Darwin published his theory of evolution with compelling evidence in his 1859 book On the Origin of Species.

Read the text about Darwin's theory of evolution.

The Theory of Evolution

Charles Darwin based his theory of evolution on his observations as a naturalist. He noticed that animals produce more young than they need to replace themselves. He also noticed that animals of the same species can be different, and that the young inherit these differences from their parents. Imagine a bird species. One day a bird is born with a beak that is longer than the beak of other birds in the species. Perhaps this longer beak helps the bird to catch more food. Because the bird can catch more food, it is healthier than the other birds. 1) It will possibly live longer as a result.

The chicks inherit the gene for the longer beak. They also live longer and therefore have more chicks. The gene continues from generation to generation. 2) Eventually, it is possible that all the birds in the species will have the longer beak. 3) We are certain that this process takes thousands of years. The better adapted animals are more successful.  4) When a species cannot evolve fast enough, it is possible for it to die out. 5) Perhaps this explains the disappearance of the dinosaurs. Darwin's Theory of Evolution is based on what we can see now. 6) It is not possible for us to be sure that it is correct. That is why it is a theory and not a law.

Rewrite the sentences in bold using the words given.

Example: Perhaps this longer beak helps the bird to catch more food.

(might) This longer beak might help the bird to catch more food.

1) (may) It   longer as a result.

2) (could) Eventually, all the birds in the species    the longer beak.

3) (must) This process   thousands of years.

4) (can) When a species cannot evolve fast enough, it   as a result.

5) (might) This   the disappearance of the dinosaurs.

6) (can't) We   that it's correct.