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Nature allows a seeming excess because the difficulties of life restrict survival of both young and old，and the result of this delicate balance is that populations rise and fall in small numbers; only rarely do they rise to disastrous millions or fall to complete zero. Both plants and animals may reach ages where there they are no longer able to reproduce, butusually before old age is reached sickness, storm, and slowed reactions to danger will have eliminated many individuals. Even a few strong and mature individuals die from disease or under the attacks of a predator.
大自然允許一種表面上的過量，因為生命的艱難竭制了幼小的和年老的生命的存活，這一微妙平衡的結果是，各物種數量上下浮動得很小，只偶爾才成百萬地上升，造成災難，或降跌至零。動植物都能活到不能再繁殖的年齡，但往往等不到年老，疾病、 暴風雨以及對危險的遲緩反應就已經使許多個體的生命消亡。甚至少數強壯成熟的個體生命也會死于疾病或食肉動物的襲擊。
Life is the moving，ever-aggressive force. When any form of life dies，certain life processes take over and act out the saying "waste not，want not" Every atom and molecule of a livin plant or animal was molded by life into a form that is a certain species of life. Those very elements and compounds are needed to continue life, and nature is fairly efficient in recycling them.
生命是一種運動發展、永遠進取的力量。任何一種生命形式消亡時，某種生命過程便會取而代之，實踐起那句"不浪費，不會缺"的老話。活的動植物的每一個分子、原子都是經由生命塑造成某種生命物種形式的。那些元素和化合物正是延續生命所需要的，大自然卓有成效地將它們循環使用。
The controlling factor of life is really "supply and demand". A grass eating animal cannot exist without grass, a predator without prey, a plant without certain basic chemicals or certain kinds of soil. When prey species are rare，the population of predators declines; and when plants lack certain soil，chemical and weather conditions, they decline. Theoretically we would need only to replace those few chemicals filtered out of the soils by water and windsif each of our farm crops were plowed back under the ground, but then we wouldn't have any life-sustaining crops to eat. To raise our crops we need to fertilize by returning chemicals to the soil. It is part of life: through death and decomposing, nature keeps wildlife going.
生命的控制因素實際上是"供求關系"。食草動物沒有草不能生存。食肉動物沒有獵物不能存活，植物沒有某些基本的化學物質或某種土壤不能生長。獵物稀少時，食肉動物的數量就減少；植物缺少一定的土壤、化學物質和氣候條件就會凋零。從理論上來講，如果我們把全部莊稼都犁入土中作肥料，那么我們只需再補上極少數由于水和風而從土壤中流失的化學物質就行了，但那樣的話，我們就不會有賴以生存的糧食了。要種植莊稼，我們得向土壤施加化學物質，使土壤肥沃。大自然通過死亡和腐爛使得野生生物生生不已，這是生命的一部分。
