Interactive Labs

Demographics Lab

Lessons > Population Momentum > Step 1

In this lesson, we explore population momentum (the time lag between a change in birth/death rates and the slowing of population growth). In Step 1, we explore the effect of changing the age of reproduction, using Nigeria as an example. You will consider the human and ecological impacts of unchecked population growth as well as the human cost of China’s successful attempt to curb its own growth.

Select Nigeria from the Country pull down menu, run the simulator with the default settings to 2050, and record the results in your Data Table. Predict what will happen when the average age of childbearing women is increased by 5 years (fewer teenage pregnancies) and record your prediction (rise, fall, similar). Run the simulator, increasing the childbearing age by 5 years, then 15 years, and then decreasing it by 5 years, and record your results. Use the Reset button at the bottom of the dialog to restore the original rates between each different treatment.

What if Nigeria suddenly had the same birth and death rates as the USA? In the simulator, click on the birth rates button, choose “USA” from the pull-down menu, and click “Apply.” Do the same for death rates. Then, run the simulator to year 2150 (hit the Run button three times). While doing so, watch the shape of the population pyramid (the graph by age group). Sketch the pyramid shape at the end of the 150 years.

  1. How and why does the pyramid shape change?
  2. How does an increase or decrease in the average childbearing age group change the population? Why do “first world” countries tend to have older childbearing women than “third world” countries?