Walter Cannon and Hans Selye used animal studies to establish the earliest scientific basis for the study of stress. They measured the physiological responses of animals to external pressures, such as heat and cold, prolonged restraint, and surgical procedures, then extrapolated from these studies to human beings.
Subsequent studies of stress in humans by Richard Rahe and others established the view that stress is caused by distinct, measureable life stressors, and further, that these life stressors can be ranked by the median degree of stress they produce (leading to the Holmes and Rahe Stress Scale). Thus, stress was traditionally conceptualized to be a result of external insults beyond the control of those experiencing the stress. More recently, however, it has been argued that external circumstances do not have any intrinsic capacity to produce stress, but instead their effect is mediated by the individual’s perceptions, capacities, and understanding.