Biological approach psychologyWatch
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Just quoting in Puddles the Monkey so she can move the thread if needed
I guess you could say that the stress responses activates the body for activity. For example, the hypothalamic-pituitary-adrenal axis (hormonal response) stimulates the release of corticosteroids which can have the effect of increasing blood glucose levels, thus increasing availablity of glucose for respiration for energy. Equally the sympathetic-adreno-medullary pathway (Nervous system response) leads to the release of adrenaline, which activates the sympathetic nervous system- thus increasing heart rate and basically leading to the fight or flight response- muscle tension, vasodilation, increasing breathing rate etc.
Therefore you could say stress is evolutionary because stress may occur in times of danger (say being chased by a lion), and the components of the stress response such as the release of adrenaline prepare the body for activity- either to fight the stressor or run from it.
Hope that helps a bit