Darwin's Theory

• A species is a population of organisms that interbreeds and has fertile offspring.


• Living organisms have descended with modifications from species that lived before them.

Natural selection explains how this evolution has happened:

1. More organisms are produced than can survive because of limited resources.
   


2. Organisms struggle for the necessities of life; there is competition for resources.
   


3. Individuals within a population vary in their traits; some of these traits are heritable -- passed on to offspring.
   


4. Some variants are better adapted to survive and reproduce under local conditions than others.
   


5. Better-adapted individuals (the "fit enough") are more likely to survive and reproduce, thereby passing on copies of their genes to the next generation.

6. Species whose individuals are best adapted survive; others become extinct.