Is it not reasonable to anticipate that our understanding of the human mind
would be aided greatly by knowing the purpose for which it was designed?
Williams 1966, p. 16
We have been gratified by the reception given the first edition of this book; it is being used at a wide variety of institutions, both as an introduction to psychology and as a text for advanced courses on evolutionary psychology. We are especially pleased to hear that students have been enthusiastic in their reaction to it.
We have made some changes in organization in response to suggestions from users. The first four chapters have been reorganized into three, and their contents have been streamlined so that readers can begin consideration of substantive issues in psychology sooner. Certain topics, such as kin selection and reciprocal altruism, that were previously covered in the introductory chapters, have been delayed until they are needed to parse particular questions about human behavior.
Some chapters have been reordered. Although not formally demarcated as such, the first three chapters may be thought of as Part I. Part II consists of sensation and perception, consciousness, and motivation and emotion, for better continuity. Part III is made up of cognition and learning. The order of these two chapters has been reversed to emphasize the connection between perception, consciousness, and cognition. Part N is made up of individuality, health, and abnormal. The final section, Part V, groups together four related chapters: mating, families and development, social, and culture.
The explosive growth of evolutionary psychology has led us to add many new references. We have striven to reflect the development of the field without attempting to cover all the exciting new material. Rather, we continue our plan of considering in sufficient depth representative developments in the field. Thus we have not included some work (including our own!) that is well deserving of a place in this book. We apologize to all who have been thus excluded.
The Trail Markers have been popular with readers, and many new ones have been added.
In one important way, this book is very different from other introductory psychology texts. Traditional psychology largely ignores the question of what the mind is for. This oversight puts traditional psychology seriously out of step with the rest of the life sciences, where design-for-a-function is recognized as the normal result of evolution by natural selection. You may hesitate, but there is little room for doubt: Psychology is a life science. It studies the behavior of living things, not rocks or stars or electrons. The theory of evolution has inspired countless thousands of discoveries throughout the life sciencesin physiology, ecology, medicine, and the like. It is time to consider what this theory can offer to psychology.
In a sentence, natural selection shapes organisms by preserving those chance genetic variants that aid survival and reproduction. Contemporary biologists are convinced that every single species, including our own, owes its present form to a long history of natural selection. Their conclusion applies with equal force to every organ system; the mind and the behaviors it fosters are in no way exempt from this process. Thus our working assumption is that human psychology was designed by evolution, over millions of years, to solve the various challenges that faced our ancestors in their struggles to survive and reproduce.
We have chosen to write an introductory textbook for one simple reason: Evolutionary psychology is not a specialized subfield of psychology, such as personality psychology or abnormal psychology. Instead, it is a different way of thinking about the entire field. Its insights and methods should be the groundwork for the study of psychology, not an afterthought. Our goal is that after reading this text, students will be able to think like evolutionists, not only about human behavior but also about a wide range of related matters.
But what of traditional psychology? Let us be clear. Traditional psychology is a rich and vital field, but we have two general criticisms of it. First, because traditional psychology has no overarching theory of what we call "mind design," it can only take a. trial-and-error approach to discovering the mind's operating principles. Unfortunately, trial and error is slow and inefficient, and it has led to some spectacular blind alleys, such as Freudian theory. Second, most of traditional psychology's reliable findings about perception, thought, learning, motivation, social behavior, and the like are more sensible and more informative when they are interpreted in an evolutionary framework. For example, longstanding debates, such as the one over nature versus nurture, are illuminated and usefully resolved by evolutionary thinking.
Thus we begin in Chapter 1 by mapping the differences between evolutionary psychology and the more traditional nonevolutionary approach. Evolutionary psychologists and traditional psychologists often differ in how they develop their theories, in the kinds of questions they pose, and in the sorts of statements they accept as valid answers. There is an old saying that you can't understand what a person is saying unless you know who he's arguing against. Let's be explicit then; in a real sense we are arguing against many of the assumptions and interpretations (but few of the findings) of traditional psychology.
