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Resilience and Survival in Extreme Environments 165

system, and modulation of the immune response. Th e individual diff erences
considered by these authors included cortisol responses, heart rate reactivity,
and natural killer cell cytotoxic activity. Kosslyn et al. report the results of
numerous studies detailing how stress and immune responses diff er among
individuals and how these processes are related to both short-term (i.e., acute
illnesses) and long-term (e.g., diseases such as cancer) health. Th ey propose
that as the study of individual differences becomes more refined and is coupled

with advances in genomics, a clearer understanding of psychological and bio-

logical variations will emerge. This will support a more complete understand-
ing of the interaction between psychology and biology, and will ultimately
support an increasingly useful understanding of functions and processes that
are essential to stress resilience.

Conclusions and Recommendations for Future Research

Human physiological limits in extreme environments are largely known and
understood. Less well understood are exceptional adaptations that make some
individuals and populations uniquely capable to perform eff ectively in extreme
environments, and the underlying mechanisms by which behavioral limita-
tions are activated to prevent physiological damage. In some cases, behavioral
limits can be exceeded to the detriment of the human body (e.g., heat stroke
following extreme physical performance in warm environments) but in other
situations, the limiting physiological responses may be maladaptive (e.g.,

impaired decision making in hypothermia). In a description of the fine line we
tread between biological mechanisms that sustain health or produce disease,
the Nobel laureate, Aaron Ciechanover, has observed that “man wants to walk
in the rain but doesn’t want to get wet” (A. Ciechanover, speech in Herzilya,
Israel, 24 October 2006). In unique situations where extraordinary perfor-
mance is required, those who can temporarily push the physiological limits
and still survive are considered resilient. Moderators, which can be used to
expand human behavioral limits within the range of physiological capacity,

are important to our understanding of modifiable resilience. Exercise and fi t-
ness appear to be important in this regard. Physical fitness increases resilience

in extreme environments, promoting improved performance as well as lasting
neuro-protective effects, and this is currently a key research initiative for mil-

itary medical research. Adaptations noted in specific highland populations

indicate a strong genetic influence upon resilience to the effects of altitude.

Current technologies such as proteomics and comprehensive approaches
using systems biology techniques (Hood, Heath, Phelps & Lin, 2004) will help
to explain the underlying mechanisms that provide advantages in various

specific extreme environmental conditions. Other potential moderators such
as meditation and conditioning may be beneficial as strategies to moderate

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