Tonight, I want use a quote from the book to point to a common problem with any kind of social change -- unintended consequences. Social systems, especially when one gets to the level of nations and world civilizations, are very complex. Even very small changes in one part of a social system can have significant consequences throughout the entire system; not all of which can be anticipated. Even when they can be anticipated by some, calls for caution are not always heeded.
Brown writes about the very real problem of over-population. The human population of earth, now more than 6 billion, and growing, has by many calculations already exceeded the carrying capacity of the earth's biosphere. (See Meadows, Randers and Meadows Limits to Growth 2004 and Mathis Wackernagel 2002 study published by the U.S. National Academy of Sciences). Bringing population growth under control is certainly necessary for preserving civilization.
Brown writes about an intrinsic benefit of rapid reduction in birth rate:
…[help] countries that want to slow their population growth to do so quickly. This brings with it what economists call the demographic bonus. When countries move quickly to smaller families, growth in the number of young dependents—those who need nurturing and educating—declines relative to the number of working adults. In this situation, productivity surges, savings and investment climb, and economic growth accelerates.
Japan, which cut its population growth in half between 1951 and 1958, was one of the first countries to benefit from the demographic bonus….This effect lasts for only a few decades, but it is usually enough to launch a country into the modern era.
(http://www.earth-policy.org/Books/PB3/pb3ch7.pdf pages 149-150)
While the "demographic bonus" is real, and has the consequences described above, it is disingenuous not to also acknowledge the unintended consequences and problems produced by rapid reduction of birthrate 50 years later.
Japan is one of the best examples of the unintended consequences. Japan epitomizes the future problems that will be faced by all nations that make this demographic shift, especially those that make it quickly. This is the problem of a rapidly aging population, where those over 65 are becoming a larger and larger percentage of the Japanese population. The burden of caring for and paying for the needs of an aging population is becoming apparent throughout the developed nations, but it is particular acute in Japan, because that nation's demographic transition was so sudden, so abrupt. The flip side of having a smaller number of young dependents compared to the working adult population, in the decades immediately following the demographic transition, is inexorably followed fifty years later by having a much larger number of elderly dependents compared to the working population.
One could argue that a rapid decline in birthrates and demographic shift provides the potential for 50 years of economic growth that will make dealing with a large elderly population easier. But it is necessary for people invoking the need for a decline in birth rates to acknowledge the future consequences of these changes. Nation's making significant demographic transitions need to have full knowledge of the long term consequences and begin planning for those now.