High school biology Assignments

Power of Pyramids

Background:

Many of the vast differences we see in societies across the globe can be related to the composition of their respective populations. This is true on the local, state, and national level. So when exploring variations among countries, a good place to start is with their population pyramids – graphs that display the age and sex distribution of the country’s population.

To help make population projections for different countries, demographers look at the profile of the countries’ residents. What are the ages of the people? How many are men? How many are women? Taking this information, they construct population pyramids that depict the configuration of a country’s population as impacted by 70 to 80 years of economic, political, and natural events.

For example, here is a Population Pyramid for the World for 2017.

This graph represents the entire world population, sorted by age and sex – with the youngest at the bottom and the oldest at the top and males on the left, and femailes on the right. Each age level/sex grouping is called a cohort. A cohort represents the percentage of people within that sex and age range within the population. So from this pyramid we see that 4.5% of the global population is made of of males aged 0-4. This is the largest cohort since that bar extends the furthest from the center axis.

We can use the shape of the pyramid to predict the type of population growth that is occurring. There are three groups of cohorts based on reproductive categories. The younger group, Pre-Reproductive, has cohorts between 0 and 14 years. The middle group, Reproductive, has cohorts between 15 and 44 years and the older group, Post-Reproductive, has cohorts above 45 years.

As we look at the pyramid for Ethiopia, we can see that it will be a Growing population. A significant percentage of people are in the pre-reproductive age groups. As those children age and enter their reproductive years and start having children of their own, the population will almost surely grow.

The pyramid for New Zealand shows a Stable population. The rectangular shape shows a fairly even distribution of people across each age group. Generations are replacing each other so the poupulation will not grow or shrink.

The cup shape pyramid of Japan shows a shrinking population. The largest percentage of people are in their post-reproductive years and no longer having children. As fewer and fewer people reach reproductive age, the size of the population will decrease.

Procedure:

1. Print out at least two pages of Pyramid Graph Paper (you can print out more if you would like to do all six countries).

2. Print out the Power of the Pyramids Worksheets.

3. Using the Data for the United States, calculate the percentage of the population of each sex in each age group and record your answer on the Worksheet. For example, the total population of the United States in 2017 was 326,625,791. The population of U.S. males aged 0-4 years was 10,310,369.