Page i Artificial Life Page ii Complex Adaptive Systems John H. Holland, Christopher Langton, and Stewart W. Wilson, advisors Adaptation in Natural and Artificial Systems: An Introductory Analysis with Applications to Biology, Control, and Artificial Intelligence John H. Holland Toward a Practice of Autonomous Systems: Proceedings of the First European Conference on Artificial Life edited by Francisco J. Varela and Paul Bourgine Genetic Programming: On the Programming of Computers by Means of Natural Selection John R. Koza From Animals to Animats 2: Proceedings of the Second International Conference on Simulation of Adaptive Behavior edited by Jean-Arcady Meyer, Herbert L. Roitblat, and Stewart W. Wilson Intelligent Behavior in Animals and Robots David McFarland and Thomas Bösser Advances in Genetic Programming edited by Kenneth E. Kinnear, Jr. Genetic Programming II: Automatic Discovery of Reusable Programs John R. Koza Turtles, Termites, and Traffic Jams: Explorations in Massively Parallel Microworlds Mitchel Resnick From Animals to Animats 3: Proceedings of the Third International Conference on Simulation of Adaptive Behavior edited by Dave Cliff, Philip Husbands, Jean-Arcady Meyer, and Stewart W. Wilson Artificial Life IV Proceedings of the Fourth International Workshop on the Synthesis and Simulation of Living Systems edited by Rodney A. Brooks and Pattie Maes Comparative Approaches to Cognitive Science edited by Herbert L. Roitblat and Jean-Arcady Meyer Artificial Life: An Overview edited by Christopher G. Langton Page iii Artificial Life An Overview edited by Christopher G. Langton A Bradford Book The MIT Press Cambridge, Massachusetts London, England Page iv Fourth printing, 1998 First MIT Press paperback edition, 1997 © 1995 Massachusetts Institute of Technology All rights reserved. No part of this book may be reproduced in any form by any electronic or mechanical means (including photocopying, recording, or information storage and retrieval) without permission in writing from the publisher. Printed and bound in the United States of America. Library of Congress Cataloging-in-Publication Data Artificial Life: an overview / edited by Christopher G. Langton. p. cm.—(Complex adaptive systems) "A Bradford Book." Includes bibliographical references (p. ) and index. ISBN 0-262-12189—1 (HB), 0-262-62112-6 (PB) 1. Biological systems—Computer simulation. 2. Biological systems—Simulation methods. 3. Artificial Intelligence. I. Langton, Christopher G. II. Series. QH324.2.A74 1995 574'.01'13—dc20 94-46217 CIP Page v Contents Foreword vii Editor's Introduction ix Artificial Life as a Tool for Biological Inquiry 1 Charles Taylor and David Jefferson Cooperation and Community Structure in Artificial Ecosystems 15 Kristian Lindgren and Mats G. Nordahl Extended Molecular Evolutionary Biology: Artificial Life Bridging the Gap Between Chemistry and 39 Biology P. Schuster Visual Models of Morphogenesis 61 Przemyslaw Prusinkiewicz The Artificial Life Roots of Artificial Intelligence 75 Luc Steels Toward Synthesizing Artificial Neural Networks that Exhibit Cooperative Intelligent Behavior: 111 Some Open Issues in Artificial Life Michael G. Dyer Modeling Adaptive Autonomous Agents 135 Pattie Maes Chaos as a Source of Complexity and Diversity in Evolution 163 Kunihiko Kaneko An Evolutionary Approach to Synthetic Biology: Zen and the Art of Creating Life 179 Thomas S. Ray Beyond Digital Naturalism 211 Walter Fontana, Günter Wagner, and Leo W. Buss Learning About Life 229 Mitchel Resnick Books on Artificial Life and Related Topics 243 David G. Stork Computer Viruses as Artificial Life 249 Eugene H. Spafford Page vi Genetic Algorithms and Artificial Life 267 Melanie Mitchell and Stephanie Forrest Artificial Life as Philosophy 291 Daniel Dennett Levels of Functional Equivalence in Reverse Bioengineering 293 Stevan Hamad Why Do We Need Artificial Life? 303 Eric W. Bonabeau and Guy Theraulaz Index 327 Page vii Foreword Christopher G. Langton Editor-in-Chief Santa Fe Institute This book is intended as a high-level index to the Artificial Life enterprise. It provides a point of entry to the field for both the newcomer and the seasoned researcher alike. The essays in this book introduce the many subdisciplines of Artificial Life and organize a large body of citations to the literature in the field. I would recommend this book as an excellent text for a graduate seminar on Artificial Life, accompanied by readings drawn from the citations tailored to the professor's or the student's interests. As Artificial Life is a highly interdisciplinary field, drawing researchers from across the academic and scientific spectrum, the authors have made an extra effort to make their essays comprehensible to readers from outside their own particular disciplines. They have defined technical terms where needed and provided background motivation for techniques and approaches that might otherwise require in- depth knowledge of some highly specialized body of theory. Thus, this book should prove accessible to anyone with a moderate