Human Population GrowthHuman Population Growth

World Population

The ExplosionThe ExplosionUntil the beginning of the 1800’s

population increased slowly and variably

1830 population reached 1 billion1930 population doubled to 2 billionBarely 30 years later 3 billion1987 5 billion1999 6 billion2009 6.8 billion2011 7 billion7 Billion National Geographic

Population TrendsPopulation TrendsPrior to early 1800’s, the prevalence of

diseases that were often fatal caused slow growth (smallpox, diphtheria, measles, and scarlet fever) 

Epidemics such as the black plague of the 14th century, typhus, and cholera eliminated large numbers of adults

Famines Prior to 1800’s high reproductive rates

largely balanced by high mortality (especially among infants and children)

 

Reasons for IncreaseReasons for Increase1800’s Louis Pasteur and others

discovered diseases caused by infectious agents (bacteria, viruses, & parasites)

Improvement in sanitation, personal hygiene, and techniques for vaccination

1930’s the discovery of penicillin (the first in a long line of antibiotics) 

Better sanitation, medicine, and nutrition brought reductions in mortality

Exponential growth (death rates declined and birthrates remained high 

Birth Rates Remain HighBirth Rates Remain HighLack of educationLimited or no access to birth

controlCultural/religious reasonsHigh infant mortality ratesU.S. has highest teenage

pregnancy of developed countries

Birth Rates con’tBirth Rates con’tU.S. has highest rate of infant

mortality of developed countries◦inadequate health care (for poor

women during pregnancy and for their babies after birth) 

◦ drug addiction among pregnant women

◦ high birth rate among teenagers

Age Structure DiagramsAge Structure DiagramsConstructed by plotting the

percentages or numbers of males and females in the total population in each of the 3 age categories:◦prereproductive (0-14 years)◦ reproductive (15-44 years)◦postreproductive (45-85+ years)

Age structure can affect the way a population grows. ◦ The more women in the prereproductive

years and the reproductive years, the greater the increase in population growth.

Uses for Age Structure Uses for Age Structure DiagramsDiagramsMake population and economic

projections

Enables you to see the booms or busts in the age structure of a population

Population ProjectionsPopulation ProjectionsPopulation Momentum

◦Countries with a pyramid-shape population profile will continue to grow for 50-60 years, even after growth reduced to replacement level fertility

The Demographic Transition◦ the concept of a stable, non-growing

global human population based on people choosing to have smaller families

◦Epidemiologic Transition: Decline in epidemics resulted in a decline death rates 

◦Fertility Transition: Birth rates undergo a decline, takes place over decades

Phases of Demographic Phases of Demographic TransitionTransitionPhase I: high CBR offset by high CDRPhase II: declining CDR-the

epidemiologic transition, CBR remains high, phase of accelerating growth

Phase III: declining CBR resulting from a declining fertility rate, growth still significant 

Phase IV: modern stability is achieved by a continuing low CDR, but an equally low CBR

Demographic TransitionDemographic Transition