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Living systems tend to maintain in equilibrium variables associated with their continued existence. Environ mental conditions which force these variables beyond their normal ranges produce stress within the system. Feedback mechanisms then seek to restore equilibrium. Stress arises from overloads or underloads of energy and information, as well as from inputs which have threatening implications. The process of adapting to stress depends partly on the nature of the stress-producing agent and partly on the mechanisms available to the system. Exposure to heat, for example, involves dilation of blood vessels, reduction of body activity, and sweating to reduce body heat. At the same time, the system undergoes neurophysiological and endocrine changes which are found in many other types of stress. When the system is subjected to extreme environmental conditions for an extended period of time, adaptive responses may become increasingly costly. A possible outcome is one of the "dis eases of adaptation" described by Selye. Eventually, adap tive mechanisms may fail and the system may collapse. The stress encountered by most individuals arises from the symbolic, rather than the physical, aspects of their environ ment. Among the exceptions are groups such as antarctic explorers, mountain-climbers, prisoners of war, and crews of space vehicles. Although problems arise under these condi tions, most studies of men under stress reveal a remarkable capacity for adaptation to extreme environments.

A systems approach to the process of adaptation to extreme environmental conditions is presented, utilizing the concepts input, output, & adaptation. The process of adaptation to extreme conditions produces a 'general adaptation syndrome,' characterized by stress-producing inputs, or stressors, of energy or information. The readjustments involved in adapting to stressful inputs may be complex. They include both specific changes determined by the nature of the environmental conditions & nonspecific responses of the system to emergencies. Nonspecific adjustments in humans range from the alerting response, which signals an alteration in the environment, to widespread changes involving multiple subsystems. These can be divided into 3 interrelated categories: (a) responses mediated by the reticular system; (b) those mediated by the sympathetic division of the autonomic nervous system; & (c) those mediated by the pituitary-adrenal system. Coping mechanisms for information overloads, whether in a cell, an individual, a small group, a large org or society include the following categories: ommission; queuing; filtering; multiple channels; approximation; error; & escape. When stress arises from the meaning of information inputs, the following major patterns of adjustment to symbolic dangers are possible: repression; denial; rationalization; reaction formation; undoing; isolation; projection; regression; & displacement. Although the environmental changes which threaten our society may soon constitute energy inputs which require adaptive adjustments, most people are now confronted with extreme environments in a symbolic rather than a realistic sense. No matter how extreme the environment, examples can usually be found of compensatory processes which have enabled most individuals to adapt. 1 Figure. M. Maxfield.