Environmental Problems, Their Causes, and Sustainability 1

topic on the website for this chapter. Such an optimumlevel would allow most people to live in reasonablecomfort and freedom without impairing the ability ofthe planet to sustain future generations.What is the optimum population size for the world(or for a particular country)? No one knows. Some considerit a meaningless concept; some put it at 20 billion,others at 8 billion, and others as low as 2 billion.Those who do not believe the earth is overpopulatedpoint out that the average life span of the world’s6.4 billion people is longer today than at any time in thepast and is projected to get longer. They say that theworld can support billions more people. They also seemore people as the most valuable resource for solvingthe problems we face and stimulating economic growthby becoming consumers.Some believe that all people should be free to haveas many children as they want. And some view anyform of population regulation as a violation of their religiousbeliefs. Others see it as an intrusion into theirprivacy and personal freedom. Some developing countriesand some members of minorities in developedcountries regard population control as a form of genocideto keep their numbers and power from rising.Proponents of slowing and eventually stoppingpopulation growth have a different view. They pointout that we fail to provide the basic necessities for oneout of six people on the earth today. If we cannot orwill not do this now, they ask, how will we be able todo this for the projected 2.5 billion more people by2050?Proponents of slowing population growth warnof two serious consequences if we do not sharplylower birth rates. One possibility is a higher death ratebecause of declining health and environmental conditionsin some areas—something that is alreadyhappening in parts of Africa. Another is increased resourceuse and environmental harm as more consumersincrease their already large ecological footprintin developed countries and in developing countriessuch as China and India that are undergoing rapideconomic growth.Population increase and the consumption thatgoes with it can increase environmental stresses suchas infectious disease, biodiversity losses, loss of tropicalforests, fisheries depletion, increasing water scarcity, pollutionof the seas, and climate change.Proponents of this view recognize that populationgrowth is not the only cause of these problems. Butthey argue that adding several hundred million morepeople in developed countries and several billionmore in developing countries can only intensify existingenvironmental and social problems.These analysts believe people should have thefreedom to produce as many children as they want,but only if it does not reduce the quality of other people’slives now and in the future, either by impairingthe earth’s ability to sustain life or by causing socialdisruption. They point out that limiting the freedom ofindividuals to do anything they want, in order to protectthe freedom of other individuals, is the basis ofmost laws in modern societies.xHOW WOULD YOU VOTE? Should the population of thecountry where you live be stabilized as soon as possible?Cast your vote online at http://biology.brookscole.com/miller14.How Can Economic Development HelpReduce Birth Rates? Economics Worked Once,But Will It Work Again?History indicates that as countries becomeeconomically developed, their birth and deathrates decline.Demographers have examined the birth and deathrates of western European countries that industrializedduring the 19th century. From these data they developeda hypothesis of population change known asthe demographic transition: as countries become industrialized,first their death rates and then their birthrates decline.According to this hypothesis, the transition takesplace in four stages (Figure 10-20):First is the preindustrial stage, when there is littlepopulation growth because harsh living conditionslead to both a high birth rate (to compensate for highinfant mortality) and a high death rate.Next is the transitional stage, when industrializationbegins, food production rises, and health care improves.Death rates drop and birth rates remain high,so the population grows rapidly (typically 2.5–3% ayear).During the third phase, called the industrial stage,the birth rate drops and eventually approachesthe death rate as industrialization, medical advances,and modernization become widespread. Populationgrowth continues, but at a slower and perhaps fluctuatingrate, depending on economic conditions. Mostdeveloped countries and a few developing countriesare in this third stage.The last phase is the postindustrial stage, when thebirth rate declines further, equaling the death rate andreaching zero population growth. Then the birth ratefalls below the death rate and population size decreasesslowly. Forty countries containing about 14%of the world’s population have entered this stage andmore of the world’s developed countries are expectedto enter this phase by 2050.188 CHAPTER 10 Applying Population Ecology: The Human Population