Britannica Student Encyclopedia - 2010

unity, or togetherness, between African

countries. Other goals are to defend the

member countries and to encourage economic

development. The AU also works

for peace and stability, the end of hunger,

and the protection of human rights.

The leaders of the AU hope to bring all

of Africa under a single, central government

someday. The AU already has its

own parliament, or lawmaking body.

The leaders are also planning a court

system for all of Africa. In addition, they

want the countries of the AU to use a

single form of money.

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Addis Ababa • Africa

Aging

All living things, from their first

moment of existence, begin the process

of aging, or growing older. As children

move toward adulthood, they become

taller, stronger, and more independent.

At some point in adulthood, however, a

slow decline begins. The onset of aging

happens at different times for different

people. Most people start to feel some

effects of aging in their 40s or 50s.

As people age, their hair often thins and

turns gray, and their skin wrinkles. Their

muscles begin to shrink and their bones

become more fragile. They often lose

some of their height or part of their

vision or hearing. They think more

slowly, and their short-term memory

may suffer. Scientists are not exactly sure

what causes the effects of aging. The

cells of the body might have a built-in

time limit. That limit would determine

how long the cells can remain healthy

and able to create new cells.

Several factors affect how long people

live. One factor is heredity. Long lives

seem to run in families. Another factor

is lifestyle. Physically fit people who do

not smoke will probably age more slowly

and live longer than others. Poverty also

affects how long people live. People who

cannot afford to eat well and go to a

doctor when they are sick may die

before they become old.

Animals age at different rates and live

for different lengths of time. These aging

People of all ages can enjoy spending time

together.

BRITANNICA STUDENT ENCYCLOPEDIA Aging 47

 

rates depend on the type of animal. Rats

may be said to be old at about 2 years,

dogs at about 10 years, and elephants at

about 40 years. For humans, people in

their 60s and older are commonly considered

to be old.

Agriculture

Agriculture is another word for farming.

It includes both growing and harvesting

crops and raising animals, or livestock.

Agriculture provides the food and many

of the raw materials that humans need

to survive.

Raising Plants and Animals

The products of agriculture that people

eat come from both plants and animals.

Plant foods include fruits, vegetables,

and grains. Meat, dairy (milk) products,

and eggs are some of the most common

animal foods.

Plants and animals also supply such

natural materials as cotton, flax, wool,

and hides.Workers process these materials

into thread, cloth, and leather. Then

people use the materials to make such

things as clothing, draperies, shoes, furniture

coverings, and many other items.

Growing trees is another important agricultural

job. Lumber from tree farms is

used to make buildings, furniture, boats,

and many other things. Christmas trees

often come from tree farms, too.

Location andWeather

People practice agriculture on farms, on

ranches, and in orchards all over the

world. Farmers raise crops and livestock

in every climate and in all kinds of different

soil. Some regions receive a lot of

sunlight or rainfall. Others have colder

or drier weather. All places have their

own kinds of agriculture.

Plants and livestock need air, water, and

nourishment to stay alive. If a plant does

not have the kind of soil it needs, it may

die. Similarly, animals also need to have

the right climate and the right food to

survive. Farmers try to raise the kinds of

livestock and plants that will do well in

their region. If they do not have perfect

natural conditions, they try to create the

best conditions possible. For example,

many farmers in dry areas use irrigation,

or artificial watering.

History

Humans may have begun taming animals

and growing small crops as early as

10,000 years ago. However, many early

people were nomads, or wanderers who

moved from place to place. They found

their foods in the wild as they traveled.

They hunted, fished, and gathered nuts,

An ox helps a man plant rice in Vietnam. berries, and roots.

48 Agriculture BRITANNICA STUDENT ENCYCLOPEDIA

 

Eventually people learned to keep some

animals in herds. They stopped roaming

and began to settle in one place for longer

times. They built homes and started to

grow their own crops on the land around

them. The crops provided a more

dependable food supply than hunting

and gathering. Small settlements grew

into villages, towns, and cities.

About 200 years ago the Industrial

Revolution brought great changes to

agriculture. In the past people had used

hand tools and animals to help them

plant and harvest. Machines invented

during the Industrial Revolution made

that work easier. As a result, not as many

workers were needed on farms. Many

people moved away from farms to cities

in search of jobs.

Today most agriculture takes place far