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Evolution
Charles Darwin
and
Natural Selection
Charles Darwin, an
English Scientist of the
19th century, was a
naturalist aboard the
British naval ship, the
HMS Beagle.
Darwin was amazed by the
tremendous diversity of
living things, especially
on the Galapagos Islands
Since Darwin’s time,
scientists have
identified 1.7 million
species of organism
on Earth.
A species is a group of
similar organisms
that can mate with
each other and
produce fertile
offspring.
Darwin noticed on the
Galapagos Islands, that
there were some species
of animals that had
slight differences to
their mainland relatives.
For instance, iguanas on
the islands have large
claws to grip slippery
rocks whereas mainland
iguanas have smaller
claws.
Darwin inferred that once
the species came to the
island, they reproduced
and eventually became
different from their
mainland relatives.
These species developed adaptations (a
trait that helps an organism reproduce).
Darwin thought the species gradually
changed over many generations and
became better adapted to the new
conditions.
Darwin’s Finches
This gradual change in a species over
time is called
EVOLUTION.
Darwin described this Theory of Evolution
in a book called
The Origin of Species.
Evolution occurs by means of Natural
Selection. Natural Selection is the
process by which individuals that are
better adapted to their environment are
more likely to survive and reproduce
than other members of the same species.
A number of factors affect
the process of Natural
Selection:
a) overproduction:
producing more
offspring than can
survive.
b) competition: food and
other resources are
limited, so offspring
must compete with each
other to survive.
c) variation: differences
between individuals of
the same species
(some animals are
darker in color than
others)
d) selection: after
many generations,
more members of
the species will
have the “helpful”
trait—the trait that
helps them survive
and reproduce.
(they’re selected)
Over a long period of
time, Natural
Selection can lead to
evolution. Helpful
variations gradually
accumulate in a
species while
unfavorable ones
Only traits that
disappear.
are inherited or
controlled by
genes can be acted
upon by Natural
Selection.
A new species can form when a group of
individuals remains separated from the
rest of its species long enough to evolve
different traits.
When Pangaea (the super-continent that
existed about 250 million years ago) split,
species became isolated from one another
and began to evolve independently.