Notes on Human Population — Unit 1 / Chapter 8
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Topic: Human population. Course: Kennesaw State University, SCI 1102, Unit 1 / Chapter 8, Dr. T. Eugene.
Sets the stage for population biology and its environmental implications.
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World population trends (Estimates 1800–2022) and medium projection with prediction intervals for 2022–2100.
Key milestones (approximate):
1 billion around 1804
2 billion around 1927
4 billion around 1974
6 billion around 1998
7 billion around 2010
8 billion by 2022
Projections: ~9 billion by 2037; ~10 billion by 2058
Projections include 80% and 95% prediction intervals; the graph shows a median projection and two prediction bands.
The graph emphasizes that population growth is not linear and that future growth carries uncertainty.
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CO2 concentration (ppm) over time (1750–present) with last update: June 6, 2023.
Trend: steady rise in atmospheric CO2 concentration; milestones shown at historical years (e.g., pre-industrial levels around 280 ppm, rising through the 300s, 350, approaching 400+ ppm in recent decades).
Axes indicate Years (CE) vs. CO2 Concentration (ppm).
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Our World at Eight Billion: current population > 8 billion.
Growth is concentrated in least developed nations.
China is not the only country facing population-related issues; India’s policies have been more permissive, and India is projected to become the most populous country as policies in China change or loosen.
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The human population is growing rapidly: ~88 million people added per year.
This corresponds to about 2.8 people per second.
It took until after 1800 for humanity to reach 1 billion; today, ~1 billion people are added about every 12 years.
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Exponential growth: a small percentage growth rate can yield large increases when the base population is large.
This is highlighted as a key characteristic of human population growth.
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Population growth rates vary by location.
Doubling time approximation:
D ≈ 70 / r, where r is the annual percentage growth rate (as a percent).
Global doubling time with r ≈ 1.2% is about 58 years.
China’s doubling time prior to the one-child policy: D ≈ 70 / 2.8% ≈ 25 years.
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Before the industrial revolution, high birth rates were viewed positively.
Thomas Malthus argued population would outpace food supply.
Paul and Anne Ehrlich (Stanford) are described as “neo-Malthusians,” making similar warnings.
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Is population growth a problem?
Improvements in sanitation, modern medicine, and higher agricultural output have reduced infant mortality (babies dying in infancy).
Despite these gains, population growth can still be problematic due to resource depletion, social strain, and environmental degradation.
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What changed?
Even with a quadrupling of the population, predictions of doom have not fully materialized.
Food production has intensified; greater prosperity, education, and gender equality have slowed birth rates.
However, population growth continues to exert pressure on resources, social systems, and the environment.
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Other technology examples? Do they increase or decrease environmental impact?
Consider: Oil drilling, Internet, Genetically Modified Organisms (GMOs).
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IPAT model: I = P × A × T
I = environmental impact
P = population
A = affluence (per-capita consumption)
T = technology (impact per unit of consumption)
Increased population means more individuals using space, resources, and producing waste.
Greater affluence leads to higher per-capita resource use.
Technology can either increase impact (e.g., higher exploitation) or decrease impact (e.g., efficiency gains).
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IPAT visualization (P × A × T) across 1900, 1950, and 2011; three boxes representing Population, Affluence (World GDP), and Technology (Patents).
2011 example: Population Worldwide ≈ 7 billion; World GDP ≈ $55 trillion.
Historical snapshots: 1900 ≈ 1.8 billion people; 1950 ≈ 2.5 billion people; GDP around $2–$5.3 trillion (historical constant values noted).
Patents: ~412,000 (earlier snapshot), ~141,000 (mid-century snapshot), ~1.9 million (2011).
This illustrates how population, affluence, and technology have evolved and affected global impact.
2011 marker highlights a large rise in GDP and technology (patents) concomitant with continued population growth.
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Sensitivity factor S can be added to IPAT: I = P × A × T × S
Modern-day China example: various IPAT elements show environmental impact patterns.
Arid lands in western China are more sensitive to disturbance due to slow plant growth; intensive agriculture has caused erosion (Dust Bowl-like effects).
