Darwin Presents His Case 15.3

Artificial Selection• Selection by humans for breeding of useful

traits from the natural variations among different organisms.

Struggle for Existence • Competition among members of a species for

food, living space, and other necessities of life.

Fitness • Ability of an organism to survive and

reproduce in its environment.

Adaptation

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

Survival of the Fittest

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

Natural Selection

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

Descent with Modification • Principle that each living species has

descended, with changes, from other species over time.

Common Descent

• Principle that all living things were derived from common ancestors.

Homologous Structures • Structure that have different mature forms in

different organisms but develop from the same embryonic tissues.

Vestigial Organ

• Organ that serves no useful function in an organism.

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.

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.