CHAPTER 6

• Human population growth


  Rapid rise in the last 200 years
• From the evolution of Homo sapiens to a total population of 2 billion took 200,000 years
• It took less than 50 years to add another 2 billion
• It took 25 years to add the third 2 billion
• Nineteen years later, the earth had 7.6 billion people
• Factors impacting rapid rise of human population

  • Emergence of agriculture increased food production
  • Technologies help humans expand into almost all the planet's climates and habitats
  • Drop in death rates with improved sanitation and health care
• Sustainable human population


  The maximum number of people who could live in reasonable freedom and comfort indefinitely, without decreasing the ability of the earth to sustain future generations
• Throughout most of history, population rose slowly
• China, India, and the United States are the top three countries in terms of population
• Rate of population growth

  Has slowed since 1960 to 1.2%
• 2% of population growth added to more-developed countries, 98% added to less-developed countries

  
• People are moving from rural to urban areas
• Differing views on how long the human population can keep growing

  • We have already exceeded tipping points, or planetary boundaries
  • The main problem is the rapidly growing number of people in less-developed countries
  • The main problem is overconsumption in more-developed countries
  • Technological ingenuity will help find substitutes to resources we are depleting
• Cultural carrying capacity


  The maximum number of people who could live in reasonable freedom and comfort indefinitely, without decreasing the ability of the earth to sustain future generations
• Population size increases through

  Births and immigration
• Population size decreases through

  Deaths and emigration
• Key factor that determines population size

  Average number of children born to women in a population (total fertility rate)
• Crude birth rate


  Number of live births per 1,000 people in a population per year
• Crude death rate


  Number of deaths per 1,000 people in a population per year
• Population change


  (Births + Immigration) - (Deaths + Emigration)
• Replacement-level fertility rate


  Average number of children a couple must bear to replace themselves (approximately 2.1)
• Total fertility rate (TFR)


  Average number of children born to women of childbearing age in a population
• Between 1955 and 2018, the global TFR dropped from 5 to 2.4
• To eventually halt population growth, the global TFR must drop to the fertility replacement level of 2.1
• Human population size in 2050 is estimated to be between 7.8 billion and 10.8 billion people

  
• Factors influencing the range of population estimates include reliability of current estimates, assumptions about fertility trends, and different estimation methods used by organizations
• The U.S. population grew from 76 million in 1900 to 328 million in 2018

  
• The U.S. total fertility rate has fluctuated, from 3.7 during the baby boom to 1.8 in 2018
• 40% of total U.S. population increase in 2015 came from legal immigration, and China surpassed Mexico as largest source of new immigrants
• Factors affecting birth and fertility rates

  • Importance of children as part of the labor force (especially in less-developed countries)
  • Cost of raising and educating children
  • Availability of pension systems
  • Urbanization
  • Educational and employment opportunities for women
  • Average age at which a woman has her first child
  • Availability of reliable birth control methods
  • Religious beliefs, traditions, and cultural norms
• Life expectancy


  Indicator of overall health of people in a country
• Infant mortality rate


  Number of babies out of every 1,000 who die before their first birthday
• Factors causing high infant mortality include insufficient food, poor nutrition, and infectious disease
• Migration


  The movement of people into and out of specific geographic areas
• Reasons for migration


  • Jobs and economic improvement
  • Religious persecution or ethnic conflict
  • Political oppression or war
  • Environmental refugees
• Age structure


  Number and percentages of males and females in young, middle, and older age groups in a population
• Age structure is an important factor in determining how fast a population grows or declines
• Reasons for migration


  • Jobs and economic improvement
  • Religious persecution or ethnic conflict
  • Political oppression or war
  • Environmental refugees
• Age structure


  • Important factor in determining how fast a population grows or declines
• Age structure categories


  • Pre-reproductive (ages 0–14)
  • Reproductive (ages 15–44)
  • Post-reproductive (ages 45 and older)