Living with the earth gary moore

HUMAN POPULATION - Moore

LIVING WITH THE EARTH

CHAPTER 2

HUMAN POPULATION

HUMAN POPULATION - Moore

Objectives for this Chapter

A student reading this chapter will be able to:

1. Define the attributes of populations including birth and death rates, growth rate, density, and mobility (immigration and emigration).

2. Calculate rate of natural increase from birth and death rates, and mathematically demonstrate the effects of age-sex composition on a population.

HUMAN POPULATION - Moore

Objectives for this Chapter

3. Define biotic potential and maximum growth rate, and list the various limits to growth

4. Identify, list, and explain the population growth forms.

5. Recognize and explain the concept of population explosion with respect to complete and incomplete demographic transition. Define population implosion and discuss the conditions that lead to this phenomena.

HUMAN POPULATION - Moore

Objectives for this Chapter

6. Explain the role of urbanization in influencing sustainability of populations.

7. Explain global population projections and differentiate between developed and lesser developed countries with respect to those projections.

8. List and discuss the various options for fertility control methods, while contrasting the effectiveness, risks, and benefits of each type.

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LIVING WITH THE EARTH

HUMAN POPULATION

INTRODUCTION

Understanding the dynamics of human populations is a first order of business in beginning the study of environmental health.

There is growing realization that surging populations, environmental degradation, and ethnic conflict are strongly intertwined.

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LESSER DEVELOPED COUNTRIES

Overpopulation, infectious disease, unprovoked crime, few resources, and the influx of more refugees, increases the erosion of nation-states leading to the empowerment of private armies, security firms and international drug cartels.

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LESSER DEVELOPED COUNTRIES

This is a vision of the early 21st century in many parts of the lesser developed countries (LDCs), and threatens to expand along with the growth of human populations.

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THE CHARACTERISTICS OF POPULATIONS

Species

A species is normally considered to be a group of organisms that can breed together with the production of a viable and fertile offspring.

Different species not only have differing physical attributes, but they also differ in the population characteristics.

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Population

A population is considered to be the breeding group for an organism.

Each population has characteristics that help to identify it.

Some of these characteristics are birth rate, death rate, rate of natural increase, age distribution, and sex ratio.

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Birth Rate

Birth rate refers to the number of individuals added to a population through reproduction (live births) and is normally expressed as the number of live births per 1,000 population (counting the population at the midpoint of the year)(Fig. 2-1).

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Death Rate

Death rate is also similarly calculated using total deaths divided by the mid-year total population (Fig. 2-1).

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Rate of Natural Increase

The rate of natural increase is determined by subtracting the death rate from the birth rate (Fig. 2-1).

The rate of natural increase reflects the growth rate in which migration is not considered.

The growth of a population in the absence of migration must depend on the birth rate being higher than the death rate.

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Fig. 2-1

Birth rate equals the number of live children born in a year per 1 000 total population

Birth rate in year Y = Number of live children born in year Y over the midyear population in year Y

Birth rate in year 1998= 4,345,600 (children born in 1998) over 271,600,000 (population in mid-1998)= 16/1000

Death rate in year y= 2,172,800 (deaths in 1998) over 271,600,000 (population in mid-1998) = 8/1000

Rate of natural increase in year 1998 = (Birth rate - Death rate) = 811000 or 0.8 percent*

*These are approximate numbers for the United States used only for example.

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Age Distribution

The age-sex composition of the population has a profound effect on the birth and death rates of a country because the probability of dying or giving birth within any given year depends upon the age and sex of the population members Fig. 2-2.

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Age Distribution (Fig. 2-2)

Graph showing the age distribution in different regions. The reproductive ages are noted as 15-50, which has the most people in stable and declining populations. Expanding populations have more children under 14 than any other ages

Expanding populations: Mexico, Asia, and Africa have a bell curve distribution between relationship of percentage of population and age, with 7% of the population being under the age of 14 and 2-3% over the age of 55.

