Scientists not only study the populations of animals but also look at the factors that affect human population growth as well.  Demography is the study of information about human populations.  Scientists look at the birth rate, or the number of live births per 1000 people in a year, the death rate, or the number of deaths per 1000 people in a year, and the age structure of populations to determine growth patterns.  The age structure refers to the number of people at each age level, which helps predict a population’s future growth.  When a large portion of a population is children, the population experiences rapid growth.  In contrast, the population declines when there are more adults than children.  The population is stable when the percentage of people at different age levels is equal.

Human activities have affected the biosphere, particularly through agriculture and development.  Agriculture had a tremendous effect on the growth of populations. Humans began farming, clearing land, raising animals, and growing fruits, vegetables, and grains.  Human society was transformed by the industrial revolution, which added machines and factories to civilization during the 1800s.  This had a significant impact on the environment.  Discarded wastes from factories pollute the water, air, and soil.  As cities became crowded, people moved to the suburbs, which caused stress on plant and animal habitats.

Review:

1. Define demography.
2. Explain what it means when a population is experiencing rapid growth.
3. How do our activities affect the environment?