DNA and Destiny: Nature and Nurture in Human Behavior PDF
Preview DNA and Destiny: Nature and Nurture in Human Behavior
R. Grant Steen DNA and destiny Nature and nurture in human behavior DNA and Destiny Nature and Nurture in Human Behavior DNA and Destiny Nature and Nurture in Human Behavior R. GRANT STEEN Springer Science+Business Media, LLC Library of Congress Cataloging-in-Publication Data On file ISBN 978-0-306-45260-4 ISBN 978-1-4899-2768-2 (eBook) DOI 10.1007/978-1-4899-2768-2 © 1996 R. Grant Steen Origina11y published by Plenum Press in 1996. 10 9 8 7 6 5 4 3 2 1 All rights reserved No part of this book rnay be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher Be patient toward all that is unresolved in your heart and try to love the questions themselves.-Rainer Maria Rilke Acknowledgments My wife, Wil O'Loughlin, has been a wonderful partner during the draining process of writing, and she and my children, Alena and Mariei, have provided love, light, warmth, and laughter, as well as a healthy dose of perspective. My parents, Noreen and Ralph Steen, have been supportive and enthusiastic throughout the process of c1arifying confusion, identifying ignorance, and delimiting real knowledge. Colleagues at the University of California, Los Angeles, have played a large role in teaching me to think like a scientist while writing like aperson: Dr. Leonard Muscatine still serves as a model of c1arity in writing; Dr. George Laties is an example of the etemal youth of the questioning mind; and Dr. Margaret McFall-Ngai remains one of the best scientists I know. I also want to thank Matthew Galvez and Dr. Linda Porter, who encouraged me to follow this path; Dr. Barry Fletcher and Dr. June Taylor, who make it possible to continue; and Linda Regan and Jeanne Fredericks, who have helped it all to happen. v Contents Chapter 1 Genes and Human Behavior 1 Chapter 2 The Old Nature versus Nurture Debate 21 Chapter 3 The Dark History of Eugenies 33 Chapter 4 The Nature of Nurture: Defining Environmental Influences 49 Chapter 5 New Tools for an Old Problem 63 Chapter 6 New Improvements in the Old Tools 79 Chapter 7 The Inheritance of Disease: A Paradigm for the Inheritance of Behavior? 93 Chapter 8 Intelligence 113 Chapter 9 Mental Disorders 137 Chapter 10 Personality Traits 161 Chapter 11 Sexual Orientation 185 Chapter 12 A1coholism and Addictive Behavior 203 Chapter 13 Crime and Violence 217 Chapter 14 Sex, Genes, and Testosterone 239 Chapter 15 Biology and Sodal Responsibility 261 Epilogue 279 References 283 Index 293 vii 1 Genes and Human Behavior Animal breeders, who bred and selected for loyalty in dogs, or speed in horses, or docility in cattle, were probably the first to notice the powerful influence of heredity, even if they didn't know the word or understand the principles. Certainly all successful breeders realized that much could be known about the traits of a newborn animal by having a thorough familiarity with the bloodlines of that animal. The bloodlines of racing horses in England have been recorded in the Stud Book for more than 200 years. The impetus for keeping this record for so many years is the sure knowledge that a cross between two slow horses will virtuaHy never produce a fast horse. This simple perception is an affirmation that, to at least some extent, DNA is destiny. The first Stud Book, published in 1793, listed almost 200 horses available for sire, but only 3 of those horses have had offspring through all of the intervening years. Thus, every thoroughbred racing horse in the world today can trace its ancestry back to one of these 3 horses. Yet, even though the bloodline of each racing horse in the world is known, in some cases back for more than 20 generations, breeding a faster racehorse remains somewhat a matter of chance. While DNA may decree destiny, the destiny it decrees is apparently not a fixed and immutable one. The medieval preoccupation with the bloodlines of nobility, or the Victorian emphasis on noble breeding as aprerequisite for inclusion in polite society, both may originate from the percep tion that genes can determine the future as weH as the past. 1 2 Chapter 1 Similarly, the current fascination with genealogy may arise from the realization that an above-average ancestor can be a source of good genes, as weH as a source of good cocktail-party conversa tion. And when a modem father asks his daughter if her new boymend "comes from a good family" he is reaHy looking for a rough indication of what the future may bring. Perhaps if the new boymend comes from a long line of intelligent, weH-balanced, and successful forebears, he will not turn out to be the axe-murderer he resembles. The first recorded experiment designed to test the question of whether nature or nurture is more important in human development occurred in the 13th century. King Frederick 11 of Germany became curious about what kind of language would develop among children reared without any exposure to preex isting language.1 He was curious as to whether children would teach themselves the Hebrew language, which was the oldest language extant in Europe at the time, or one of the more recent languages such as Greek or Latin. Therefore, he ordered foster mothers to rear and care for aseries of children without speaking to them, or exposing them to language in any way. But this experiment was a terrible failure, since aH of the children died fairly quickly. Apparently they could not live without the bonding that is