Human population
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8. Human Population. Age structure: Age pyramids. Canada (a) shows a balanced age structure, while Madagascar’s population growth (b) is 9 times faster. Age structure: “Graying populations”. China’s aging population will mean fewer working-age citizens to finance social services for retirees.

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Human Population

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Human Population

Age structure: Age pyramids

Canada (a) shows a balanced age structure, while Madagascar’s population growth (b) is 9 times faster.

Age structure: “Graying populations”

China’s aging population will mean fewer working-age citizens to finance social services for retirees.

Age structure: “Baby booms”

The United States’ “baby boom” is evident in age bracket 40–50. U.S. age structure will change as baby boomers grow older.

Sex ratios

  • A population’s sex ratio can affect its growth rate.

  • The naturally occurring sex ratio in humans is 105 to 106 males for every 100 females.

  • This may be an evolutionary adaptation as males are slightly more prone to death at any given age.

  • The ratio of men to women is therefore approximately equal at reproductive age.

Factors affecting population growth rates

Population growth depends on rates of birth, death, immigration, and emigration.

(birth rate + immigration rate)

– (death rate + emigration rate)

= population growth rate

Migration can have environmental effects

Immigration and emigration play large roles today.

Refugees from the 1994 Rwandan genocide endured great hardship, and deforested large areas near refugee camps.

China’s natural rate of change has fallen

China’s rate has fallen with fertility rates. It now takes the population 4 times as long to double as it did 25 years ago.

Global growth rates have fallen

The annual growth rate of the world population has declined since the 1960s.

(But the population size is still rising!)

Fertility rates affect population growth rates

  • Total fertility rate (TFR) = average number of children born per woman during her lifetime

  • Replacement fertility = the TFR that keeps population size stable

  • For humans, replacement fertility is about 2.1.

Total fertility rates by region

African nations have the highest TFRs.

European nations have the lowest TFRs.

Natural rate of population change

  • Change due to birth and death rates alone, excluding migration.

  • It is often expressed in % per year.

Demographic transition theory

  • Demographic transition = model of economic and cultural change to explain declining death rates, declining birth rates, and rising life expectancies in Western nations as they became industrialized.

  • Proposed by Frank Notestein in the 1940s–1950s

Demographic transition: Stages

The demographic transition consists of several stages:

  • Pre-industrial stage: high death rates and high birth rates.

  • Transitional stage: death rates fall due to rising food production and better medical care. Birth rates remain high, so population surges.

Demographic transition: Stages, continued

  • Industrial stage: birth rates fall, as women are employed and as children become less economically useful in an urban setting. Population growth rate declines.

  • Post-industrial stage: birth and death rates remain low and stable. Society enjoys fruits of industrialization without threat of runaway population growth.

Demographic transition: Stages

TFR decline in Bangladesh

Bangladesh reduced TFR from 7.1 to 4.6 in 25 years, and is at 3.0 today.

Family planning, education, and outreach were responsible.

Female education and TFR

  • Female literacy and school enrollment are correlated with total fertility rate.

  • More-educated women have fewer children.

Family planning and TFR

Family planning, health care, and reproductive education can lower TFRs.

The Matlab Project provided visits from local women offering counseling, education, and free contraceptives.

Women still need more empowerment

Women are vastly under represented in positions of political power. In national legislatures, women make up at best 45% of seats, and in some countries, 0%.

Poverty is correlated with population growth

Poorer countries will experience most future population growth

98% of the next billion people born will live in developing nations.

Population and the environment

Population growth can lead to environmental degradation.

Overpopulation in Africa’s Sahel region has led to overgrazing of semi-arid lands.

Affluence and the environment

Poverty can lead to environmental degradation…


wealth and resource consumption can produce even more severe and far-reaching environmental impacts.

The ecological footprint

The cumulative amount of Earth’s surface area required to provide the raw materials a person or a population consumes, and then to dispose of or recycle the waste that is produced.

Global ecological footprint

Scientists have calculated the global ecological footprint now exceeds what the Earth can bear in the long run.

The wealth gap

  • Residents of developed nations have larger houses, more possessions, and more money than residents of developing nations.

  • The richest 20% of the world’s people consumes 86% of its resources, and has > 80 times the income of the poorest 20%.

HIV/AIDS and human population

AIDS cases are increasing rapidly worldwide.

HIV/AIDS and human population

  • Infects 1 in 5 people in southern African nations

  • Kills babies born to infected mothers

  • Has orphaned 14 million children

  • Has cut 19 years off life expectancies in parts of southern Africa

Demographic fatigue and demographic transition

  • Many governments of developing countries are experiencing “demographic fatigue,” unable to meet the social, economic, and environmental challenges imposed by rapid population growth.

    This raises the question:

  • Will today’s developing countries successfully pass through the demographic transition?


  • The human population is larger than at any time in the past.

  • 90% of children born today are likely to live in conditions far less healthy and prosperous than those in the industrialized world.

  • The rate of growth has decreased nearly everywhere, and some countries are seeing population declines.

  • Most developed nations have passed through the demographic transition and are in position to transition to ecologically sustainable economies.


  • Many developing nations are making their way through the demographic transition, and equitable treatment is vital to their success.

  • Women’s rights are expanding worldwide, which helps slow population growth.

  • Sustainability demands that we stabilize our population size before destroying the natural systems that support our economies and societies.

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