The United States is a stable population with a much steeper, more jagged bell curve with people over 55 making up 3% of the population and children making about 3.5% of the population

Western Europe and Japan are declining populations with an even steeper curve, with only 3% children and 1-2% adults over 55

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THE CHARACTERISTICS OF POPULATIONS

Total Fertility Rates

Total fertility rates(TFR) represent the number of children a woman in a given population is likely to bear during her reproductive lifetime providing that birth rates remain constant for at least a generation.

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THE CHARACTERISTICS OF POPULATIONS

Immigration

In nature, when the density of organisms becomes too great, the intense competition for food, water, and other resources damages the entire population. Some species have the ability to disperse or migrate out of the area and in doing so, temporarily relieve the overcrowding.

This process is called emigration.

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Immigration

When species emigrate from an area, they must immigrate or enter into another area.

Driven by natural disasters, war, disease, and disappearing resources, the numbers of refugees worldwide may exceed 15 million, with about 880,000 to 1.4 million immigrants entering the United States each year, including more than 200,000 who enter illegally.

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POPULATIONS DYNAMICS

There are periodic upsurges in many populations that lead to overwhelming numbers.

Whether these population explosions occur in rabbits, lemmings, soldier ants, or locusts, there is always some natural pressures that bring the population back into balance with their natural surroundings.

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POPULATIONS DYNAMICS

Biotic Potential

The unrestricted growth of populations resulting in the maximum growth rate for a particular population is called its biotic potential.

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POPULATIONS DYNAMICS

The biotic potential of species differs markedly and is influenced by: (1) the frequency of reproduction; (2) the total number of times the organism reproduces; (3) the number of offspring from each reproductive cycle; and (4) the age at which reproduction starts.

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POPULATIONS DYNAMICS

Environmental Resistance

Environmental resistance refers to those pressures that limit population and may include such factors as disease, wars, predatory behavior, toxic waste accumulation, or species competition (Fig. 2-3).

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Fig 2-3

Biotic potential – environmental resistance = actual rate of resistance.

Graph with population on y axis and time on x axis

Environmental resistance is food, light, or space shortage, climate changes, disease, predatory behavior, toxic wastes, competition

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POPULATIONS DYNAMICS

By plating bacteria as outlined in figure 2-4, one can examine and then plot a bacterial growth curve (Fig. 2-5).

Lag Phase

The initial part of the curve in which the organisms show no increase in growth rate, but are preparing for the exponential growth phase which follows.

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Fig. 2-4

Original inoculum is diverted into various test tubes, one to another, so it loses potency.

The first tube creates too many confluent colonies to count on a nutrient agar plate, the next creates less, the third less than that, and the final creates 2x10 to the sixth power colonies/ml

Calculation: Number of colonies on plate x reciprocal of dilution of sample= bacteria/ml. In this example, there are 20 colonies on the plate of 1:100,000 dilution = 2 million bacteria/ml. A growth curve can be constructed if the original inoculum is counted by this process hourly for 24 to 48 hours.

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Fig. 2-5

Graph with time up to 24 hours on the x axis and log of numbers of bacteria on the y axis. An S curve shoes the lag phase for the first 6 hours, the log or exponential growth phase for the next six hours, the stationary phase for six hours after that and the death or logarithmic decline phase for the remaining 12 hours

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Fig. 2-6

If an organism grows too rapidly and the population escalates beyond the carrying capacity of the environment in which it is located, a “J” type growth curve may develop (Fig. 2-6).

X axis is time and y axis is log of numbers of organisms. A short lag phase is followed by a steep log or exponential growth phase which exceeds carrying capacity

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POPULATIONS DYNAMICS

This behavior sometimes oscillates every few years as in the case of lemmings that inhabit the arctic tundra north of the Canadian forest.

Every 3 to 4 years the population explodes, then crashes the following year, followed by a 2 year cycle of slow recovery (Fig 2-7).

