摘要：There was a time in the world's history when physical peril was the greatest threat to man's existence. Those who reached what we now call "middle age" were considered lucky, wise, brave, skillful, and old. They somehow survived frightening tangles with beasts long extinct, healed from broken bones and torn flesh, braved thousands of freezing, dark nights and all the mysterious, unseen dangers it brought, weathered bou ts of famine, and resisted succumbing to hunger, eventual malnutrition, and death. As man's understanding of the world around him increased, so did his chances of survival. Man worked with the elements within his reach. Fire was the first. The night wo uld no longer hold the cold or danger it once did. Earth was next. Man learned to grow edible plants and harvest its fruits. Water followed. Irrigation meant that as much as man needed to feed, he could grow.
