UNIT 2 | HOW POPULATIONS GROW
OH, HOW WE’VE
GROWN!
METHOD
Students experience the changing pace of population growth by
creating a timeline that visually depicts the population doubling
through history and then actively simulating the earth’s population
growth over the last 500 years.
MATERIALS
Part 1:
• Roll of adding machine tape (7 meters of tape per group)
• Colored markers
• Meter sticks
Part 2:
• Chalk, yarn, or tape
• Population Circle counting cards
INTRODUCTION
At one time, before people knew how to prolong life with modern
medicine, better nutrition, and sanitation, the human population
grew very slowly. While there were many people being born, there
were also many people dying. In modern times, we have found
ways to prevent so many people from dying young, but there are
still many people being born. Because there are more births than
deaths in the world each year, the human population grows. Even
a small population growth rate can cause the population size to
double in a short time. Part 1 of this activity graphically illustrates
the points in history when the population has doubled. Part 2 has
students demonstrating exponential growth
in a physical simulation.
COUNTING
ON
PE PLE
K-5 Activities for Global Citizenship
CONCEPT
Over the past few hundred years,
human population has grown
exponentially, creating a “population
explosion.” The history of human
population growth is a fitting
real-world example of exponential
growth.
GRADE LEVEL
Upper elementary
SUBJECTS
Math, Social Studies, Science
OBJECTIVES
Students will be able to:
• Describe trends of human population
growth.
• Prepare a timeline that graphically
portrays population doubling through
history.
• Explain the basic attributes of
exponential growth (slow start, fast
finish).
SKILLS
Measuring in metric, multiplying,
doubling numbers, observing patterns,
critical thinking
Population Connection © 2014
PART 1: DOUBLING ON THE LINE
PROCEDURE
1. Divide the class into groups of three or four. Distribute a meter stick, a 7 meter piece of adding machine
tape, and markers to each group.
2. Explain to the class that you are going to provide data showing how world population has been growing
from the year 1510 to the present time, and then how our growth is projected to grow to the year 2025.
Post or project the World Population Growth Data chart (below) on the board. Challenge students to
determine how many years it took for the population to double, or to become twice its size.
3. Now post or project the World Population Doubling Time chart (below). Explain that students will be
converting the number of years it took for the population to double into a measurement that they will use
to create a timeline. Their timelines will depict the lengths of time it took for the human population to
double through history.
Note: If you want to students to do the conversions, cover up the “Length of Tape” column when you
project the chart.
4. Introduce the metric measurements of a decimeter and a meter and tell the class that they will be using
a scale to convert years into metric measurements. The scale is as follows: one meter is equal to 100
years, one decimeter is equal to 10 years, and one centimeter is equal to one year.
5. Tell the groups they are to construct a timeline on the adding machine paper that illustrates the number
of years it took each time world population has doubled. Starting with the year 1510, each group should
determine where the next doubling mark will be made on the timeline. This is calculated by converting
the number of years it took the population to double into the length in meters and decimeters (according
to the provided scale) and recording the measurements on the timeline.
6. Before starting the timeline, have the groups compare answers. Then, have the groups create timelines
using a different color marker to represent each doubling of the population.
7. When they’re finished, ask students what they observe about their timeline.
World Population Growth Data
Year
World Population
1510
500 million or 1/2 billion
1810
1,000 million or 1 billion
1927
2,000 million or 2 billion
1974
4,000 million or 4 billion
2025
8,000 million or 8 billion*
*projected
Unit 2 | How Populations Grow
Activity: Oh, How We’ve Grown!, Page 2
Population Connection © 2014
World Population Doubling Time
Doubling Time
Length of Tape
#1 (1510 – 1810) 300 years
3 meters
#2 (1810 – 1927) 117 years
1.17 m (1 meter + 1 decimeter + 7 centimeters)
#3 (1927 – 1974) 47 years
0.47 m (4 decimeters + 7 centimeters)
#4 (1974 – 2025) 51 years*
0.51 m (5 decimeters + 1 centimeter)
*projected
PART 2: POPULATION CIRCLE
PROCEDURE
1. Cut out the Population Circle counting cards.
2. Using chalk, tape, or yarn, create a circle on the floor about 10 feet in diameter. (If using yarn, measure
30 feet of yarn and tie the ends together.) Ask the class to form a circle around the outside of the yarn
and explain that the circle represents the earth. You will be looking at how the population of the earth
has changed over the last 500 years by simulating world population growth from 1510 to 2010. Ask
students to think about the information on the timelines they created while participating in the
simulation.
3. Distribute the 28 counting cards (if you have fewer than 28 students, you may use chairs or some other
item to represent additional people). Each card represents 250 million people. Explain to the class that
“We will be counting out loud from 1 to 100 to see how our population has grown. As we count, each
time we say a number, we are going to jump ahead five years into the future, starting at year 1510 (with
“0”) and ending at year 2010 (with “100”). When we reach 100, all 500 years will have passed. Listen for
the large number on your card and when it’s called, step into the circle. Each time someone steps into
the circle, it represents 250 million people being added to the world’s population.”
