The Biology of Human Survival: Life and Death in Extreme Environments CLAUDE A. PIANTADOSI, M.D. OXFORD UNIVERSITY PRESS The Biology of Human Survival This page intentionally left blank The BIOLOGY of HUMAN SURVIVAL Life and Death in Extreme Environments CLAUDE A. PIANTADOSI, M.D. Center for Hyperbaric Medicine and Environmental Physiology Duke University Medical Center Durham, North Carolina 1 2003 3 Oxford New York Auckland Bangkok Buenos Aires Cape Town Chennai Dar es Salaam Delhi Hong Kong Istanbul Karachi Kolkata Kuala Lumpur Madrid Melbourne Mexico City Mumbai Nairobi São Paulo Shanghai Taipei Tokyo Toronto Copyright © 2003 by Oxford University Press, Inc. Published by Oxford University Press, Inc. 198 Madison Avenue, New York, New York, 10016 www.oup-usa.org Oxford is a registered trademark of Oxford University Press All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of Oxford University Press. Library of Congress Cataloging-in-Publication Data Piantadosi, Claude A. The biology of human survival : life and death in extreme environments / Claude A. Piantadosi. p. cm. Includes bibliographical references and index: ISBN 0-19-516501-2 1. Extreme environments. 2. Adaptation (Biology) 3. Human physiology. I. Title. QP82.P536 2003 612—dc21 2003040497 987654321 Printed in the United States of America on acid-free paper Adapt or perish, now as ever, is nature’s inexorable imperative. —H.G. Wells This page intentionally left blank To persevere across far-ranging environments is profoundly human, but life at the extremes is constrained in extraordinary ways. The diversity of environments in which people are found, either as permanent inhabitants or as temporary visi- tors, ranges from the high Andes to the scorched Sahara to the frigid Arctic, yet these places are a small fraction of those that harbor life in the thin biosphere around the planet’s surface. Most of Earth is too inhospitable for even optimally adapted individuals, and out of necessity, curiosity, or self-indulgence, we have invented technologies to venture into previously impenetrable domains, from the depths of the oceans to the depths of space. Humans on the frontiers of exploration are tested to the limits of their lives. The Biology of Human Survival pinpoints critical factors that dictate life or death at the utmost reaches, including those places accessible to humans only with life- support technology. The book presents environmental physiology using modern, integrated concepts of stress, tolerance, and adaptation. Barriers to life in extreme environments, such as dehydration, starvation, and radiation, are described in separate chapters. Other chapters explain the problems unique to specific envi- ronments by examining the determinants of an individual’s survival at extremes of cold, heat, altitude, or immersion. Key issues in these specialized settings are illustrated with examples of extreme hardship from great exploits that have at- tracted people’s attention throughout history. Preface For each environment the book asks these central questions: How does the human body respond to the change in environment and what happens when adap- tive mechanisms fail? When does biology reach its limits and when must technol- ogy take over? How do scientists evaluate the biological responses to extreme states and solve life-support problems under such conditions? These intriguing ques- tions and their implications offer a fresh look at the human condition. The book reveals the intricacy with which the human body responds and adapts to environmental change and reminds us that physics and biology collide head- on at many levels, which leads to multiple stresses and numerous opportunities to counter them. As implied by the common etymology of the words physics and physiology, it is physics that limits life. The physics needed to understand these limitations is explained in language that will be meaningful to students of biology at all levels. Despite the great heterogeneity of environmental stimuli, all stresses evoke cer- tain common responses. These have been organized in the book to unify general survival principles with mechanisms of adaptation to specific environments. The overarching principles are the body’s recognition of stress and the brain’s control of physiological systems in order to optimize cardiovascular, respiratory, renal, and hormonal performance. These adjustments conserve and manage vital body resources, such as water, salt, and heat and provide time for the individual to escape or for the body’s molecular machinery to adapt. Probing common reactions to different stresses also provides an opportunity to point out unique stress responses and ingenious solutions to living in mar- ginal environments found throughout the animal kingdom. This allows one to better appreciate why specific functions must be supported in specific environ- ments by man-made devices. Accordingly, the biology in this book is appropri- ate for engineers and physical scientists as well as any intelligent explorer of the natural world. The struggle between organism and environment is nature’s paradigm, but this is often underplayed in human endeavors. We consider ourselves separate from other animals because we adapt to new environments, in part, by rational action. Thus, the book’s underlying theme is the role of behavior in adaptation, empha- sizing circumstances in which human technology will forever change the envi- ronment, such as after a nuclear war or during colonization of space. Once the subtle interplay of environment with the body’s responses and the individual’s behavior is grasped, a new window opens onto human survival. The distinction between biology and behavior is somewhat artificial but con- ceptually useful. Behavioral adaptation as embodied in modern technology has eliminated most of the day-to-day pressures that molded our ancestors. Virtually instantaneous access to resources such as food, water, shelter, power, medicine, and transportation shape today’s individual as much or more than does biologica1 adaptation. The long-term implications of this shift in our way of life are not well viii PREFACE understood, and the book describes special environments, such as long voyages in space, in which these unknowns may become especially important. That environment shapes humanity is never at issue in the book. Rather, we, more than any other species, stand to influence our destiny through our ability to alter the natural world. The natural consequences of global environmental change are familiar to all biologists, and ecological change that creates hardships over which many individuals cannot prevail and multiply will extinguish whole species. A famous example