Book C

Chapter 5

Changes over time

Charles Darwin -- took a trip around the world in 1831 on

a ship called the Beagle. (see p. 140-141)

-- he observed the huge variety of plants

and animals

- today we think that there are 2,500,000

different kinds of organisms

- in 1835 he came to Galapagos Islands

Here he found that many plants and animals were exactly like those on the mainland but a few had some differences.

examples:

(see p. 142)

Iguanas on the island had big claws to grasp the slippery rocks. The ones on the mainland had smaller claws.

- he decided to call these changes adaptations

(An adaptation is a characteristic of an organism

that helps it survive and reproduce.)

-he said that gradual changes in organisms over

many years would produce organisms that were better

adapted to their environment. He called this

process evolution.

- he then needed to decide what made these changes happen.

- he noticed that many organisms overproduced

offspring. (They had so many offspring that not all could

survive.)

- the offspring would compete with each other to

survive. He called this “survival

of the fittest” or natural selection