Summary of Darwin's Theory
1. Individuals in nature differ from one another
2. Because more organisms are produce than can survive, each species must struggle for resources
3. Each organism is unique, each has advantages and disadvantages in the struggle for existence
4. Individuals best suited for the environment survive and reproduce most successful
5. Species change over time
6. Species alive today descended with modification from species that lived in the past
7. All organisms on earth are united into a single family tree of life by common descent