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The Mechanisms of Human Facial Expressions

The theory posits a series of radical evolutionary changes– the punctuations, as it were,
in punctuated equilibrium–rather than a continuous or unitary process. I do not rule out the
possibility, indeed the likelihood, of smaller graduated changes that might also have occurred
during the long period of human emergence; but judging from the anatomical and cultural
remains left by hominids and early humans, the most important evolutionary steps were
concentrated into a few transition periods when the process of change was greatly accelerated,
and these major transitions introduced fundamentally new capacities.
I have made certain hard choices–for instance, I have opted for a late-language model,
placing language near the end of the human evolutionary story rather than much earlier, as
Parker & Gibson (1979), and Bickerton (1990) have. For another, I have opted for a lexicallydriven model of language evolution, rather than placing the main emphasis on phonology as
Lieberman (1984) has, or on grammar as Bickerton (1990) has. In fact I have portrayed our
capacity for lexical invention as a single pivotal adaptation capable of evolving into an
instrument of sufficient power to support all of the higher aspects of language.
Moreover, I have postulated an early motor adaptation, intermediate between ape
cognition and language, that gives primacy to the unique motor and nonverbal cognitive skills of
humans. In this I am in basic agreement with Kimura (1976) and Corballis (1989; 1991) who
have also argued for an early motor adaptation that preceded speech. However I differ from these
two authors in that I am much less concerned with the issue of cerebral laterality, and more
focussed on the representational possibilities inherent in an early motor adaptation. Moreover, I
do not agree with them about the close qualitative linkage between language and serial motor
skill; I see the two as qualitatively different, albeit interdependent, adaptations.