Young rats that are handled by humans will develop larger adrenal glands, but nonetheless as adults will show a more muted stress response to threats. They also tend to live longer, one study finding a life expectancy 18 percent longer than that of nonstressed rats. The acute stressors must, however, be acute and moderate, for the same research showed that major stressors early in life, such as maternal separation, foster an anxious adult ill prepared to deal with the slings and arrows of normal life events. The training or toughening effects of acute intermittent stress can also be observed
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