This model was called GENERAL ADAPTATION SYNDROME [GAS].
Hans Selye proposed the three stages model of GAS, the three stages are alarm, resistance and exhaustion. During the alarm stage, the sympathetic nervous system prepares the body for action. In the resistance stage, the sympathetic nervous system recruits resources that will be needed to maintain high level of activity and energy. In the exhaustion stage,the parasympathetic nervous system takes over and the body experiences physical illnesses.
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They got used to it or invented something that made it easier to live in that environment
