The Biology of
Human Survival:
Life and Death in
Extreme Environments
CLAUDE A. PIANTADOSI, M.D.
OXFORD UNIVERSITY PRESS
The Biology of Human Survival
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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
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Kuala Lumpur Madrid Melbourne Mexico City Mumbai
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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

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

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

The body’s minimum daily water requirements, 45
The mechanism of dehydration and the body’s responses, 47
Dehydration and heat tolerance, 49
Survival time without drinking water, 51
6. Water That Makes Men Mad, 54
The composition of seawater, 55
Ingestion of seawater, 55
Survival at sea, 56
Lessons from the USS Indianapolis, 57
A practical approach to salt and water loss at sea, 60
7. Tolerance to Heat, 63
Mammalian homeothermy, 63
Humans as tropical primates, 64
Body heat balance, 65
Heat acclimatization, 70
Heat acclimatization and physical fitness, 71
The limitations of human tolerance to heat, 72
Heat illnesses, 73
Death by heatstroke, 76
8. Endless Oceans of Sand, 78
The camel and the Berber, 79
Desert lessons from Pablo and the Haj, 83
Thermal stress and behavior, 84
Importance and regulation of heat-escape activities, 86
9. Hypothermia, 89
The effects of extreme cold on the extremities, 89
Settings for systemic hypothermia, 90
The physiology of hypothermia, 92
Unexpected effects of cold and hypothermia, 95
The subtle effect of winter on human mortality, 96

The physics of submarine disasters, 156
Analysis of survival factors on sunken submarines, 158
15. Climbing Higher, 164
The physical environment of high altitude, 164
Physiological responses to high altitude, 166
High-altitude illnesses, 173
The zone of death, 176
Limits of human ascent to high altitude, 179
16. Into the Wild Blue Yonder, 181
The International Standard Atmosphere, 181
Human visitation to the stratosphere, 183
Depressurization accidents, 185
xiv CONTENTS
The Armstrong line, 188
The pressure suit, 189
17. G Whiz, 193
The continuity principle, 193
Gravity and acceleration, 194
High-G environments, 195
Limits of high-G tolerance, 197
Adaptation to sustained G forces, 201
18. The Gravity of Microgravity, 203
Space sickness, 204
Intolerance of upright posture, 204
Loss of bone mass in space, 206
Loss of muscle mass in space, 209
19. Weapons of Mass Destruction, 212
Biological and chemical warfare agents, 213
Thermonuclear weapons, 217
Types of radiation, 219

maintain an active equilibrium, however brief or delicate, with its natural envi-
ronment. All living beings, as integral parts of nature, can be characterized by the
dynamic exchange they maintain with their physical surroundings. Being alive
requires being attuned to natural change, and many organisms are exquisitely
2 THE BIOLOGY OF HUMAN SURVIVAL
sensitive to even tiny perturbations in environmental conditions. They occupy
restricted niches. If changes in conditions in the niche exceed certain limits, bio-
logical equilibrium is disrupted, and the life of the organism, or even the entire
species, is threatened. Thus, all habitable environments, or habitats, have specific
physical boundaries within which life is possible and outside which life is impos-
sible. As an organism approaches the limits of its habitat, life is sustainable only
with greater and greater effort unless the effort is sufficient for adaptation to occur.
Indeed, the closer the organism approaches a tolerance limit, and the greater the
stress, the more vigorous will be the attempt to compensate, and if it falls short,
the shorter will be the survival time. This principle is illustrated in Figure 1.1. The
curve has the shape of a rectangular hyperbola, which is characteristic of many
survival functions depicted throughout this book.
Human beings are among the most adaptable creatures on the planet, yet the lim-
its of human survival are astonishingly narrow when viewed in the context of the
extremes on the planet. Approximately two-thirds of the Earth’s surface is covered
by deep saltwater oceans, which air-breathing terrestrial mammals such as ourselves
may visit briefly but are not free to inhabit. Even highly specialized diving mam-
mals, the great cetaceans, so spectacularly adapted for life in the sea, are confined
to the surface layers of the ocean. The crushing pressure of the seawater, the cold,
and the darkness make the great depths of the ocean inhospitable to most marine
species. Not that life cannot exist or even thrive under such extremes, for even at
the bottom of the sea super-hot water jets heated by vents in the Earth’s mantle sup-
Figure 1.1. The relationship between the ability to compensate for and the severity of
physiological stress or strain. X-axis indicates time to failure of function, or, in the case of
survival, to death. The time scale may be in any unit, from seconds to days, depending on

