This theme comes first because the number of men and women
in the world, the distribution of populations around the globe,
and the migration patterns of people from one region to another
have always had a large effect on all other types of change.
The study of population size, density, and distribution is
called demography.
One hundred thousand years ago there may have been fewer
than a million human beings on the planet, indeed as few as
10,000. Today there are more than six billion. Compared to
other large animals, humans have multiplied at an astounding
rate in those 100 millennia. When children of today are thirty-something
in 2025, they should expect to share the earth with about
8.5 billion people. From 10,000 years ago
to 1750 CE, population world-wide increased on average by
about 67,000 people a year. By the 1990s, that many new babies
were crowding onto the planet every seven hours1.
Other large animals don't multiply in quite this way. When
a new species evolves, it multiplies to fill the new niche
for which it has evolved. For example, a bird species with
a beak specialized for breaking a particular type of nut will
multiply as long as it has enough trees to support its growing
numbers. Once it has reached that limit, its numbers will
be checked and from then on will only fluctuate modestly up
or down. It is as if the bird population was limited to the
number of individuals that the species' one new technology
(its nut-cracking beak) could support.
Things are different with humans. Because of collective
learning, they, unlike animals, have the ability
to innovate over and over again. When the population seems
to reach a limit, humans have often devised a new technology
that has allowed them to settle a new region or find new ways
to extract energy and resources from their surroundings. This
in turn has allowed the population to grow once more. In short,
human population growth has consisted of a series of leaps
forward. New skills and technologies have made these leaps
possible.
Let's divide world population growth into four major periods.
During the early paleolithic
era, from about 1.5 million years ago (when the biological
ancestors of humans first started making tools) to about
250,000 years ago, our hominid predecessors developed a
few new technologies that allowed them to spread out of
Africa and into the southern parts of Eurasia. Presumably,
their numbers rose. These changes were not very striking,
however, because other mammals, such as the ancestors of
the orangutan, had made similar migrations earlier.
During the later paleolithic era, from about 250,000 years
ago to about 10,000 years ago, things began to change. Over
this period we see more and more new technologies appearing.
These allowed early humans to explore more and more environments,
first within Africa and then elsewhere. By modern standards,
the pace of population growth was extremely slow. It was
only rapid in comparison with the pace of change of other
animals. In this era, growth was mainly the result of humans
(or their ancestors) migrating into and occupying new regions
of the world, not the consequence of increases in population
density in particular places. That is, growth was extensive,
rather than intensive. Numbers grew as humans settled more and more of the
earth, but the size and nature of each community probably
remained much the same.
The third period of growth was the agrarian age, when
people first started farming. It lasted from about 10,000
years ago to about 1700 CE, when humans began to industrialize
on a large scale. During this period, the population growth
rate world-wide was significantly greater than in paleolithic
times. Agriculture allowed humans to settle more densely,
so growth now became intensive as well as extensive. Slowly,
the very nature of human settlements began to change. As
farming technologies improved, it became possible to support
more and more people on a given area of land. Humans began
to settle in villages and small towns. And then, about half
way through this period, humans began to build cities.
About 300 years ago, global population began shooting
up fast, and the rate has continued to accelerate ever since.
Since 1700 CE, numbers have grown from about 610 million
to nearly ten times that many. Right now, five babies are
born in the world every second and only two people die.
That makes a net gain of three new people every second.
The number and size of cities in the world has also drastically
increased in the past three centuries. The crowding of our
planet has of course had an enormous impact on the way we
live. But why has it happened? Answers may be sought in
study of other transformations that may be related-industrialization
based on fossil fuel energy, advances in medicine and public
health, faster global transport and communication systems,
larger and more efficient networks of economic exchange.
Contrariwise, world population growth itself stimulates
even greater innovation in technology, communication, and
medicine to meet humankind's needs.
Human Population Growth 10,000 Years Ago to
Now
Human Population Growth
1000 CE to Now
Population charts from David Christian, Maps of Time:
An Introduction to Big History
(University of California Press, 2003), 209, 343
Population growth has by no means always been
smooth. Over the long term, demographic dips have occurred,
some of them severe. Recent genetic research in human DNA
has shown that about 100,000 years ago the existing Homo sapiens
population took a headlong dive. We can only hypothesize about
the reasons for this decline, but it may have left as few
as 10,000 adult men and women in the world. Numbers recovered, but
it took thousands of years.
