C4

Foundations of Population and Demography

• Population is defined in human biology as the total number of inhabitants occupying a specific area, such as a country or the entire world.
• This inhabitant count is continually modified by two forms of increases (births and immigrations) and two forms of losses (deaths and emigration).
• Biological limits on human population size include the food supply, the effects of various diseases, and additional environmental factors.
• Human-specific influences on population include:
  • Social customs that govern reproduction.
  • Technological developments, specifically in the fields of medicine and public health, which have served to reduce mortality and extend human life spans.

Processes of Population Change

• Populations change through three primary processes:
  • Fertility: This involves the number of children that women actually have.
  • Mortality: The study of the causes, consequences, and measurement of the processes that affect death among members of a population.
  • Migration: The movement of persons from a locality of origin to a destination place across a pre-defined political boundary.

Factors Influencing Reproduction and Fertility

• Demographers distinguish between two key reproductive concepts:
  • Fecundity: The underlying biological potential for reproduction or a woman's childbearing potential.
  • Fertility: The actual level of achieved reproduction recorded in a population.
• Several intervening factors determine the difference between biological potential and realized fertility:
  • Most women do not start reproducing immediately at the onset of puberty, and the age of puberty itself is not fixed.
  • Some women who possess the biological potential to reproduce never do so.
  • Widowhood without remarriage reduces the period of reproductive opportunity.
  • Social behavior elements act as restraints on fertility.
  • Couples often make conscious choices to restrict fertility through sexual abstinence, contraception, abortion, or sterilization.

Global Population Trends and Projections

• Between the years $2011$ and $2012$, the global population reached a milestone of $7 \text{ billion}$ humans.
• The growth from $5 \text{ billion}$ to $6 \text{ billion}$ people demonstrated an exponential increase, indicating the rapidity with which the planet is filling.
• Global human population growth is approximately $83 \text{ million}$ people annually, representing a rate of $1.1\%$ per year.
• Historical and projected population milestones include:
  • Year $1800$: $1 \text{ billion}$.
  • Year $2017$: $7.6 \text{ billion}$.
  • Mid-$2030$: Estimated $8.6 \text{ billion}$.
  • Mid-$2050$: Estimated $9.8 \text{ billion}$.
  • Year $2100$: Estimated $11.2 \text{ billion}$.
• There is a correlation between growth and living standards:
  • Nations with rapid population growth often have low standards of living.
  • Nations with low rates of population growth often have high standards of living.

Theoretical Perspectives on Population Growth

• The "Modern Rise of Population" began in the Western world during the Industrial Revolution in the late $18^{\text{th}}$ century.
• British health scientist Thomas McKeown ($1912$-$1988$) investigated this rise and challenged four existing theories.
• The McKeown Thesis maintains:
  • The surge in the Western population during the $19^{\text{th}}$ century was caused largely by a decline in mortality rather than an increase in fertility.
  • This mortality decline focused specifically on childhood mortality followed by infant mortality.
  • The primary driver for reduced mortality was rising standards of living, with the greatest emphasis placed on nutritional status.
• Controversial aspects of McKeown's work:
  • He questioned the effectiveness of public health measures such as sanitary reforms, vaccination, and quarantine.
  • He argued that curative medicine played a minimal role in the mortality decline prior to the mid-$20^{\text{th}}$ century and well into the $20^{\text{th}}$ century.

Biological Concepts: Biotic Potential and Carrying Capacity

• Biotic potential is the ability of a population of a living species to increase under ideal environmental conditions, which include a sufficient food supply, the absence of predators, and a lack of disease.
• Determining factors for biotic potential include the rate of reproduction and the size of each litter.
• Species differences in biotic potential:
  • Large mammals like humans or elephants have low potential, typically producing only one offspring per year.
  • Small organisms like insects have high potential, often producing thousands of offspring per year.
• Environmental resistance prevents most species from fulfilling their biotic potential due to factors like predators, disease, environmental changes, or lack of food.
• Human growth sustains despite low biotic potential because of mechanisms to treat disease, the ability to produce food, and a lack of natural predators.
• Carrying capacity is the maximum number of a given species that can be sustained by resources in a given environment.
• When a population nears carrying capacity, resource consumption equals resource production, leading to competition, increased mortality, and reduced reproduction, preventing the fulfillment of biotic potential.

Formal and Social Demography

• Demography is the statistical study of human populations, derived from the prefix "demo" (the people) and "-graphy" (writing, description, or measurement).
• It encompasses the size, structure, distribution, and changes in populations over time (temporal) and space (spatial) in response to birth, migration, aging, and death.
• Formal Demography: Limits its object of study to the measurement of population processes.
• Social Demography (Population Studies): Analyzes the relationships between economic, social, cultural, and biological processes that influence a population.
• Demography is usually treated as a field of sociology in educational institutions.

Methods of Demographic Data Collection

• Direct Methods:
  • Vital Statistics Registries: These track births, deaths, and legal status changes such as marriage, divorce, and migration/residence registration. These are the best methods for developed countries like the United States and much of Europe.
  • Census: A national government effort to enumerate every person in a country. Typically conducted every $10$ years, it is usually less effective for tracking immediate births and deaths than vital registries.
  • Censuses collect data on families, age, sex, marital status, education/literacy, employment, occupation, location, language, religion, and ethnicity. In countries with incomplete registries, like the People's Republic of China, censuses may gather birth and death data from the preceding $18$ months.
• Indirect Methods:
  • These are required when full data are unavailable, particularly in the developing world or in historical demography.
  • Sister Method: Survey researchers ask women how many of their sisters have died or had children and at what age to estimate population-wide rates.
  • Other methods involve asking individuals about their siblings, parents, and children.

Mathematical Indicators: Common Rates and Ratios

• Crude Birth Rate: The annual number of live births per $1,000$ people.
• General Fertility Rate: The annual number of live births per $1,000$ women of childbearing age, usually defined as age $15$ to $49$ (sometimes $15$ to $44$).
• Age-Specific Fertility Rates: The annual number of live births per $1,000$ women in specific age cohorts (e.g., $15$-$19$, $20$-$24$).
• Crude Death Rate: The annual number of deaths per $1,000$ people.
• Infant Mortality Rate: The annual number of deaths of children less than $1$ year old per $1,000$ live births.
• Expectation of Life (Life Expectancy): The number of years an individual at a given age can expect to live based on current mortality levels.
• Total Fertility Rate: The number of live births per woman completing her reproductive life, assuming childbearing at each age reflects current age-specific fertility rates.
• Replacement Level Fertility: The average number of children women must have to replace the population for the next generation. In the United States, this value is approximately $2.11$.
• Gross Reproduction Rate: The number of daughters who would be born to a woman completing her reproductive life at current age-specific fertility rates.
• Net Reproduction Ratio: The expected number of daughters per newborn prospective mother who may survive through the ages of childbearing.
• Stable Population: A population with constant crude birth and death rates over a long period, resulting in a constant percentage of people in every age class and an unchanging population pyramid structure.
• Stationary Population: A population that is both stable and unchanging in total size, where the difference between the crude birth rate and crude death rate is zero.

Questions & Discussion

• Describe the work of public health educators in promoting healthy environments, habits, and behaviors.
• What is the purpose and guiding principle of the PRECEDE-PROCEED model? Explain.