of advanced behavioral adaptation.
4 THE BIOLOGY OF HUMAN SURVIVAL
endure the most grueling conditions, surviving prolonged immersion, high alti-
tude, and heat or cold despite desperate thirst or impending starvation. The in-
credible tales of survival at sea, in the mountains, in the desert, and on the ice
capture our imaginations like few others.
The Importance of Preparation for Extreme Exposures
Every life-and-death struggle is influenced by intangibles, sometimes lumped
under broad terms such as survival instinct and will to live. Whether an individual
survives an unexpected and prolonged encounter with a potentially lethal envi-
ronment, however, depends more on the equilibrium between biology and phys-
ics than on intangibles. Although much has been made of a strong will to live,
this is a basic trait of the human psyche common to healthy people. Strength of
spirit, motivation, and psychological factors are very important for survival but
are less decisive under truly catastrophic conditions than our poets and writers
would like us to believe. To state it plainly, rarely does one person survive under
extreme conditions when another dies simply because the survivor has a greater
will to live.
Thoughtful preparation in anticipation of extreme exposure is more important
than all the fighting spirit in the world, for a naked man cannot live out a night at
the South Pole. Preparation, however, requires knowledge, time, and resources.
It involves allowing time to adapt, for example by gradual ascent to an altitude or
by arranging resources to limit the effects of the exposure, such as by providing
multiple layers of warm, dry clothing on polar expeditions. Preparation when an
automobile breaks down in the desert means simply avoiding death from dehy-
dration by having had enough foresight to carry along some water. This example
implies the double failure that has killed many a bold explorer. One failure oc-
curs before the adventure begins by counting on a single vehicle and not carrying
enough water to walk out or to survive until another vehicle can come to the res-
cue. The second failure, engine trouble, usually nothing more than an inconve-

d
, 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, or 2.1 in 100,000. The bottom part of the
diagram shows two independent events, a and b, arranged in a linear system in which a
has already occurred but has no consequences because it occurs before b in a different
environment or location, for example, before an exposure. However, if the exposure is
undertaken and b then occurs, the probability of death increases from 1 in 100 to 1.0 (cer-
tainty) because a is already in place. Therefore, failure to account for a fixes the probabil-
ity of death at 1 in 1000, which is nearly fiftyfold higher than in the top part of the diagram.
Examples are provided in the text.
6 THE BIOLOGY OF HUMAN SURVIVAL
A good example is ejecting from a burning jet aircraft with a defective explo-
sive canopy bolt. If an independent probability of 1:1000 is assigned to each
event, the probability of experiencing the double failure is 1:1000 squared, or
only one in a million. The chances of living through it however, are virtually
zero. Overall, the expected probability of death in this linear system is
2.1:100,000.
Next, consider the problem of starting an expedition with a failure already in
place. This is illustrated in the bottom half of Figure 1.3. In the desert example
above, the motorist left town without a supply of drinking water. In this case, the
event, a, is assigned a probability of 1 because it happened, but it did not happen
in the desert and the motorist can find water anytime before departure. The prob-
ability of dying of dehydration is nil. The second failure, b in Figure 1.3, has a
probability of 1:1000, but now the probability of death is 1. This means the over-
all risk of dying on the expedition has gone from 2.1:100,000 to 1:1000, nearly a
fiftyfold increase. These calculations give one an appreciation for why most of
the deaths in mountaineering, deep sea diving, parachuting, and so on are due to
double failures that involve at least one human error. The initial failure often en-

accounting of four factors, which can be defined as critical variables. The first
two variables are beyond human control, while the latter two are amenable to
intervention. These critical variables are as follows: (1) the physics of the envi-
ronment, (2) the limits of human physiology, (3) the length of the exposure, and
(4) behavioral adaptation, including what the victim understands about survival
requirements and the plans made to prepare for a failure.
This approach simplifies the analysis, but not greatly because the four critical
variables are complex. In other words, they are true variables, neither constants nor
necessarily simple changes, and this makes survival prediction an inexact science.
For instance, hostile environments do not produce “pure” physiological stresses;
many places are both hot and dry, such as the Sahara, or cold and high, such as the
Antarctic. This results in multiple stresses on the body that interact with one an-
other. To further complicate the situation, human biology encompasses differences
in body shape, mass, and fitness that greatly influence survival time under different
conditions. This aspect of the problem, known as physical diversity, is most obvi-
ous for survival in cold water. Physical diversity implies that certain body charac-
teristics, such as, fatness, carry different degrees of importance under different
conditions, such as providing temporary advantage while immersed in cold water.
Figure 1.4. Survival probability in a parallel system. In this diagram events a and b are
arranged in parallel. In other words, if a occurs, option b can be exercised to prevent death
because of a, and vice versa. Thus, double failures, a and b, must occur to cause death.
The risk of death during the exposure is greatly reduced, from 1 in 1000 to 1 in 1 million,
by the redundancy. Examples are provided in the text.
8 THE BIOLOGY OF HUMAN SURVIVAL
As a general rule, the order in which the factors are listed above is their order
of importance, even if parameters within each factor change. On the other hand,
when a potentially lethal exposure is in the offing, the fourth factor, behavioral
adaptation made by interventions by victim and rescuer, is the only means of pro-
ducing a survivor. The principle also holds when one prepares for extreme expo-
sure known to exceed one of the body’s physiological limits. The only effective

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 stabil-
ity and functions of the body, which means that the critical environment is imme-