In the sixteenth century CE, to cite another example, the
Indian population of the Americas may have dropped as much
as 95 percent. The principal cause was contact with people
from Eurasia and Africa, who carried a variety of infectious
diseases previously unknown in the Western Hemisphere. In
the twentieth century, wars, revolutions, genocides, epidemics,
and famines have carried off tens of millions of people within
periods of as little as a single year. None of these disasters,
however, offset the accelerating population growth of recent
times, even for a short time.
Also, changes in global population are not only a matter
of raw numbers. How many people inhabit a country, how closely
packed together they live, and how much moving and traveling
they do are all factors that affect standard of living, changes
in the natural environment, levels of crime, and many other
aspects of daily life. The steady growth of cities in the
world as a whole is one of the most important aspects of demographic
change.
Seven thousand years ago the world had no cities. The earliest
large centers arose in the Tigris-Euphrates, Nile, and Indus
River valleys between 6,000 and 4,000 years ago, though only
a tiny percentage of the world's total population lived in
them. As recently as 1800 CE, only about 3 percent of the
global population inhabited towns of 5,000 or more people.
Today, nearly half the people on the planet live in cities.
Tokyo, the world's biggest city at present, has more than
26 million inhabitants, a number about equal to the population
of the entire planet just 4,000 years ago. Of the twenty-five
biggest cities in the world today, only two are in the United
States. Some cities have become big so recently that many
Americans might have trouble locating them. Among the top
twenty-five are Tianjin, Osaka, Karachi, and Lagos. Can students
find them on a map?
A Crowded Metro Train
in Moscow R. Dunn
The 50 percent or so of the world's population that does
not inhabit cities lives in rural areas, that is, in villages
or in homesteads scattered in the countryside. About 25 percent
of the population of the United States is rural; in Britain
it is less than 10 percent. By contrast, the population of
the African continent is about two-thirds rural. Country living
does not mean, however, that people necessarily have plenty
of room for themselves and their farms. Rural population density
can be very high. On the island of Java in Indonesia, for
example, there are about 2,000 people per square mile, but
most of them are farmers, not city folk.
Travel and migration have been important to the story of
population growth in the past 100,000 years. By about 12,000
years ago, humans inhabited all the major land areas of the
world except Antarctica. All of them made their living by
hunting, gathering, or fishing, Since then, people have continued
to move and migrate, sometimes short distances, sometimes
very long ones. The placement, or distribution of people in
the world has been constantly changing.
Cities have always attracted newcomers from the countryside
because cities have been centers of trade, manufacturing,
religious worship, government, social support, and cultural
variety. In ancient and medieval times men and women flocked
to bustling cities like Babylon, Rome, Cairo, Hangzhou, and
Teotihuacan. Today, people are migrating in huge numbers from
countryside to city and from country to country. Most of them
are looking for jobs and better standards of living, though
they don't necessarily find those things when they reach their
destination. About three-quarters of American children live
in cities. What does city-dwelling offer that living in a
small town or on a farm does not? What are the disadvantages
of urban living today?
Finally, we should remember that the presence of such colossal
numbers of human beings on the face of the planet affects
the entire biosphere. Some animals, such as sheep, cows, rats,
and pigeons, have flourished in association with human communities.
Far more species, however, have been driven to extinction, or
to the brink of it, as humans have taken up more and more
of the space and resources that other species need to survive.
So, as you consider other Key Themes, remember that in world
history-whether 100,000 years ago, two centuries ago, or today-growth,
decline, and movement in human population is often a causative
factor in explaining changes in other aspects of life.
Conditions of population growth and density have a huge
impact on how people live, work, and get along together.
In the long run of human history, the presence today of
more than six billion people on the planet represents a
recent and drastic change. This fact, together with the
constant flux in worldwide population movement and distribution,
affects our daily lives in countless ways.
In today's schoolroom, students are more likely than
ever to have been born in some other country or to be the
child of recent immigrants. About 25 percent of the population
living in the U.S. today was born outside its borders. This
reality suggests the value of understanding not only differences
in cultural beliefs and practices among America's population
but also the patterns of global migration and urbanization
that have become so complex in our own world.
Questions for Classrooms
Landscape Teaching Units that Emphasize
Key Theme 1:
[In Development]
Footnotes:
1
John R. Weeks, Population: An Introduction to Concepts
and Issues, 6th ed. (Belmont, CA: Wadsworth, 1996), 34.