Figure 2.8 shows the effects of predators on populations.

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Fig. 2-7

Graphic depiction of lemming population cycles. Every 3 to 4 years the population explodes, then crashes the following year, followed by a 2 year cycle of slow recovery.

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Fig. 2-8

Population size cycles but is relatively constant. This can be effected by the presence of predators. Graphic shows a squiggly but relatively constant rate of population for animals’ population size, then the same population over time in the presence of a predator, with a pronounced decline.

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POPULATIONS DYNAMICS

k-Strategy (type I”)

When large organisms with relatively long life spans have only a few offspring, but devote their energies to protecting and nurturing the offspring to enhance their individual survival until they can reproduce (Fig.2-9).

Density dependent factors include such items as food supply, which becomes more limiting as the size of the population grows.

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POPULATIONS DYNAMICS

r-Strategy

r-strategy populations are typically small, short-lived organisms, which produce large numbers of offspring and receive little or no parental care (Fig. 2-9).

These organisms are limited by density-independent factors such as a drought that dries up a pond, or sudden climactic changes such as El nino which alters the temperature of the water making it uninhabitable for certain species.

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Fig. 2-9

Adapted from Turk & Turk. 7

Graph of r-strategy, Type II and k strategy/type I populations with number of survivors on the y axis and age on the x axis. R-strategy populations are Type III: insects, fungi, fish, mollusks, plants. They produce large numbers of offspring and receive little or no parental care. They don’t live long. K-strategy organisms with relatively long life spans have only a few offspring, but devote their energies to protecting and nurturing the offspring to enhance their individual survival until they can reproduce. Type II populations are some birds, and humans experiencing malnutrition and disease.

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POPULATION TRENDS IN THE WORLD

Demographers use the information on population size, fertility rates, migration, birth and death rates, growth rates, infant mortality, density, age-sex composition and other factors to statistically characterize human populations.

Their purpose is to predict what will happen to that population over time.

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POPULATION TRENDS IN THE WORLD

Historical Trends

After earth’s temperature stabilized about 10,000 years ago, humans began to domesticate animals and cultivate crops, this allowed the human population to increase (Fig. 2-10).

Since then, the world growth rate has increased dramatically, although we are currently experiencing a downward trend (Fig 2.11).

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Fig. 2-10

Adapted from Turk & Turk. 7

Graph with population in billions on the y axis ranging from 0 to 6 and year on the x axis. Ranging from 2 million BC to 1998. 2 million BC to 0 BC is considered to be before the Christian era. Once the Christian era began, population began to steadily increase and spiked in 1998, when it reached 6 billion.

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Fig. 2-11

Graph showing thesteady increase in the annual rate on natural population increase in the world from 1700 to modern times. There was a spike in population in 1970, with a 2.06% increase and slow decline to a 1.4% increase in 1997.

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Historical Trends

Growth Rate

The rate of births is the ratio of births to the population, and death rates represent the ratio of deaths to the population.

Growth rate is then determined by the birth rate minus the death rate.

The population has grown so much, that even the smaller growth rates lead to additions of larger numbers of people to the global population (Fig 2-12).

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Fig. 2-12

Graph of population growth from 1960-2000. Year is depicted on the x axis. Annual increase in world population from 0-90 million on the y axis. Even smaller growth rates lead to additions of larger numbers of people to the global population, growing 1.7% in 1960 lead to 51 million more people and a total population of 3 billion, whereas growing 1.4% between 1998-2000 lead to 85 million more people and a total population of 6 billion.

