Stress is a major pathway through which psychosocial factors affect physiology and the aging process. Cannon was the first physiologist to systematically describe the physiological effects of stress. Selye expanded on cannon"s conceptions in two ways. Selye said there are three stages in reaction to stress. The second stage is adaptation where there is a return to physiological homeostasis and the third stage is exhaustion where the organism may fall ill or die if the stress continues. Modern conceptions of the stress response differ in several important ways. Cannon and seyle argued that there are general responses to stress, but it is now widely recognized that there are individual differences in stress reactions. There is an individual response in heart rate, respiratory rate, and galvanic skin response. Researches have been so focused on the negative consequences of stress that possible positive outcomes tend to be overlooked. Those with stress matured more quickly than their non-stressed peers.