over twenty years of research at the Language Research Center have
demonstrated that bonobos can learn to comprehend spoken English at the
level of a two-and-a-half year old human child without explicit training
(E.  Sue Savage-Rumbaugh, 1986; E.  Sue Savage-Rumbaugh, McDonald,
Sevcik, Hopkins, & Rupert, 1986; E.  Sue Savage-Rumbaugh et al., 1993;
E.  Sue Savage-Rumbaugh, Shanker, & Taylor, 1998).  In addition, these
bonobos could utilize visuographic symbols (lexigrams) on a printed
keyboard to communicate with researchers.  Earlier research with
chimpanzees (Pan troglodytes) in more formalized language training
programs had been less successful (Gardner & Gardner, 1969; Hayes, 1951;
Kellogg & Kellogg, 1933; Rumbaugh, 1977; E.  S.  Savage-Rumbaugh,
Rumbaugh, Smith, & Lawson, 1980; Terrace, 1979).  Because the research
at the Language Research Center included a different species - bonobos
(Pan paniscus) and a different rearing environment (including extensive
early language enrichment, but no formal training) a co-rearing study
was initiated.  Rearing a bonobo (Panbanisha) and a chimpanzee
(Panpanzee) together demonstrated that the primary source of earlier
chimpanzee-bonobo communication differences was rearing environment,
rather than species-based genetic differences (Brakke & Savage-Rumbaugh,
1995, 1996; Williams, Brakke, & Savage-Rumbaugh, 1997). 

This paper focuses on the spontaneous lexigram and gestural symbolic
productions of these co-reared apes and compares them to another
symbol-competent bonobo and productions from human researchers who were
the apes' primary caregivers.  Specifically, we report on two-element
combinations (two lexigrams or one lexigram plus one gesture) produced
by the apes throughout five months of the study period.  All productions
during the study period were instances of spontaneous two-element
combinations, which were then coded according to their semiotic
functions, following the procedures in Brown (1973) and Greenfield and
Savage-Rumbaugh (1990; 1991).  The results demonstrate the construction
of communicative conventions: shared norms for combining symbols that
were shared by either the two co-reared apes, all three language
competent apes or one of the apes and the researchers.  For example, all
three apes and the human researchers were more likely to order an action
before an agent, rather than an agent before an action ("open cooler"
rather than "cooler open").  These shared norms were statistical, not
absolute, which is true of human children as well (e.g., Bowerman, 1973;
Goldin-Meadow & Mylander, 1984).  Ordering conventions applied to
combinations consisting of lexigram plus gesture, as well as
combinations consisting of two lexigrams.  These findings are in
contrast to earlier reports of language-trained apes which did not find
ordering conventions in their productions (Terrace, Petitto, Sanders, &
Bever, 1979, 1980). 

Additionally, a bonobo shared more communicative conventions with his
co-reared chimpanzee than with another bonobo who had not shared the
same rearing environment - emphasizing the importance of social
interactions and early environment in forming communicative conventions,
over species-specific predispositions.  However, this study offers no
evidence to support the knowledge of formal syntactic structure in any
of the apes.  It is therefore possible that the ability to create
communicative conventions at the level of proto-syntax was present in
the common ancestor of chimpanzees, bonobos, and humans five million
years ago (Byrne, 1995) and subserved the subsequent evolution of
communication in each species (Gannon, Holloway, Broadfield, & Braun,
1998). 



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