Biology 12

Chapter 15 Human Ecology • MHR 511

Republic of Congo’s actually have fertility rates that
are declining to near replacement level. However,
these populations will continue to grow rapidly for
a period because so many females are in or nearing
their reproductive years. Populations like this, with
a large proportion of young individuals, are often
said to have a momentum for growth.
As you have seen, age pyramids are one tool
demographers use to help them examine a
population’s potential for growth and determine
its stage of demographic transition. The next
Thinking Lab will help test your understanding of
how age pyramids are created and how they can
be used.

Urbanization

From artifacts, historical records, and observation
of similar human groups existing today, we know
that hunter-gatherer societies typically exploited
(or exploit, in the case of the few remaining modern
societies) many different resources lightly, rather
than relying heavily on only a few. They often moved
seasonally, using different food sources as they
became available. Their need for mobility and their
typically subsistence-level lifestyle provided no
incentive for large families and their birth rate was
therefore generally low. Because their populations
were small and nomadic, their accumulation of
waste (material and human) was minimal and easily
handled by Earth’s natural processes. Therefore,

for many reasons, hunter-gatherer societies had

relatively little impact on the environment.

Around 10 000 years ago a new lifestyle emerged.

It may have been spurred by the retreat of the last

ice age, which left behind a warmer climate and

fertile soils. Agriculture, the sowing and harvesting

of crops, and the domestication of animals paved

the way for a more sedentary lifestyle. It also set

the stage for the development of what is referred

to as civilization — the appearance of a highly

organized society, characterized by the use of

written language and advances in government,

the arts, and the sciences.

The earliest agricultural sites in the world have

been found in the Near East (in what is now

Turkey), the Nile Valley, and Mesopotamia (the

region east of the Mediterranean Sea between the

Tigris and Euphrates rivers). The fertile soil and

hot climate in these areas made it possible to

harvest several times each year. Farmers planted

fields of wheat and barley, which grew naturally

on forested hills above the plain. Because these

cereals did not provide all the proteins needed by

humans, it was also necessary to eat meat — a

commodity supplied by domesticated animals.

Farming provided a relatively predictable and

abundant food supply, but it was also labour

intensive, requiring many hands to bring in a crop.

These factors favoured large families, and the

human population began its inexorable increase.

810 0246 2 46810 024 42 024 42

Age

80 +

75 – 79

70 – 74

65 – 69

60 – 64

55 – 59

50 – 54

45 – 49

40 – 44

35 – 39

30 – 34

25 – 29

20 – 24

15 – 19

10 – 14

5 – 9

0 – 4

Year of birth

before 1920

1920 – 24

1925 – 29

1930 – 34

1935 – 39

1940 – 44

1945 – 49

1950 – 54

1955 – 59

1960 – 64

1965 – 69

1970 – 74

1975 – 79

1980 – 84

1985 – 89

1990 – 94

1995 – 99

male

Percent Percent Percent

female male female male female

Rapid growth

Democratic Republic of Congo

Slow growth

United States

Negative growth

Germany

Three patterns of population change, 2000

Figure 15.6Age pyramids for three countries with different
age structures. What is the ratio of post-reproductive
individuals (those past their reproductive years) to

pre-reproductive and currently reproducing individuals

in each country? How will this affect the future growth

of the population?