问答题The Earth is full! Four billion people have crammed into every desirable and fruitful area and have spilled over into all the barren and inhospitable areas. Under the pressure of the fullness, the wilderness is disappearing, competing plants and animals are dying out; the weather is changing and the soil is failing. And yet there is perhaps an even more fundamental danger to humanity in the Earth’s fullness than is represented by any sort of physical deterioration. Humanity began as a thin cluster of primitive hominids in East Africa about four million years ago. About two million years ago, the first hominids appeared who were sufficiently close in structure to the human being to be placed into genus Homo. It was not until 150,000 years ago that the hominids brain developed to a size sufficient to produce the first organisms we can classify as Homo sapiens, and it was only 50,000 years ago that “modem man,” Homo sapiens, made his appearance on the Earth. His increase in range was slow indeed. It was not till 30,000 years ago that human beings began to enter Australia and the American continents, and even as late as 300 years ago, those continents were but thinly occupied. Then came the Industrial Revolution and the Earth filled with what was, on the evolutionary scale, an explosion. In a couple of centuries, the world population quintupled from 0.8 billion to 4.2 billion, and now Earth bears all the human load it can manage and, in many places, somewhat more than it can manage. Consider, then, that we and our hominid ancestors evolved on an essentially empty Earth. There was always the possibility, during times of stress, that one might pick up as much of one’s belongings as one could carry and travel to the other side of the hill， where conditions might be better, where a new life might be built and where a new chance might be taken.【Key words】 hominid类人动物， 原始人 genus Homo 人属； 人类 Homo Sapiens智人（现代人的学名）

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