is the effect of the insecticide DDT on the loss of durability of the eggshell of predatory birds, such as the bald eagle (Carson, 1963). Overuse of DDT after World War II threatened their extinction by interfering with the birth- rate of hatchlings, a problem that went uncorrected until long after DDT was banned in the United States. Our propensity to restructure our environment and, soon, our own biology has fantastic implications for human survival that are touched on in the book. This topic has caused theorists to argue over the process of human evolution; some have even proclaimed its end. In any event, modifying the environment at the expense of biological adaptability alters humanity’s evolutionary direction. A fore- warning of what may await us lies in the fossil record of extinctions brought about by radical fluctuations in climate, but whether change in our environment or our biology is the more significant factor remains unknown. These matters of “population biology” raise the issue of whether information about our own biology can help us avoid extinction. Human intelligence brings optimism to this prospect, but great cleverness is a double-edged sword that car- ries the specter of self-annihilation. It is also true that knowledge of human biol- ogy is progressing faster than is natural biology itself, but no matter how pleasing the vision of mind over nature, it underestimates natural selection and the effect of the unpredictable on human evolution. The debate over human evolution is beyond the scope of the book, which deals with the individual, for whom the outcome of environmental stress can be reduced to tolerance and adaptation or death. These outcomes, however, have important ramifications for the long-term survival of humans both on this planet and else- where in the solar system. Thus, understanding how individuals adapt to the en- vironment is a step on the road to discovering how the physical world shapes human biology. Durham, North Carolina C.A.P. Preface ix [...]... on human biology, and learning where these limits are and how to deal with them is what biologists call limit physiology The principles of limit physiology can be applied to understanding human life in all extreme environments These principles will be developed in this chapter and applied throughout the book to gain a deeper appreciation of how humans survive in extreme conditions The Nature of Human. .. conditions, the greater the engineering requirements and the higher the cost In considering life- support equipment, three distinct but related environments are always involved: the internal environment of the body, the environment adjacent to the body, and the external environment, that is, the environment outside the suit or system By first principles, the objective is to maintain the internal stability and. .. set point and the reference value and generates an error signal that initiates a compensatory response The intensity of the error signal determines the intensity of the compensatory response This is the gain in the system The gain determines how rapidly the parameter returns toward the set point, thus completing a feedback loop As the actual value of the parameter approaches the set point, the error... advantage in some environments but not in others The ultimate extreme environment, that of space, is used to point out gaps in our knowledge of long-term human endurance and adaptation outside the confines of Earth Throughout the book common determinants of survival in artificial environments are highlighted as much as possible, together with their implications for the future of humankind 2 Survival and. .. to allow the organism to function properly amid the varying influences of the external environment Integration is the key principle in understanding how the human body functions The Science of Human Physiology The study of how a living organism functions normally despite disturbances in the environment is the discipline of physiology Because all living systems attempt to maintain constant internal... O2 in the blood (hypoxic hypoxia), lack of 12 THE BIOLOGY OF HUMAN SURVIVAL Figure 2.1 The major physiological functions of the body Five major organ systems of the body are shown in the framework of the pulmonary and circulatory systems The table indicates the main functions and the percentage of basal metabolism (BMR) necessary to support function Overall metabolism increases and the distribution of. .. for the concept of homeostasis, paid tribute to Bernard’s milieuintérieur in the development of his own ideas In the preface to the French edition of his book The Wisdom of the Body, Cannon acknowledged that its main tenet, that the stability of the inner medium of the organism is actively regulated in higher vertebrates, was “directly inspired by the precise view and deep understanding of the eminent... is 1 in 1000, and the probability of death (Pd) if one event occurs is 1:100 The probability of death for each event is therefore the product of P × Pd, or 1 in 100,000 The probability of both events occurring is the product of their probabilities, or 1 in 1 million, but if both occur the probability of death is (set at) 1.0 (certainty) Therefore, the overall risk of death is the sum of the three products,... function will decline to the point that the accumulation of urea and other metabolites will interfere with brain function and result in the coma of uremia The problem of rising blood urea could be viewed as a change in the set point for the clearance of urea by the kidneys However, this view of the system begs the question because if something intervenes to reverse the hypertension, recovery of kidney function... and intensity of the stress or strain Adaptation shifts the position of the curve to the right The Human Environment 3 port highly sophisticated and unique forms of life, but the thought of people existing permanently in such places is unimaginable Many species that thrive in the depths die when brought too quickly to the ocean’s surface Of the land that covers the remaining third of the Earth’s surface, . The Biology of Human Survival: Life and Death in Extreme Environments CLAUDE A. PIANTADOSI, M.D. OXFORD UNIVERSITY PRESS The Biology of Human Survival This page intentionally left blank The BIOLOGY of HUMAN SURVIVAL Life. depths of the oceans to the depths of space. Humans on the frontiers of exploration are tested to the limits of their lives. The Biology of Human Survival pinpoints critical factors that dictate life. understanding human life in all extreme environments. These principles will be developed in this chapter and applied throughout the book to gain a deeper appreciation of how humans survive in extreme