Population Growth, Resource Consumption, and The Environment 5–7.Key Determinants of Population Growth 4–5.Most of this growth will take place in developing countries. We face the prospect of a further doubling of the population within the next half century. The lag between downward shifts of death and birth rates may be many decades or even several generations, and during these periods population growth will continue inexorably. The rate at which the demographic transition progresses worldwide will determine the ultimate level of the human population. The shift from high to low death and birth rates has been called the “demographic transition.” These successes have led to a slowing of the world's rate of population increase. Some have already achieved family sizes small enough, if maintained, to result eventually in a halt to population growth. Over the last 30 years, many regions of the world have also dramatically reduced birth rates. Success in reducing death rates is attributable to several factors: increases in food production and distribution, improvements in public health (water and sanitation) and in medical technology (vaccines and antibiotics), along with gains in education and standards of living within many developing nations. This accelerated population growth resulted from rapidly lowered death rates (particularly infant and child mortality rates), combined with sustained high birth rates. Within less than the span of a single lifetime, it has more than doubled to 5.5 billion in 1993. This number grew to 100 million people about 2,000 years ago and to 2.5 billion by 1950. It took hundreds of thousands of years for our species to reach a population level of 10 million, only 10,000 years ago. He world is in the midst of an unprecedented expansion of human numbers.
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