We can begin our discussion of "population as a global issue" with what most persons mean when theydiscuss "the population problem": too many people on earth and a too rapid increase in the number added eachyear. The facts are not in dispute. It was quite right to employ the analogy that likened demographic(人口统计学的） growth to "a long, thin power fuse that burns steadily and haltingly until it finally reaches the charge, andexplodes".
　　To understand the current situation, which is characterized by rapid increases in population, it is necessary tounderstand the history of population trends. Rapid growth is a comparatively recent phenomenon. Looking back atthe 8,000 years of demographic history, we find that populations have been virtually stable or growing very slightly for most of human history. For most of our ancestors, life was hard, often nasty, and very short. There washigh fertility in most places, but this was usually balanced by high mortality. For most of human history, it wasseldom the case that one in ten persons would have past forty, where infancy and childhood were especially riskyperiods. Often, societies were in clear danger of extinction because death rates could exceed their birth rates. Thus, the population problem throughout most of history was how to prevent extinction of the human race.
　　This pattern is important to know. Not only does it put the current problems of demographic growth into a historical perspective, but it suggests that the cause of rapid increase in population in recent years is not asudden enthusiasm for more children, but an improvement in the conditions that traditionally have caused high mortality.
　　Demographic history can be divided into two major periods: a time of long, slow growth which extended fromabout 8000 B.C. till approximately 1650 A.D. and a period of rapid, dramatic growth since 1650. In the first periodof some 9,600 years, the population increased from some 8 million to 500 million in 1650. Between 1650 and thepresent, the population has increased from 500 million to more than 4 billion. And it is estimated that by the year2020 there will be 8 billion people throughout the word. One way to appreciate this dramatic difference in suchabstract numbers is to reduce the time frame to something that is more manageable. Between 8000 B.C. and 1650,an average of only 50,000 persons was being added annually to the world's population each year. At present, thisnumber is added every six hours. The increase is about 80,000,000 persons annually.