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A Saltational Approach for the Evolution of Human Cognition and Language

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A Saltational Approach for the Evolution of Human Cognition and Language A Saltational Approach for the Evolution of Human Cognition and Language Susan J. Lanyon A thesis submitted in fulfillment of the requirements for the degree of Doctor of Philosophy. University of New South Wales June 2010 COPYRIGHT, AUTHENTICITY, and ORIGINALITY STATEMENT I hereby grant the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstract International. I have either used no substantial portions of copyright material in my thesis or I have obtained permission to use copyright material; where permission has not been granted I have applied/will apply for a partial restric- tion of the digital copy of my thesis or dissertation, and I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any minor variations in formatting, they are the result of the conversion to digital format, and I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgment is made in the thesis. Any con- tribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project’s design and conception or in style, presentation and linguistic expression is acknowledged. Signed ................................... Date ............................... iii Abstract This thesis takes a saltational approach to the evolution of both human anatomy and cognition. I argue that the cognitive traits that appear to be unique to humans emerged in a discontinuous fashion because of a radical re-organization of brain architecture. I accept Darwin’s founda- tional tenet that evolution proceeds by descent with modification, but I also give credence to the idea that emergent novelty can arise at crucial levels within complex systems. Despite many years of experi- ments with monkeys and apes, there are no obvious precursors for any of the underlying systems currently supporting human cognition that could have evolved gradually over time. Our hominid ancestors did not evolve as a ‘trend’ toward modern human anatomy, nor did they grad- ually ‘evolve’ human-like cognition and language. Homo sapiens seems to have emerged in one saltatory ‘event’, most likely in Africa, around 120,000 years ago. Evidence from paleontology, archaeology and genet- ics is garnered to support this claim. As we find more and more juvenile hominid fossils, evidence mounts that this event can be accounted for by the neotenous retention of our immediate hominid ancestor’s juve- nile anatomy. I argue that the anatomical traits that we equate with H. sapiens, especially those supporting our ability for speech or sign, were not gradually ‘adapted’ to ‘serve’ this emergence in neo-Darwinian fash- ion. I also contend that traits considered unique to human cognition, including language, arose due to the massive increase in interconnec- tivity and non-volatile memory within the human brain made possible by this saltatory event. iv Contents 1 Introduction 1 1.1 Cognition and Evolution . 1 1.2 The Saltationist Approach . 4 1.2.1 Evolutionary Precursors . 4 1.2.2 Evolutionary Development . 7 1.2.3 Paedomorphic Hominids . 10 1.2.4 Archaeology - Saltation and Stasis . 14 1.3 The Evolution of Language . 17 1.4 Summary . 18 2 Problems with Gradualism 21 2.1 Introduction . 21 2.2 Darwin’s Legacy . 23 2.3 Neo-Darwinian Evolution . 28 2.4 Natural Selection and Complexity . 30 2.5 Adaptation to Changing Conditions of Life . 34 2.6 Adaptation and Speciation . 38 2.7 Natural Selection as Conservator . 41 2.8 Brain Evolution . 42 2.9 Summary . 54 3 Saltationism and Evolutionary Developmental Biology 57 3.1 Introduction . 57 3.2 Developmental Systems . 62 3.2.1 Homeobox – Hox Genes and Development . 65 3.2.2 Paedomorphism . 67 3.3 Summary . 71 v vi CONTENTS 4 Paleontological Evidence 73 4.1 Introduction . 73 4.2 Heterochrony and Hominid Evolution . 76 4.2.1 Neoteny and Hominid Evolution . 77 4.2.2 No Trends . 79 4.3 Bipedalism . 81 4.3.1 Primate Bipedalism . 83 4.3.2 Hominid Bipedalism . 84 4.4 Hands with Precision Grip . 93 4.5 Primate Crania - Face, Jaws and Teeth . 95 4.6 Evolution of the Vocal Tract . 101 4.7 Brain Growth and Size . 104 4.7.1 The Australopithecines . 105 4.7.2 H. erectus Brains . 