Environmental Problems, Their Causes, and Sustainability 1

Extremely EffectiveTotal abstinenceSterilizationVaginal ringHighly EffectiveIUD with slow-releasehormonesIUD plus spermicideVaginal pouch(“female condom”)IUDCondom (good brand)plus spermicideOral contraceptive100%99.6%98–99%98%98%97%95%95%93%smaller number of children because fewer children dieat an early age.Average age at marriage (or, more precisely, the averageage at which women have their first child) alsoplays a role. Women normally have fewer childrenwhen their average age at marriage is 25 or older.Birth rates and TFRs are also affected by the availabilityof legal abortions. Each year about 190 millionwomen become pregnant. The United Nations and theWorld Bank estimate that about 46 million of thesewomen get abortions: 26 million of them legal and20 million illegal (and often unsafe).The availability of reliable birth control methods (Figure10-12) allows women to control the number andspacing of the children they have. Religious beliefs, traditions,and cultural norms also play a role. In some countries,these factors favor large families and strongly opposeabortion and some forms of birth control.EffectiveCervical capCondom (good brand)Diaphragm plusspermicideRhythm method (Billings,Sympto-Thermal)Vaginal sponge impregnatedwith spermicideSpermicide (foam)Moderately EffectiveSpermicide (creams,jellies, suppositories)Rhythm method (dailytemperature readings)WithdrawalCondom (cheap brand)UnreliableDoucheChance (no method)10%40%75%74%74%70%86%84%83%82%89%84%Figure 10-12 Typical effectiveness rates of birth control methodsin the United States. Percentages are based on the numberof undesired pregnancies per 100 couples using a specificmethod as their sole form of birth control for a year. For example,an effectiveness rating of 93% for oral contraceptivesmeans that for every 100 women using the pill regularly for ayear, 7 will get pregnant. Effectiveness rates tend to be lower indeveloping countries, primarily because of lack of education.Globally about 39% of the world’s people using contraceptionrely on sterilization (32% of females and 7% of males), followedby IUDs (22%), the pill (14%), and male condoms (7%). Preferencesin the United States are female sterilization (26%), the pill(25%), male condoms (19%), and male sterilization (10%).(Data from Alan Guttmacher Institute, Henry J. Kaiser FamilyFoundation, and the United Nations Population Division)What Factors Affect Death Rates? ReducingDeathsDeath rates have declined because of increased foodsupplies, better nutrition, advances in medicine, improvedsanitation, and safer water supplies.The rapid growth of the world’s population over thepast 100 years was not caused by a rise in the crudebirth rate. Instead, it was caused largely by a decline incrude death rates, especially in developing countries.More people started living longer and fewer infantsdied because of increased food supplies and distribution,better nutrition, medical advances such asvaccines and antibiotics, improved sanitation, andsafer water supplies (which curtailed the spread ofmany infectious diseases).Two useful indicators of overall health of peoplein a country or region are life expectancy (the averagenumber of years a newborn infant can expect to live)and the infant mortality rate (the number of babies outof every 1,000 born who die before their first birthday).Great news. The global life expectancy at birth increasedfrom 48 years to 67 years (76 years in developedcountries and 65 years in developing countries)between 1955 and 2004. It is projected to reach 74 indeveloping countries by 2050. Between 1900 and 2004,life expectancy in the United States increased from 47to 77 years and is projected to reach 82 years by 2050.Bad news. In the world’s poorest and least developedcountries, mainly in Africa, life expectancy is 49years or less. In many African countries life expectancyis expected to fall further because of more deaths fromAIDS.Infant mortality is viewed as the best single measureof a society’s quality of life because it reflects acountry’s general level of nutrition and health care. Ahigh infant mortality rate usually indicates insufficientfood (undernutrition), poor nutrition (malnutrition),182 CHAPTER 10 Applying Population Ecology: The Human Population