harnad@phoenix.Princeton.EDU (S. R. Harnad) (02/09/90)
Below is the abstract of a forthcoming target article to appear in
Behavioral and Brain Sciences (BBS), an international, interdisciplinary
journal that invites Open Peer Commentary on important and
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Natural Language and Natural Selection
Steven Pinker
and
Paul Bloom
Department of Brain and Cognitive Sciences
Massachusetts Institute of Technology
Abstract
Many have argued that the evolution of the human language faculty
cannot be explained by Darwinian natural selection. Chomsky and Gould
have suggested that language may have evolved as the byproduct of
selection for other abilities or as a consequence of unknown laws of
growth and form. Others have argued that a biological specialization
for grammar is incompatible with Darwinian theory: Grammar shows no
genetic variation, could not exist in any intermediate forms, confers
no selective advantage, and would require more time and genomic space
to evolve than is available. We show that these arguments depend on
inaccurate assumptions about biology or language or both. Evolutionary
theory offers a clear criterion for attributing a trait to natural
selection: complex design for a function with no alternative processes
to explain the complexity. Human language meets this criterion: Grammar
is a complex mechanism tailored to the transmission of propositional
structures through a serial interface. Autonomous and arbitrary
grammatical phenomena have been offered as counterexamples to the claim
that language is an adaptation, but this reasoning is unsound:
Communication protocols depend on arbitrary conventions that are
adaptive as long as they are shared. Consequently, the child's
acquisition of language should differ systematically from language
evolution in the species; attempts to make analogies between them are
misleading. Reviewing other arguments and data, we conclude that there
is every reason to believe that a specialization for grammar evolved by
a conventional neo-Darwinian process.
Keywords: Language, Evolution, Language Acquisition, Natural Selection,
Grammatical Theory, Biology of Language, Language Universals,
Psycholinguistics, Origin of Language
Table of Contents
1. Introduction 2
2. The Role of Natural Selection in Evolutionary Theory 5
2.1. Nonselectionist Mechanisms of Evolutionary Change 6
2.2. Limitations on Nonselectionist Explanations 7
2.3. Two Issues that are Independent of Selectionism 13
2.3.1. Gradualism 13
2.3.2. Exaptation 14
3. Design in Language 16
3.1. An Argument for Design in Language 16
3.2. Is the Argument for Language Design a Just-So Story? 21
3.3. Language Design and Language Diversity 25
3.4. Language Design and Arbitrariness 28
3.4.1. Inherent Tradeoffs 29
3.4.2. Parity in Communications Protocols 31
3.4.3. Arbitrariness and the Relation Between Language Evolution 34
and Language Acquisition
4. Arguments for Language Being a Spandrel 37
4.1. The Mind as a Multipurpose Learning Device 37
4.2. Constraints on Possible Forms 38
5. The Process of Language Evolution 41
5.1. Genetic Variation 41
5.2. Intermediate Steps 43
5.2.1. Nonshared Innovations. 43
5.2.2. Categorical Rules. 45
5.2.3. Perturbations of Formal Grammars. 46
5.3. Reproductive Advantages of Better Grammars 48
5.3.1. Effects of small selective advantages. 49
5.3.2. Grammatical complexity and technology. 50
5.3.3. Grammatical complexity and social interactions. 51
5.3.4. Social use of language and evolutionary acceleration. 52
5.4. Phyletic Continuity 54
6. Conclusion 56
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Stevan Harnad Department of Psychology Princeton University
harnad@clarity.princeton.edu srh@flash.bellcore.com
harnad@elbereth.rutgers.edu harnad@pucc.bitnet (609)-921-7771