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Historical Trends

Doubling Time

Another useful way to demonstrate growth rate is to present it as doubling time (Fig. 2-13), or the number of years for a human population to double its size. The doubling time can be calculated according to the following relationship:

doubling time = 0.70 / growth rate

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Fig. 2-13

Doubling time in years from 0 to 700 on the y axis, countries and regions on the x axis. Northern Europe has taken 700 years to double at 0.1 %- the rate of natural increase. Southern Europe has taken 350 years to increase .2%, Western Europe has taken 233 to increase .3%, U.S, 87.5 to grow .8%, Oceania 53.8 to grow 1.3%, Asia 50 to grow 1.4%, South America 46.6 to grow 1.5%, and Africa 26.9 years to grow 2.6%

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Historical Trends

Demographic Transition

Developed countries have exhibited slowly declining birth and death rates over the last century.

This has resulted in a diminishing difference between birth rates and death rates and a very low rate of natural increase resulting in a stable population with very long doubling times (Fig. 2-14).

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Fig. 2-14

Adapted from United nations Population Fund. 3

DeBirth rate vs. death rate in more developed countries between 1750-2000. Slowly declining birth and death rates have resulted in a low rate of natural increase. Birth rate = 11/1000

Death rate = 10/1000. 11-10=0.1 rate of natural increase and a doubling time of 700 years

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Historical Trends

Incomplete Demographic Transition

LDCs do not have the resources to institute social security, and have unstable policies that fail to capture the trust of its citizens.

The populations had remained stable with high birth rates and high death rates.

Developed countries introduced better sanitation and nutrition to LDCs, resulting in a decrease of the death rate (Fig. 2-15).

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Fig. 2-15

Adapted from United nations Population Fund. 3

Less developed countries have high birth rates and newly lower death rates, with a high rate of natural increase. Birth rate = 31/1000. Death rate = 10/1000. 31 – 10= 2.1 rate of natural increase. Doubling time = 33 years.

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Current Population Trends

The world’s population is growing at a rate of 1.4 percent annually and is expected to reach six billion people by the middle of 1999

Almost 98 percent of the annual increase in the world’s population is occurring in the LDCs.

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Population Decreases in the Developed Countries

Declines in Fertility

In 1970 there were 19 countries reporting declining fertility rates while in 1997 over 57 countries have reported below-replacement fertility rates.

By the year 2060, Europe will have lost almost 25 percent of its population.

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Population Decreases in the Developed Countries

Concerns About Decline

There is a concern throughout Europe and Japan that the declining population will result in decreasing house and land prices as the demand declines along with the population.

In the southern island of Kyushu, Japan, officials are offering a gift of $5,000 to parents who have a fourth or subsequent child.

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Population Decreases in the Developed Countries

Concerns About Decline

Higher education for women with new aspirations and higher incomes, is considered to be a factor for declining fertility rates in many countries.

In fact, as illiteracy among women decreases in a country, the average number of children born to those women declines (Fig. 2-16).

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Fig. 2-16

The greater the level of illiteracy among women, the more children they are likely to have. The more money a woman earns in the home, the fewer children she is likely to have.

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Population Decreases in the Developed Countries

Fertility Rates in the United States

The replacement TFR level for most countries is accepted as being 2.1.

Subtle changes in social attitude appeared to produce rather significant changes in fertility rates (Fig. 2-17).

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Fig. 2-17

Source: U.S. Bureau of the Census

Total fertility rate on y axis between 0 and 4.0. X axis has the years between 1920-1997. The replacement TFR is 2.1. The US has spent more than 20 years at below replacement level.

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Population Decreases in the Developed Countries

Immigration and the Changing Racial Landscape in the United States

Although the TFR has remained below replacement levels, immigration adds at least another 850,000 to 1.2 million people to the United States each year.

The expanding population of elderly white will be expecting support from a working population of tremendous diversity and proportionally fewer workers per retiree (Fig. 2-18).

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Fig. 2-18

In 1950 there were 16.5 workers per retiree. In 1997 there were 3.3 workers per retiree/ By 2025 there will only be 2.2 workers per retiree.

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Current Population Trends in the Less Developed Countries

More than 80 percent of the world lives in the LDCs.

In the next 20 years 1.76 billion children will be born in the LDCs (Fig. 2-19).

