Human Population Chapters 8 and 9
I. The principles of population ecology apply to humans.
A. The world population was 6.07 billion in 2000 and increased by 85 million from 1999 to
2000.
1. Although our numbers continue to increase, the growth rate (r) has declined slightly
over the past several years, from a peak in the mid-1960s of 2.2% per year to
1.4% per year in 2000.
2. Demographers , scientists who study population statistics, project that the world
population will become stationary (r = 0), that is, zero population growth, by
the end of the 21st century.
B. Highly developed countries have the lowest birth rates, lowest infant mortality rates,
longest life expectancies, and highest per-capita GNPs. Developing countries have
the highest birth rates, highest infant mortality rates, shortest life expectancies, and
lowest per-capita GNPS. In recent decades, it has become useful to recognize a
distinction within the developing countries between:
1. Moderately developed countries (e.g., Argentina, Brazil, Chile, Mexico,
Thailand, Turkey, and Venezuela.)
2. Less developed countries or “LDCs” (e.g., Bangladesh, Cambodia, Laos,
Ethiopia, and Niger.)
C. The Demographic Transition refers to a commonly observed sequence of populationrelated events through which populations or nations almost invariably pass during the
course of industrialization:
1. In the preindustrial stage, birth rates and death rates have been in equilibrium for
many generations during which the level of the technology used by a society
remained essentially unchanged. Infant mortality rates are characteristically high
during this stage, and disease is often an important regulator of population as
well.
2. In the transitional stage, technologies which can offer the largest reduction in
human misery in return for the smallest investment of capital are introduced.
These early transitional technologies include public health measures ensuring
access to clean water and reduced human contact with sewage. The great
European plagues were ended not by the developing of modern medicine but
by improvements in public health measures. Vaccinations also offer a lot of
“bang for the buck” and are among the earliest misery-reducing technologies to
be introduced. Birth rates do not begin to decline until late in the transitional
stage, so the imbalance between r and d generates a period of tremendous
population growth.
3. In the industrial stage, the population finally begins to enjoy the benefits of
affluence. For example, most costly measures to reduce human suffering
become affordable, such as high-tech medicine. Certainly, most individuals in
such societies can afford the modest costs of measures to reduce infant and
maternal mortality. Another benefit of affluence is an almost guaranteed
reduction in birth rates.
a.“Affluence is the best contraceptive.” Moderately developed countries
typically have lower fertility rates than LDCs (Table 8-3). Appreciable
population growth may still occur during this stage, especially as a result
of population growth momentum (see below) remaining from
transitional times.
b. Once a society reaches the industrial stage, restricting family size leads
to an increase in standard of living and ability to educate the next
generation. This situation is a reverse of the case in preindustrial
societies where offspring go to work at an early age to contribute to the
support of their families.
c. Points 3a and 3b above form a kind of positive feedback loop that virtually
ensures that industrialization leads to an eventual decrease in total
fertility rate (number of offspring per woman in her lifetime).
4. Postindustrial societies have either equilibrated at their maximum population
density or have entered a period of population decline following a peak at the
end of the industrial period. Even in postindustrial societies, the inverse
relationship between wealth and fertility can result in changes in the relative
population sizes of different groups within a society if discrimination, recent
immigration, or other factor produces a less wealthy subpopulation.
5. Most future growth of the world’s population is predicted to occur in countries that
are in the earliest portions of the transition stage, i.e., in less-developed
countries. (Fig. 8-16)
6. In modern times, the contraceptive effect of affluence is, of course, actually
produced through the use of contraceptive technologies (Table 8-3 and Fig. 99)
D. The age structure of a population greatly influences population dynamics. Age structure
diagrams illustrate the distribution of a population into different age and gender classes
(Fig. 8-14), using a pyramid-like double histogram with number of males per age class
on the left and females on the right.
1. It is possible for a country to have replacement-level fertility and still experience
population growth if the largest percentage of the population is in the
pre-reproductive years.
a. Replacement-level fertility is the number of children a couple must have to
contribute an average of two reproductive-age adults to the next
generation.
b. Replacement-level fertility is not a built-in property of the human species but,
instead, varies markedly as a function of the exact shape of the
survivorship curve applicable to a particular homogenous country or
subpopulation in a heterogeneous country.
c. Replacement-level fertility in highly equitable, postindustrial countries is about
2.1 children per couple, and in developing countries it is about 2.7
children. The last figure your instructor saw for the U.S. was 2.3
children per couple.
