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

EVOLUTION.

This gradual change in a species over time is called

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 disappear.

Only traits that 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.