106 4.7.3 Homo floresiensis . 110 4.8 Summary . 112 5 Archaeological Evidence 117 5.1 Introduction . 117 5.2 Stone Tools . 120 5.2.1 Chimpanzee tool use . 123 5.2.2 Orangutan tool use . 123 5.2.3 The First Hominid Stone Tools . 124 5.2.4 Homo erectus Stone Tools . 126 5.2.5 Neandertal Stone Tools . 129 5.3 Language and Stone Tools . 130 5.3.1 Anatomically Modern Humans’ Tools . 134 5.3.2 Homo sapiens Artefacts and the Emergence of Symbolic Behaviour . 135 5.4 Burials . 138 5.4.1 Neandertal Burials . 139 5.4.2 Final Words on Hominid Burials . 141 5.5 Fire . 143 5.6 Shelter . 145 5.7 Environmental management . 146 5.8 Summary . 148 CONTENTS vii 6 Genetics and Development 151 6.1 Introduction . 151 6.2 Relationships - Great Apes and Humans . 153 6.3 Neurogenesis . 156 6.4 The Human Brain - Escaping Constraints . 157 6.4.1 The Importance of White Matter . 159 6.4.2 Language Genes? . 163 6.5 Summary . 165 7 The Evolution of Language 167 7.1 Introduction . 167 7.2 Language for Communication . 170 7.2.1 Gradual Evolution of Language for Communication 171 7.2.2 Symbolic systems . 176 7.2.3 A Theory of Mind . 179 7.2.4 Cooperation and Collaboration . 187 7.2.5 Social intelligence . 190 7.2.6 Pragmatics . 197 7.2.7 Knowledge of Causality . 199 7.2.8 Enhanced Memory . 202 7.3 Precursors of Communicative Systems . 203 7.4 Animal Calls . 206 7.5 From Animal Calls to Protolanguage . 215 7.5.1 Imitation . 216 7.5.2 Gestural Imitation . 218 7.6 Recapitulation - Acquisition and Evolution . 225 7.7 Language as Exaptation . 234 7.7.1 Language for Thought . 239 7.7.2 Language only with H. sapiens . 240 7.8 Summary . 241 8 Conclusion 243 Bibliography 251 Author Index 274 viii CONTENTS Chapter 1 Introduction 1.1 Cognition and Evolution Much of the current work in the Cognitive Sciences touches on the ques- tion of what makes humans unique, and how our complex traits have evolved. There is no doubt that the mainstream view of the evolution of human cognition is one of gradual development (hereafter, ‘gradual- ism’), but I join with the growing number of scholars who find gradu- alism untenable and are turning to saltationism as a more plausible approach. I have yet to find an account of human cognitive evolution, however, that takes the saltationist approach to the point of arguing, as I do in this thesis, that all of the unique cognitive traits attributed to hu- mans arose as the consequence of one crucial mutation, which radically altered the architecture of the ancestral primate brain. The aim of this thesis is to show that the available evidence of the evolutionary history of hominids and human cognition is more satis- factorily accounted for under a saltationist approach. I argue that the really important changes in the evolutionary development of hominids, as evidenced by the paleontological record, can be accounted for by non- adaptational processes, and that natural selection does not, and cannot, explain the sudden emergence of these developments. I further argue that modern humans1 did not evolve as a gradual ‘trend’ toward be- coming ‘human’ after the split from their Great Ape ancestor. Most of 1Wherever I use the term “modern human”, I am referring to the species Homo sapiens. 1 2 CHAPTER 1. INTRODUCTION the anatomical changes that have taken place in our hominid ancestors (evidenced by the paleontological record) are merely variations of the regular Great Ape Bauplan. Many of the anatomical traits that we use to define ‘human’ can already be found in the fossils of extinct primates. I use this fact to argue against ‘special pleading’ proposals that attempt to link anatomical changes with cognitive advances in our hominid an- cestors. Anatomical traits, like bipedalism, hands with precision grip and variations in dentition can all be accounted for by minor changes in developmental processes that have emerged suddenly and have been followed by millions of years of stasis. Many scholars have proposed that traits like bipedalism, a large brain, language, social complexity, tool use, and other characteristics of humans, must have evolved in tandem during the evolutionary his- tory of our hominid ancestors. We find, for example, suggestions like bipedalism is the key to understanding human brain evolution (Falk, 1992, p.
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