2. Such an age structure causes a positive population growth momentum. If you
ignore the male side of a country’s age-structure diagram and reverse the Xand Y-axes, the resulting histogram should have exactly the same shape as the
survivorship curve (on arithmetic axes!) for that country, IF the population is to
have no population growth momentum. If the age-structure is too “rich” at the
young end of the histogram (e.g., Fig. 8-13, left side and Fig 8-14a, Nigeria),
then built in population growth is assured when the children of the present reach
their reproductive ages, even if they all reproduce at exactly replacement levels.
If the age structure is too “lean” at the young end (e.g., Fig. 8-13 right third,
and Fig. 8-14c, Germany), then the population will shrink even if all the new
couples reproduce at replacement levels. The percentage of a country’s
population below reproductive age gives a good indicator of how much built in
momentum its age structure is likely to have (cf. Fig. 8-15).
E. The United States has one of the highest rates of population increase (0.6% in 2000) of all
the highly developed countries.
1. The U.S. population has a positive population growth momentum because of the
Baby Boom (the large wave of births that occurred after World War II) and
immigration.
2. Compared to countries like Sweden where college professors earn the equivalent of
$1000 to $1500 more per year than garbage collectors, income and wealth in
the U.S. are distributed in a much less uniform fashion. Areas and populations
can be found within the U.S. that resemble those in the developing world, so
we should not be surprised that those areas and populations have population
growth rates that are more like those of developing countries than more
homogeneous highly developed countries.
3. The Immigration Reform and Control Act (IRCA), the basic immigration law in
effect in the United States, gives three groups of people priority when migrating
to the United States: those with family members living in the United States,
those who can fill vacant jobs, and refugees seeking asylum.
II. Many human problems, such as hunger, resource depletion, environmental problems,
underdevelopment, poverty, and urban problems, are exacerbated by the rapid increase in
population.
A. The countries with the greatest food shortages also have some of the highest total fertility
rates. Much of South and Southeast Asia (except the “Asian Tigers”, like Thailand) fall
into this category, as well as most of sub-Saharan Africa.
B. Economic development, poverty, and the inequitable distribution of resources influence the
relationship between world hunger and population growth. Hopes that rising affluence
will rapidly reduce fertility in developing countries are often frustrated by the highly
inequitable distribution of income in most of those nations. Recent calls to forgive the
debts owed by the poorest of the less-developed countries are motivated in part by the
virtual certainty that these countries will be trapped in poverty and locked into a highfertility stage of the demographic transition if the debts are not erased.
C. Underdevelopment and poverty are associated with high total fertility rates. Most
economists think that slowing population growth helps promote economic development,
and vice versa.
III. In developing countries, individual resource demands are small, but rapidly increasing populations
deplete natural resources. In highly developed countries, individual resource demands are large
and deplete natural resources.
A. Nonrenewable resources are present in a limited supply and cannot be replenished in a
reasonable period. Slowing the rate of population growth will give more time to find
substitutes for nonrenewable resources as they are depleted, and to develop
technologies for the more efficient use and reuse of these resources.
B. Renewable resources are replaced by natural processes and can be used forever,
provided they are used in a sustainable way. Overpopulation causes renewable
resources to be overexploited. When this happens, renewable resources become
nonrenewable. We have already discussed fisheries as examples of over-exploitation
resulting in the near loss of potentially renewable resources (e.g., the collapse of the
Georges Bank, Fig. 1-5)
C. There are two kinds of overpopulation: people overpopulation and consumption
overpopulation.
1. People overpopulation occurs when the environment is worsening from too many
people, even if they consume few resources per person. Developing countries
have people overpopulation.
2. Consumption overpopulation occurs when each individual consumes too large a
share of resources, thereby degrading the environment. Highly developed
countries have consumption overpopulation.
D. One model of environmental impact (I) has three factors: The number of people (P), the
affluence per person (A), which is a measure of the amount of resources used per
person, and the environmental effect of the technologies used to obtain and consume
those resources (T). The model: I = P×A×T
1. This model shows the mathematical relationship between environmental impacts and
the forces that drive them.
