the century. The total added will be about 2.5 billion people, which is more than were even
in existence as recently as 1950.
With so many more people on the planet than ever before, we must ask whether humans
now are exceeding Earth’s carrying capacity for our species. Many anthropologists say that
the carrying capacity of humans on the planet without agriculture is about 10 million. This
population was reached about 10,000 years ago. At the time, people lived together in small
bands of hunters and gatherers. Commonly women gathered nuts and vegetables and men
hunted animals and fished. People within a band shared their resources. Although they
had trading networks with outside groups, trading was limited by what could reasonably be
carried. For the most part, people relied on the resources that they could find where they
lived.
As you can see, human populations have blown past this hypothetical carrying capacity.
By using our brains, our erect posture, and our hands, we have been able to do things
that no other species has ever done. About 10,000 years ago, we developed the ability
to grow our own food. Farming allowed us to grow the plants we wanted to eat and to
have food available year-round. We domesticated animals to have meat when we wanted.
With agriculture, people could settle down, so that they no longer needed to carry all their
possessions. They could develop better farming practices and store food for when it was
difficult to grow. Agriculture allowed people to settle in towns and cities. Early farmers
could grow only enough food for their families, with perhaps a bit extra to sell, barter, or
trade. More advanced farming practices allowed a single farmer to grow food for many more
people. Being freed from having to gather or grow food allowed people to do other types of
work.
The next major stage in the growth of the human population was the Industrial Revolution,
which started in the late 1700’s. Increased efficiency in farming freed up large numbers of
people available to work in factories. This major historical event marks when products were
first mass produced and when fossil fuels were first widely used for power.
Every major advance in agriculture allowed global population to increase. Irrigation, the
ability to clear large swaths of land for farming efficiently, and the development of farm
machines powered by fossil fuels allowed people to grow more food and transport it to where
it was needed. Currently about 70% of the world’s fresh water is used for agriculture.
The biggest advance in agriculture in recent decades is called theGreen Revolution. It
is this advance that has allowed the population to grow so rapidly. The first focus of the
Green Revolution was to improve crops. A tremendous increase in the use of artificial
fertilizers, nutrients that help plants to grow and chemical pesticides, chemicals that kill
pests followed. About 23 times more fertilizer and 50 times more pesticides are used around
the world than just 50 years ago. Most agricultural work is now done by machines: plowing,
tilling, fertilizing, picking, and transporting (Figure18.23). About 17% of the energy used
each year in the US is for agriculture.
The Green Revolution has increased the productivity of farms immensely. A century ago,