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THE WORLD'S EXPLODING POPULATION KARL SAX* More than one hundred and fifty years ago Thomas Malthus, English clergyman and social economist, proposed his laws ofpopulation growth. According to Malthus, all organisms, both plant and animal, tend to increase in numbers faster than do the means ofsubsistence, and population growthmust be controlled eitherby "positive checks" whichresult inhigh death rates or by "preventive checks" which result in low birth rates. He concluded that "the race ofplants and the race ofanimals shrink under this great restrictive law, and man cannot by any efforts of reason escape from it." Among the positive checks to the growth ofhuman populations Malthus includes "exposure to the elements, extreme poverty, disease, epidemics , war, plague and famine." He concluded that "the preventive check, so far as it is voluntary, is peculiar to man, and arises from that distinctive superiority of his reasoning faculties which enables him to calculate distant consequences." Malthus, like all clergymen of his time, did not approve of artificial birth control, andhehadlittle faith in whathe called "prudential restraint" in married life as a means ofreducing the birth rate. Nor did he believe that the "passion between sexes" would decline in future generations. Thus he concluded that the excessive growth of human populations must be controlled by high death rates resulting from poverty, disease, starvation, and war. Malthus could not foresee the great advances in science and technology which permitted a fivefold increase in the population of England since 1800, accompanied by a great advance in the standard ofliving. Nor did * Emeritus Professor of Botany, Harvard University. Address: Bishop Hollow Road, Media, Pennsylvania. TWs paper was presented as a Sigma Xi lecture at twenty-two colleges and research centers in March, 1962. It was rejected for publication in the Sigma Xijournal, The American Scientist. 32I he realize that the leaders ofhis church would eventually approve ofcontraception . But his basic law ofpopulation growth is as valid today as it was 150 years ago; the growth ofhuman populations must be controlled by high death rates or by low birth rates. During most ofhuman history population growth was controlled by high death rates. With little protection from the elements, with no control of disease, with uncertain and often inadequate food supplies, and with constant strife and warfare, early man led a very precarious life. Before the advent of agriculture the human population grew very slowly. The average annual rate of growth could not have exceeded about 0.02 per cent—a rate that would require about three thousand years for the population to double in number. Before the advent ofagriculture the world population could not have exceeded 20 million, according to Sir Arthur Keith, and may have been much less [1]. With the development ofagriculture, starting about 8000 B.c., human survival was greatly enhanced. But productive agriculture was limited to the flood plains ofthe great rivers because at that time man did not have the tools needed to cultivate the forested areas and the prairie grasslands. Population growth must have varied greatly during this period ofearly agriculture, but the average annual growth rate from about 8000 B.c. to A.D. ? probably did not exceed 0.04 per cent—a rate that would require about 1,500 years for the population to double. By the beginning of the Christian Era the world population was about 250 million. The next sixteen centuries were little better for human survival. It was about 1650 before the world population reached 500 million, having doubled in about 1,600 years. By 1820 the world population was about ? billion, having doubled in 200 years. In 1930 the population was about 2 billion, having doubled in 100 years. The world's population reached 3 billion in 1961, and at the present rate ofgrowth ofabout 2 per cent per year it will exceed 6 billion by the end of this century, doubling in less than 40 years. But this is far from the maximum rate. Several countries are growing at the rate of more than 3.5 per cent annually, a rate that would double the population in about 20 years. This recent explosive growth of the human population is due almost entirely to reduction of...


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