2. The text provides the following example to build intuition:
a. P = number of U.S. drivers
b. A = ave. number of miles driven annually by each driver
c. T = ave. g of CO2 emitted per mile driven. (Note: Your instructors’s
calculations say “to calculate T, divide 7970 by gas mileage in
miles per gallon.”)
d. I = annual CO2 produced by U.S. cars.
IV. As a nation develops economically, the proportion of the population living in cities increases. As a
nation develops economically, the percentage of all city-dwellers who are female also increases,
particularly in Africa where agriculture is mostly a female enterprise.
A. The process by which people increasingly move from rural areas to densely populated cities
is known as urbanization.
B. In developing nations, most people live in rural settings, but their rates of urbanization are
rapidly increasing. Most urban growth now occurs in developing nations (Table 9-1).
This makes it difficult to provide city dwellers with basic services such as housing,
water, sewage, and transportation systems.
C. A solution to urban growth is compact development, in which cities are designed so that
multiple-unit residential buildings are close to shopping and jobs, all of which are
connected to public transportation.
1. Portland, Oregon, is a good example of compact development in a highly
developed country. Between 1975 and 2000, Portland’s population increased
by about 50%, but its urbanized area increased by just 2%. They have strict
land use policies around Portland designed to restrict suburban sprawl and
encourage reuse of “brownfields”.
2. Curitiba (pop. 2,500,000), Brazil, is a good example of compact development in a
moderately developed country. Land use policies restricted high-density
development to corridors along major bus lines, so 75% of commuters use the
buses. Curitiba’s population has doubled since 1974, but traffic has declined
by 30%.
D. Urbanization appears to be a factor in decreasing population growth. An often-cited
explanation for this observation is that distribution of contraceptives is much easier in
urban than in rural settings.
V. The relationships between total fertility rate and cultural, social, governmental, and economic factors
are many and varied.
A. A combination of four factors is thought to be primarily responsible for high total fertility
rates:
1. High infant and child mortality rates create in the minds of many parents the need to
have many children if a few are to survive to maturity.
2. The important economic and societal roles of children in some cultures. Do the kids
work in the fields or for monetary wages, or do they cost money to put through
college? In many developing countries where pension plans are not widely
available, parents are completely reliant upon their children for support and care
in their old age.
3. The low status of women in many societies. Increasing the educational opportunities
for women in many countries has coincided with decreases in fertility rates.
Better educated women often delay childbearing until they have accumulated
some wealth from the monetary wages to which education gives them access.
The contraceptive effects of affluence then seem exert themselves.
4. A lack of health and family planning services, which are particularly difficult to
distribute to the mostly rural populations typical of countries in the early
transitional stage of the demographic transition.
B. The single most important factor contributing to high total fertility rates is the low status of
women in many societies, esp. as that status affects their educational opportunities.
VI. The governments of many developing countries are trying to limit population growth.
A. In 1979 China began a coercive, one-child family policy to reduce total fertility rate. The
program, which has been successful but unpopular, was relaxed in rural China in 1984.
Education and publicity campaigns are also used today.
B. India's government has sponsored family planning since the 1950s. In 1976 India
introduced compulsory sterilization in several states, but this coercive policy failed.
Education and publicity campaigns are the focus of its family planning efforts today.
C. Mexico’s government has sponsored family planning since 1974. Mexico's total fertility
rate continues to drop, largely in response to education, improved health care,
economic development, and publicity campaigns.
D. Nigeria put a national population policy into place in 1986 that includes education,
improved health care, and economic development. These efforts have been largely
ineffective, and Nigeria's total fertility rate remains as high as it was in the early 1980s.
VII. The 1994 U.N. International Conference on Population and Development drafted a 20-year
World Program of Action that focuses on reproductive rights, empowerment of women, and
reproductive health. The program is currently underfunded, largely because funds from the
U.S., which was to have been the single largest donor country, have been withheld by
legislators in Congress who were concerned that some U.S. taxpayer dollars would pay for
abortions in developing countries. Ironically, the U. N. Population Fund estimates that
underfunding the World Program of Action will lead to 122 to 220 million unintended
pregnancies of which 43 to 88 million will end in abortion.