The New Childrens Encyclopedia

EVOLUTION

245

 DNA This complicated

chemical is the blueprint for

life. Slight alterations in an

organism’s DNA can result

in gene changes called

mutations that are either

helpful or unhelpful to the

survival of that species.

SCIENCE

Asian

elephant

Gomphotherium Deinotherium

Phiomia

Moeritherium

THE FOSSIL RECORD

Fossils show that life on Earth has changed

throughout its history. Each major layer

of rock contains species that are slightly

different to those below or on top of it.

Although it is not easy to find fossils that

show every change in a species, this birdlike

Archaeopteryx (right), is a clear example that

birds evolved from feathered dinosaurs.

Family trees Scientists trace

evolution by examining fossils and

seeing where they fit on the family

tree. Many elephant fossils have been

found that show how these animals

developed tusks and a long trunk,

but not all are direct ancestors of

modern elephants.

HOW LIFE BEGAN

It remains a mystery how

life began. Earth was so

hot that life began in the

oceans, perhaps around

vents in the ocean floor

(right). Simple molecules

began to copy themselves,

then formed into cells

and colonies, and finally,

complicated organisms.

EVOLUTION AND GENES

Organisms use DNA to pass on their characteristics

to the next generation. DNA is divided up

into sections called genes. Every gene is a

code for a particular characteristic, such as

hair, feathers, skin, or scales.

New species When Darwin

visited the Galápagos Islands, he

noticed that all the finches looked

like a species on the mainland but

had different beaks. He realized

that all these new species had

evolved from the same parents, but

their beaks had changed to suit the

food sources on each island.

Woodpecker finch

Medium

ground finch

Vegetarian finch Warbler finch

Cabbages These

vegetables may look

different but they are all

descended from the wild

cabbage. Cabbages,

cauliflowers, broccoli,

and Brussels sprouts

have been bred for

their leaves,

flowers, or

buds.

Red cabbage

(leaves)

Brussels sprouts

(large buds)

Green cabbage

(leaves)