Aquifers and rivers are heavily withdrawn; air quality in Beijing is severe (breathing in Beijing can be akin to smoking 40 cigarettes per day).
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Demography: applying population ecology principles to humans is called demography.
Even with technology to keep up with growth, population ecology and logistic growth suggest growth cannot continue indefinitely.
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Demography is the study of the human population.
Demographers study:
Size
Distribution
Age structure
Sex ratio
Rates of birth, death, emigration, and immigration
Other metrics?
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The current global population is over 8 billion across ~200 nations.
United Nations projects global population to surpass 9.7 billion by 2050.
Other demographic aspects influence environmental impact beyond mere population size.
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Global population distribution is clumped; highest densities occur in temperate, subtropical, and tropical climates.
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Age Structure Diagram (Population Pyramid): describes relative numbers of individuals in each age class.
Useful for predicting future population growth.
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Population Pyramid interpretation:
Wide base indicates a large pre-reproductive cohort and potential for rapid future growth.
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Interpreting pyramids:
Even age distribution suggests a stable population.
A larger post-reproductive share indicates a shrinking population.
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Nigeria vs Canada example: Nigeria has a large concentration of young people, predicting higher future growth; Canada’s age structure is different, implying slower growth.
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Global population aging: median age today ~28; projected median age ~35 by 2050.
Implications: aging populations place strains on social welfare programs as fewer workers are available to support more elderly.
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Sex ratio at birth naturally around 106 males per 100 females.
This skew likely reflects evolutionary mortality differences.
In China, age distributions have become more skewed due to gender preferences and past policies (one-child policy).
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Cultural preference for male children plus the one-child policy led to approximately 116 boys born per 100 girls.
Hypothesis: ultrasound gender determination followed by selective abortion of female fetuses.
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Population changes result from births and immigration (increase) and deaths and emigration (decrease).
Global infant mortality declines have contributed to population growth (less “insurance” needed via many births).
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Infant mortality in China declined from about 47 per 1000 live births in 1980 to about 16 per 1000 in 2013.
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In recent decades, global growth rates declined due to falling birth rates; immigration and emigration significantly affect national population totals.
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Migration and population change:
Migration = movement between countries.
Immigration = entering a country.
Emigration = leaving a country.
People migrate for economic opportunities, conflict, or environmental degradation.
Table 8.2 (illustrative): Rates of Immigration and Emigration by Nation shows varied net migration rates by country (examples include Spain, Canada, United States, Germany, China, Mexico, Turkey, El Salvador, Lebanon, Japan).
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Total Fertility Rate (TFR): the average number of children born per woman during her lifetime.
Replacement fertility level for humans is about
TFR_{replacement} \,=\, 2.1
Industrialization, women's rights, and health care have reduced TFR in many nations.
Nearly all European nations have TFR below replacement level.
Question: How does industrialization impact TFR? (Answer: it tends to reduce TFR over time.)
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By 2015, 84 countries have fallen below replacement fertility level.
Europe’s rate of natural increase (births minus deaths, excluding migration) was between 0.0% and 0.1% in 2015.
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The Poverty Cycle (illustrative diagram):
Marry young, have young children before economic stability
Lower literacy levels
Family in debt
Limited food
Poor nutrition, sanitation, and health care
Poor school performance
Poor mental and physical development
More vulnerable to diseases
These factors interact to trap families in poverty and hinder economic mobility.
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The Poverty Cycle (alternative layout) re-emphasizing: educated, stable conditions can break the cycle; emphasis on nutrition, sanitation, health care, and education.
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Many nations are in the demographic transition:
High-income/industrialized countries tend to have higher life expectancy; infant mortality drops, increasing life expectancy.
Developing nations undergo staged changes in economy and culture, called the demographic transition.
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Demographic Transition Graph (Growth Rate vs Time) shows four stages: Pre-industrial, Transitional, Industrial, Post-industrial.
Stages described: birth and death rates; transitions due to food production, medical care, education, and gender equity.
Visual: time on x-axis; birth rate and death rate trends on y-axis; population increase occurs during transitional/early industrial stages; stabilization or decline in post-industrial stage.