background in the sciences. I have made a special effort to include not only scientific and engineering papers, but also reviews of some of the philosophical and social issues, as it is just as important to understand how a field fits into the web of science and society as it is to understand the internal details of the field. CHRISTOPHER G. LANGTON Page ix Editor's Introduction Christopher G. Langton Editor-in-Chief Santa Fe Institute This book consists of the first three issues of Artificial Life. These initial issues contain a special set of overview articles contributed by members of the editorial board of the journal. In these articles, each editor has attempted to review his or her own thread of special interest within the broad and diverse tapestry of research efforts that have come to be associated with the term "Artificial Life." In general, each article contains a bit of history on a particular research topic, a review of some of the more important problems, a description of the most promising techniques and methods for addressing these problems, and a view toward the future, with suggestions of the impact that Artificial Life techniques will have on our understanding of the biological phenomena under study. The primary purpose of this initial set of overview articles is to "prime the pump" for future research in the field of Artificial Life, thereby stimulating future contributions to the journal itself. They are also intended to help define and delineate the field of Artificial Life more thoroughly than has been done until now. The term Artificial Life literally means "life made by humans rather than by nature." As you will see in these articles, Artificial Life is many things to many people, and I will not attempt to give a concise definition of it here. In fact, Artificial Life is not yet ready to be constrained by quick and short definitions—the field is still in the process of defining itself, as is proper for any new discipline. The articles in this volume carefully stake out claims to certain areas of study, but there is far more intellectual territory out there waiting to be discovered and laid claim to. Among all of the things that Artificial Life is or will come to be, however, it is probably safe to say that the field as a whole represents an attempt to increase vastly the role of synthesis in the study of biological phenomena. Synthesis has played a vital role in the grounding of many scientific disciplines, because it extends the empirical database upon which the theory of the discipline is built beyond the often highly accidental set of entities that nature happened to leave around for us to study. Take the field of chemistry as an example: In the earliest stages of research into the constitution of matter, people took stock of the kinds of chemical compounds that nature had provided them with, catalogued and classified them, analyzed them by taking them apart into their constituent pieces, and then analyzed the pieces. This was fine as far as it went, but there was a great deal of accident and historical process involved in the determination of the kinds of chemical compounds that nature happened to leave around for study, and it would have been very difficult to observe the law-regularities in the highly irregular and unique set of compounds that early researchers happened to have available for study. It was only through the process of synthesis—putting the constituent pieces of matter together in new and different ways—that researchers were able to extend the set of chemical compounds available for study far beyond the irregular set provided to them by nature. It was only within the context of this much larger set of "possible" chemical compounds that researchers were able to see beyond the accidental nature of the "natural" chemical compounds, and glimpse the regularities in Page x the constitution of matter. To have a theory of the actual, it is necessary to understand the possible. The situation is much the same in biology. The set of biological entities provided to us by nature, broad and diverse as it is, is dominated by accident and historical contingency. We trust implicitly that there were lawful regularities at work in the determination of this set, but it is unlikely that we will discover many of these regularities by restricting ourselves only to the set of biological entities that nature actually provided us with. Rather, such regularities will be found only by exploring the much larger set of possible biological entities. Many biologists have speculated wistfully about "rewinding the tape" of evolution, starting the process over again from slightly different initial conditions. What would emerge? What would be the same? What would be different? We sense that the evolutionary trajectory that did in fact occur on earth is just one out of a vast ensemble of possible evolutionary trajectories—each leading to a biology that could have happened in principle, but didn't in fact solely for reasons of accident combined with common genetic descent.