Picture the antelope being attacked by the lion, but escaping to live another day. Its endorphin would allow the animal to cope with the pain of its wound, if only temporarily, and continue with the herd. Other hormones enable the kidney to retain more water than normal during periods of drought and dehydration.
All of these varied measures are short-term responses to very different types of stress, but they act in a concerted way to give an organism a fighting chance to get back on its feet.
Imagining the types of stress our paleolithic forebears must have encountered makes our daily aggravations seem much less overwhelming. Prior to the advent of agriculture, the typical cave-dweller would rarely have had the luxury of a steady and nutritious diet. On the contrary, malnutrition, vitamin and mineral deficiencies, even starvation would have been extremely common in the winter months, and sporadic dehydration from lack of clean or available water may have been common in the summer.
Hypothermia was a constant threat in the winter, especially in northern climes during the many ice ages. Injuries and infections that resulted from untreated minor wounds or parasite invasion would not only have been physiologically stressful but often lethal. Anthropological data suggest that our ancestors suffered many of the same maladies that continue to plague us today (arthritis, back problems, tooth decay, osteoporosis, to name a few).
However, as stressful as those conditions are for modern man, they would have been far more stressful at a time when no medical treatment of any kind was available.
What about the other type of stress that is not life-threatening, but is perceived to be of potential danger? When the antelope spotted the lion, there was not yet physical damage to the antelope's body. Nonetheless, the hormonal systems responded as if the damage was already done, in anticipation of impending doom. If the crisis were luckily averted, a complex system of hormonal feedback loops would apply a brake on the stress response to prevent unabated secretion of cortisol and other stress hormones.
Our prehistoric ancestors did not need to negotiate city traffic and deal with short-tempered bosses, but they had their share of psychological stress that produced no actual physical bodily insult.
Not knowing when (or if) your next meal will come would have been (and for much of the world's population continues to be) a chronic source of anxiety. Each empty-handed trip back to the cave would have increased the tribe's fears for the next day.
For that matter, obtaining a meal might have meant coping with the terror of chasing down a herd of animals much faster and larger than oneself, using a puny flint arrowhead tied to a stick.
Prehistoric man also differed in one profound way from modern man. Although an awareness of the cycles of nature and physical principles like gravity would likely have been present in even our most primitive ancestors, an understanding of the forces of nature would have completely eluded them.
Having no understanding of science meant having no sense of control over one's environment. Ancient man appears to have worried endlessly about celestial "beings" (sun gods, moon gods, etc.), and we know that until relatively recent times it was common for people to assign human traits to these deities.
This would have implied that it was within the realm of possibility for, say, the sun god to feel angry or neglected one day, thus deciding not to rise and plunging the world into darkness and chaos. Imagine going to sleep each night fretting that you may have failed to properly perform a certain worshipful ritual and that as a consequence your entire tribe or family might be forever doomed to darkness and misery.
From both a physical and a psychological vantage point, our ancestors lived a much more stressful existence than we do today. The mechanisms that evolved to combat the deleterious effects of those stressors are still intact and usually serve us well.
However, we clearly make things worse for ourselves. Take compulsive exercisers. These people can actually become addicted to strenuous exercise, because this behavior imposes a severe stress on metabolism and results in the steady release of endorphin. Responsible for "runner's high," this pain-killer is similar to morphine in its addictive capabilities.
Extreme exercise also releases cortisol, which though useful in maintaining circulatory and respiratory function, can lead to immunosuppression, bone loss, hypertension, and death of brain cells. In yet another scenario, meeting a deadline at work is a source of pressure, but is not life-threatening, and yet it contributes to ill health by invoking an unnecessary release of stress hormones.
Are we stressed in today's society? Of course we are. But the important thing to remember is that all animals, including ourselves, are confronted with innumerable types of stress and always have been. We should ignore the incessant mantra of ours being the Age of Stress and put things in a more historical and evolutionary perspective.
Given the choice, who wouldn't prefer the aggravation of two working parents getting their kids off to day care or school on time to the dread of being eaten in one's sleep by a lion?
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