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Pre-industrial stage: death rates are high from disease, rudimentary health care, and unreliable food supplies; families have many children to offset high infant mortality; no birth control; overall population growth is stable.
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Transitional period: death rates fall due to improved food production and health care; birth rates remain high; rapid population growth.
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Industrial stage: employment opportunities for women rise; birth control becomes more available; birth rates decline; growth slows and begins to stabilize.
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Post-industrial stage: population growth stabilizes or begins to shrink; United States is in this stage, though higher birth rates can occur due to immigration.
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Is the demographic transition universal?
No. It has occurred in many developed nations (Europe, Canada, U.S., Japan, etc.).
Some developing countries with high population growth may not complete the transition (demographic fatigue).
Some Global South countries, due to high birth rates and limited access to medical technology, sanitation, and economic development, may struggle to complete the transition.
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Continued discussion: demographic transition is not universal; some nations lag due to variability in development, policy, and resources.
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Will China and India complete the demographic transition?
Both are in intermediate stages; India is likely to overtake China in population size because its population-control policies are less aggressive.
Population projections (rough): China and India trajectories from mid-20th century to 2050–2060 show divergence due to policy differences.
Graph shows China and India population trajectories over time (1950–2050–2060).
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Human Population and SDG 12: Sustainable Consumption and Production
Resource and consumption patterns relate to the UN SDGs (Sustainable Development Goals).
Link/text reference: https://sdg12hub.org/
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Population and Society: What factors affect fertility?
Key factors listed:
Access to reproductive healthcare
Acceptance of reproductive health technology
Level of women’s rights
Cultural influences
Level of affluence
Dependence on child labor or low-wage labor
Availability of governmental support for retirees
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Continued factors affecting fertility (same slide reiteration of 44): emphasis on the complexity and interplay of social, economic, and policy factors.
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Family-planning programs are working around the world.
Rapidly growing countries have implemented family-planning programs, many less intrusive than China’s one-child policy.
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Fertility decreases as people become wealthier (1 of 2):
Less developed societies tend to show higher population growth than more developed ones.
Economic factors are closely tied to population growth.
Poverty exacerbates population growth; rapid growth worsens poverty.
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Fertility decreases as people become wealthier (2 of 2):
Most of the next billion added will come from developing economies; these countries will experience continued economic strain and environmental degradation due to poverty.
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Expanding wealth can escalate a society’s environmental impacts (1 of 2):
Affluence is tied to unsustainable levels of resource consumption.
The addition of one person from a highly developed country (e.g., U.S.) has a larger impact than multiple people from less developed countries (examples given: 3.4 Chinese, 8 Indians, or 14 Afghans).
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Expanding wealth can escalate a society’s environmental impacts (2 of 2):
If humanity’s ecological footprint exceeds Earth’s biocapacity, it is an ecological deficit.
If footprint is lower, there is an ecological reserve.
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Questions? The slide prompts reflection on sustainability, technology, family planning, evolution of humans, and family structures.
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Population goals support sustainable development: Fertility factors are complex and interacting; policies must be diverse, flexible, and culturally specific.
A 1994 UN conference promoted shifting from top-down birth-control policies to bottom-up approaches addressing poverty and social needs first (no one-size-fits-all solution).
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SUSTAINABLE DEVELOPMENT GOALS (17 GOALS):
1 NO POVERTY
2 ZERO HUNGER
3 GOOD HEALTH AND WELL-BEING
4 QUALITY EDUCATION
5 EQUALITY / GENDER EQUALITY
6 CLEAN WATER AND SANITATION
7 AFFORDABLE AND CLEAN ENERGY
8 DECENT WORK AND ECONOMIC GROWTH
9 INDUSTRY, INNOVATION AND INFRASTRUCTURE
10 REDUCED INEQUALITIES
11 SUSTAINABLE CITIES AND COMMUNITIES
12 RESPONSIBLE CONSUMPTION AND PRODUCTION
13 CLIMATE ACTION
14 LIFE BELOW WATER
15 LIFE ON LAND
16 PEACE, JUSTICE AND STRONG INSTITUTIONS
17 PARTNERSHIPS FOR THE GOALS