4. Ask the two students holding cards with the number “0” on them to stand in the circle to represent the
world’s population in the year 1510. Explain that the two students represent everyone who lived on
earth in 1510, about 500 million people. Today, over seven billion people live on earth.
5. Ask students to predict the number when they think the third person will enter the circle. Encourage
them to keep in mind the timeline they just made as a hint.
6. Together as a group, start counting at a comfortable pace with students entering the circle when their
numbers are called. Stop when you reach 100.
Unit 2 | How Populations Grow
Activity: Oh, How We’ve Grown!, Page 3
Population Connection © 2014
DISCUSSION QUESTIONS
1. What did you observe about how our population has changed over time, in both parts of this activity?
In Doubling on the Line, the timeline shows that in our early history, it took a very long time for the population
to double. Towards the end of the timeline, more recently, the population doubles in a fraction of the time it
took during the first 260 years. This tells us that the population is now growing very quickly.
In Population Circle, it took a long time to add anyone to the circle (not until number 51!), but towards the
end, at least one person per number was entering the circle, meaning that the population was growing very
fast.
2. Based on what you saw happening to the population, could you describe human population growth as
exponential growth?
Yes, the slow start followed by a fast and sudden increase indicates that the population is increasing in size
exponentially. Looking at the machine tape in Part 1, Doubling on the Line, the doubling time is very long in
the early years and the shorter lengths, indicating much faster population growth, occur closer to present
time. In Part 2, Population Circle, very few people joined the circle at the beginning of the counting; most
people stepped into the circle after we got to numbers in the 80s (meaning 400 of the 500 years had
passed). Growth started out very slowly but finished quickly, a sign of exponential growth.
3. What are some reasons that you can think of that have enabled people to live longer lives, and as a result,
enabled our population to increase?
Answers will vary but may include: advances in food production have led to healthier nutrition; better
sanitation has led to less disease and safer ways to dispose of human waste and garbage; medical
advancements and disease control have meant that people are living longer, healthier lives – we are now
able to cure diseases that used to be deadly; new forms of transportation have been able to move these new
technologies and new ideas at a faster pace.
4. At our current rate of growth, human population will double in about 60 years. How much further would we
have to count in Population Circle before we doubled again? How would it feel to have that many more
people in our circle?
We would need to count 12 more numbers (60/5 = 12) and add an additional 28 students (twice as many as
we started with). At the end, the circle would be holding 56 students. It would be much more crowded and it’s
likely that not everyone would fit.
5. What would happen if we continued to grow at the current rate? Can you think of any problems that would be
caused by a larger population?
The earth would become more crowded. Encourage students to think of any social issues that might occur
with a higher population and the resulting increase in resource use.
Unit 2 | How Populations Grow
Activity: Oh, How We’ve Grown!, Page 4
Population Connection © 2014
MEASURING LEARNING
Review students’ timelines and observe participation in the simulation. Monitor responses to Discussion
Questions to gauge understanding of population growth trends and exponential growth.
FOLLOW-UP ACTIVITIES
1. Put the following question on the chalkboard: “Can the earth’s population go on doubling forever?” List the
students’ answers, along with their reasoning, on the board. You may want to prompt them by asking them to
think about food supply, clean water, homes, forests, other plants and animals, and competition for
resources.
2. Now that students have completed the simulation on world population growth, follow up with the activity, The
Stork and the Grim Reaper, a visual demonstration using water and measuring cups to demonstrate how
birth and death rates determine population growth.
Unit 2 | How Populations Grow
Activity: Oh, How We’ve Grown!, Page 5
Population Connection © 2014
POPULATION CIRCLE COUNTING CARDS
POPULATION
CIRCLE
POPULATION
CIRCLE
POPULATION
CIRCLE
POPULATION
CIRCLE
POPULATION
CIRCLE
0
(1510)
0
(1510)
51
(1765)
60
(1810)
70
(1860)
POPULATION
CIRCLE
POPULATION
CIRCLE
POPULATION
CIRCLE
POPULATION
CIRCLE
POPULATION
CIRCLE
75
80
84
85
88
(1885)
(1910)
(1930)
(1935)
(1950)
POPULATION
CIRCLE
POPULATION
CIRCLE
POPULATION
CIRCLE
POPULATION
CIRCLE
POPULATION
CIRCLE
89
90
91
91
92
(1955)
(1960)
(1965)
(1965)
(1970)
POPULATION
CIRCLE
POPULATION
CIRCLE
POPULATION
CIRCLE
POPULATION
CIRCLE
POPULATION
CIRCLE
93
93
94
95
95
(1975)
(1975)
(1980)
(1985)
(1985)
POPULATION
CIRCLE
POPULATION
CIRCLE
POPULATION
CIRCLE
POPULATION
CIRCLE
POPULATION
CIRCLE
96
97
97
(1990)
(1995)
(1995)
POPULATION
CIRCLE
POPULATION
CIRCLE
POPULATION
CIRCLE
99
100
(2010)
100
(2010)
(2005)
Unit 2 | How Populations Grow
Activity: Oh, How We’ve Grown!, Page 6
98
(2000)
98
(2000)
Population Connection © 2014