Human Population Growth World Population

The Explosion Until the beginning of the 1800’s population increased slowly and variably 1830 population reached 1 billion 1930 population doubled to 2 billion Barely 30 years later 3 billion billion billion billion billion 7 Billion National Geographic

Population Trends Prior 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 14 th 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 Increase 1800’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 High Lack of education Limited or no access to birth control Cultural/religious reasons High infant mortality rates U.S. has highest teenage pregnancy of developed countries

Birth Rates con’t U.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 Diagrams Constructed 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 ( 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 Diagrams Make population and economic projections Enables you to see the booms or busts in the age structure of a population

Population Projections Population Momentum ◦ Countries with a pyramid-shape population profile will continue to grow for 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 Transition Phase I: high CBR offset by high CDR Phase 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 Transition