A proposed classification of environmental adaptation: the example of high altitude

摘要

Extreme environments are defined as the opposite of usual environments where the evoked physiological responses are unperceiv-able,repeatable and adjusted to the constraint. Adaptation strategies to a given environment show three levels: cultural or technological,where a buffer space is built to protect the organism from the hostile milieu,physiological,where temporary adaptive mechanisms are developed,and genetic,where full adaptation is possible with normal life and reproduction. The cost of adaptation increases from the genetic level (minimal cost) to the technological level. These concepts are illustrated by the example of adaptation to altitude hypoxia. The technological level is given by the use of oxygen bottles by high altitude climbers. The physiological level involves various physiological and biological systems (increase in heart rate,ventilation,erythropoiesis,expression of hypoxia-inducible factors,etc.). The genetic level has been reached by some animal species such as Yaks,Llamas,Pikas but has not yet been demonstrated in humans. Diseases developed during exposure to acute or chronic hypoxia may be considered as "adaptive crises" that mimic the transition to a lower energy level of adaptation.