adaptation, physiologicalchange in the reaction that organisms show as a result of prolonged exposure to conditions that normally produce a different or more extensive reaction. For example, mountain sickness (headache, nausea, fatigue) in a human being passes off as he or she becomes acclimatized to high altitudes because of adjustments that occur in the respiratory and circulatory systems. See ACCLIMATIZATION.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005