fostered through language. Six centuries later in England, Francis Galton studied the heritability of genius. Galton began by identifying the most celebrated men of his day, men who were famous scientists, authors, judges, musicians, military leaders, clerics, and states men. He then searched the family trees of these men to deter mine whether or not they were related to other eminent men of the past or present. Galton set the most famous person in each family as the referent, and determined the likelihood that one famous person would be related to another by blood. He found that a famous man was far more likely to have a famous son or brother than to have a famous cousin. This implies that what ever qualities made the referent individual famous are likely to be present in near relatives as weH. Galton's study, published in 1869 as a book entitled Hereditary Genius: An Inquiry into its Laws Genes and Human Behavior 3 and Consequences, became very widely read, and it inspired generations of scientists to believe that heredity has much to say about the course of the future. In 1871, Charles Darwin wrote in The Descent of Man that " ... in regard to mental quaIities, their transmission is manifest in our dogs, horses, and other domestic animals. Besides special tastes and habits, general intelligence, courage, bad and good tempers, etc., are certainly transmitted." This was a key observation for Darwin, because it implied that mental and physical qualities both could be selected for by a breeder interested in changing the traits of an animal. It was only one step further from this idea to the idea that nature itself could act as an agent of selection. In fact, Darwin used his observations on the breeding of domesticated animals as one of the central arguments in The Descent of Man, since this was something he and every other Englishman of his day was familiar with. Natural selection and the heritability of traits remain the central tenets of the theory of evolution, since new traits must be inherited for evolution to occur. Darwin's emphasis on the impor tance of heredity in determining both physical and mental traits persuaded generations of scientists to see the invisible hand of genetics at work everywhere, and this bias continues to the present day. The flush of recent successes in molecular biology has focused public attention on that most complex and mysterious of all chemicals, DNA. Every feature of our physical being is coded for by DNA, and many scientists would argue that virtually every aspect of humanity is similarly encoded. The Human Genome Project, which proposes to sequence the entire human complement of DNA, is an acknowledgment that to know the code is, at least in part, to know the bearer of the code. The hype and hard seIl surrounding this project has by now convinced many people that our future is indelibly written in our genes. Scientists have been reluctant to make explicit how large the gap is between knowing the sequence of the human genome and understanding the various ramifications of that sequence. Con sequently, there is now a perception that we are closing in on a molecular understanding of the human condition. And most 4 Chapter 1 people are aware that, though genes can determine good health and above-average intelligence, genes are also responsible for many undesirable traits. There is a growing concern, to the point of consensus, that genes can predict a limited future for certain unfortunate individuals. This fatalism is a recurrent theme of the recent book The Bell Curve, as it makes the argument that dass structure in the United States is largely determined, even defined by intelligence. However, the question of what deter mines intelligence is never adequately dealt with: if nature determines intelligence, then the defeatist theme of the book is perhaps appropriate; but if nurture determines intelligence, then giving up on the disadvantaged will eventually be equivalent to giving up on our society. In asense, this is the dark side of the revolution in our understanding of genetics; a fatalism born of the conviction that one cannot rise above one's genetic station. But this genetic fatalism is an overreaction; molecular biology and molecular genetics may be king, but there are troubles in the kingdom. In fact, molecular biology, evolutionary theory, and chaos theory appear to be somewhat at odds with one another. Molecular biology is concerned, at least in part, with the molecular machin ery of heredity. Two basic tenets of molecular biology are that the function of the whole can be understood completely in terms of the parts, and that the machinery of heredity is very nearly infallible. Molecular biologists thus adhere to a somewhat static world view, in that change is generally not permitted to enter the picture. On the other hand, evolutionary theory is concerned with change and the consequences of inheritance. A basic tenet of evolutionary theory is that the evolution of organisms is inevitable, because the environment is constantly changing and because the machinery of heredity is imperfect. Finally, chaos theory is concerned with discerning the underlying structure of seemingly random objects or events. A basic tenet of chaos theory is that it is essentially impossible to define the whole by studying the parts, because we have an inadequate grasp of the parts and because conditions are changing far too rapidly. Thus,
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