- In a word, they became civilized.
一句话 他们变得文明了 - But the only energy at their disposal was provided by nature...
但是他们唯一可以支配的能量来源于自然 - And the strength of their bodies.
以及他们身体的力量 - It was the story of humankind for thousands of years.
这是几千年来人类一成不变的经历 - It still is for one person in four-
这仍旧是世界上四分之一的人类 - Over one and a half billion human beings-
也就是超过15亿人类的经历 - More than the combined population of all the wealthy nations.
这一数字超过了所有富裕国家的人口总和