Studying psychology from an evolutionary viewpoint requires a clear understanding of the theory of evolution. Thus one of our key missions is to explain what evolution is (and isn't), and what it can (and cannot) do. These matters are the focus of chapters 2 and 3. There may be a temptation on the part of both students and professors to skip or deal briefly with these chapters in order to get on to the "meat" of the coursepsychology. We beg you not to yield to the temptation! Every high school graduate "knows what evolution is." But most harbor serious misconceptions: Evolution always fosters what is good for the species; because of their basis in genes, evolved traits are fixed and unresponsive to experience; species can usefully be arranged on a ladder from lower to higher. Wrong; wrong; and wrong again! According to a large majority of modern evolutionists, all three of these ideas are dangerously off the mark. There are also many other pitfalls and misconceptions that must be discussed before evolutionary theory can be productively applied to the study of psychology or to any other set of questions. Thus a thorough grasp of the basics of modern evolutionary theory, especially as it relates to behavior, is essential to a full appreciation of the argument and evidence in this book.
The remaining chapters, 4 through 15, each treat one of the central topics of modern psychology. The topics include sensation and perception, development, learning, cognition, social psychology, abnormal psychology, motivation, individual differences and several others. In each of these chapters, our focus is not on reviewing the entire literature, either from a traditional or an evolutionary perspective. Instead, by discussing several examples in each chapter, we try to show what evolutionary psychology is, how it reorients the study of mind and behavior, and how genuinely novel its conclusions can be. Our goal in exemplifying the evolutionary approach over such a wide range of topics is twofold. Of course, we intend that each reader will take away a richer understanding of human behavior and the psychological mechanisms that underlie it. But we also hope to demonstrate the considerable power of Darwin's theory. For any question about living thingsfrom the sensory abilities of moths to the complexities of human cognitionan approach that neglects evolution is unlikely to produce full and satisfying answers. Charles Darwin explained the fundamental logic at the core of all living things. If we wish to understand our own, our friend's, our mate's, or our children's behavior, we would be foolish to ignore the insights afforded by an evolutionary perspective.
As will be obvious from our citations and bibliography, we are not the first to imagine the outlines of an evolutionary psychology. Many students of human behavior, not only from the field of psychology but also from biology, anthropology, economics, and the other social sciences, have contributed to the emergence of this field. Our primary debt, then, is to these colleagues, who had both the vision to foresee a synthesis between the evolutionary and behavioral sciences and the interdisciplinary knowledge to build it. We hope that we have portrayed your pioneering efforts as clearly as you would have and that many others will be encouraged to follow you down the Darwinian path.
In particular, we thank our colleagues, Liz Cashdan, Martin Daly, Denys deCatanzaro, Jack Demarest, Jennifer Higa-King, Bruce MacDonald, Janet Mann, B. Kent Parker, Kenneth Wildman, David Sloan Wilson, Matthew Winslow, and Thomas Zentall, who offered frank, thorough, and genuinely useful criticisms of parts, or in some cases all, of the book manuscript. You were (nearly) always right, and we have done our best to implement the various improvements you suggested while keeping in mind the kind of book we wanted to produce.
Thanks also to the following reviewers: Charles Crawford, Simon Fraser University; Sue Koger, Willamette University; Maria G. Janicki, Simon Fraser University; J. Anderson Thomson, Jr., M.D., University of Virginia Student Health Center; Marvin W. Lee, Shenandoah University; and Roger Mellgren, University of Texas at Arlington.
Indispensable editorial and organizational advice and support was generously provided by Cynthia and Claire Gaulin, and Cordelia Stearns. Deborah Fenster, Frances Russello, Sharon Cosgrove, and especially our editor, Bill Webber. We thank you all; it was a pleasure working with you.
We also thank our editor, Jayme Heffler, and production editor, Marianne Hutchinson for their advice, encouragement, cheerfulness, competence, and hard work.
Steven J. C. Gaulin
Donald H. McBurney