1. Darwin Presents His Case 15.3

2. Artificial Selection Selection by humans for breeding of useful traits from the natural variations among different organisms.

3. Struggle for Existence Competition among members of a species for food, living space, and other necessities of life.

4. Fitness Ability of an organism to survive and reproduce in its environment.

5. Adaptation Inherited characteristics that increases an organism’s chance of survival.

6. Survival of the Fittest Process by which individuals that are better suited to their environment survive and reproduce most successfully.

7. Natural Selection Process by which individuals that are better suited to their environment survive and reproduce most successfully.

8. Descent with Modification Principle that each living species has descended, with changes, from other species over time.

9. Common Descent Principle that all living things were derived from common ancestors.

10. Homologous Structures Structure that have different mature forms in different organisms but develop from the same embryonic tissues.

11. Vestigial Organ Organ that serves no useful function in an organism.

12. Key Concept How is natural variation used in artificial selection? In artificial selection, nature provided the variation, and humans selected those variations that they found useful.

13. Key Concept How is natural selection related to a species’ fitness? Natural selection results in changes in the inherited characteristics of a population. These changes increase a species’ fitness in its environment.