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Fig. 2-19

Adapted from Population reference Bureau 2 and the United Nations Population Fund.3

Population in a bar graph showing contrast between developed and lesser developed countries from 1750 to 2100. Developed countries have a significantly slower population growth. By 2100, 2 billion people will live in developed countries and 12 billion in lesser developed countries.

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Predicted Future Trends in Populations

The median or best estimate by the United Nations is that the world population will stabilize at 11.5 billion people around the year 2150 if the world fertility rate drops to 2.06 and life expectancy is 85 years (Fig.2-20).

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Fig. 2-20

Adapted from Doyle18 and Motavallui.19

Projections of population growth. With a TFR of 2.5 there will be 28 billion people in 2150. With a TFR of 2.06 there will be 11.5 billion. With a TFR of 1.7 there will be 4 billion in 2150.

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Urbanization - What is it?

The mass migration of people to the cities.

Megacities

Defined as having a population of more than 10 million, will be commonplace by the year 2015, with 9 of the 10 largest cities being in the the developing countries. (Figs.2-21, 22).

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Fig. 2-21

Adapted from the Environment.17

Bar graph of urbanization across the globe, will Tokyo being the only city in a developed country that houses much of the population at about 30 million, Bombay India has roughly the same amount. Lagos Nigeria and Shanghai China have about 22 million. Jakarta Indonesia has just over 20 million, Sao Paulo Brazil and Karachi Pakistan have about 20 million Beijing China, Dhaka Bangladesh, and Mexico City Mexico have about 18-19 million.

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Fig. 2-22. Borders of W. Africa merged by megacities

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Urbanization

Facilitates the spread of disease.

Potential increase in violence

Environmental degradation

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THE CONTROL OF POPULATION

Empowerment or Force

Countries attempting to bring population growth under control without first empowering women and providing effective birth control have often resorted to oppressive population control policies.

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Population Policies in Some Countries

India

India was the first country to introduce family planning in 1951, with the rhythm method.

China

China continues to enforce a one-child policy in the nation’s largest cities such as Beijing and Shanghai.

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Family Planning Versus Population Control

Population Control

Government directed programs that set a policy for establishing an optimum population size.

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Family Planning Versus Population Control

Family planning

Population control is in contrast to family planning programs that are directed at assisting couples in having the number of children they desire regardless of how many.

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METHODS OF FERTILITY CONTROL

Introduction

Methods that prevent fertilization of the egg are called contraception.

Methods vary in their risks to health, their efficacy in preventing pregnancies, ease of use, acceptance, and costs.

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Contraceptive Methods that are Reversible

Natural Birth Control and Family Planning

Hormonal

Oral Contraceptives (Fig. 2-23)

Depo-Provera

Norplant (Fig. 2-24)

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Fig. 2-23

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Fig 2-24

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Contraceptive Methods that are Reversible

Spermicides (Fig. 2-25)

Barrier Methods

Male Condom (Fig.2-26)

Female Condom (Fig. 2-27), Diaphragms, and Cervical Caps (Fig. 2-28)

Intrauterine Devices (IUD’s) (Fig. 2-29)

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Fig. 2-25

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Fig. 2-26

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Fig. 2-27

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Fig. 2-28

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Fig. 2-29

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Contraceptive Methods that are Permanent

Sterilization has become one of the most popular methods for contraception in the United States among married couples who have achieved their desired level of parenthood

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Contraceptive Methods that are Permanent

Vasectomy

Male sterilization by making an incision on either side of the scrotum and snipping out a piece of the vas deferens.

Tubal Ligation

Blocks the entry of eggs into uterus, eggs released from the ovaries dissolve and are reabsorbed into the body.

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Contraceptive Methods that are Permanent

Abortion

The medical means of terminating a pregnancy.

Nearly 60 million abortions occur annually on a worldwide basis.

Abortion can also be safely induced within the first 9 weeks of pregnancy by administering the drug RU-486.