The main parts of Darwin's theory of evolution by natural selection

• The Struggle for Existence

- Every species constantly competes for resources (food, water, shelter, etc.)

• The Survival of the Fittest

- The best adapted organisms of a species survive, flourish, and reproduce more so than the less-adapted, who will eventually die off.
- Over time this natural selection changes characteristics of a certain species, making them more fit for their environment.

• The descent with modifications

-Species descend with changes of their species over time.
-All living things are related to one-another, or are of common descent.

• More offspring are produced than can survive.

• Natural variation is inherited.