Natural Selection - Descent with Modification

Big Idea
Darwin’s first hypothesis was that evolution explained life’s unity and diversity. In other words, evolution is decent with modification.
A more formal definition of evolution is the change in genetic makeup of a population over time.
 
Characteristics of Descent with Modification

Adaptation - a trait, structure, function, or behavior that gives the organism an evolutionary advantage.

Phenotype - the expressed or physical trait of an organism.

Genotype - the actual genetic makeup that results in an expressed phenotype.

Gene pool - the actual frequency of each type of gene in a population.

Population - the smallest unit that can evolve.

Darwin’s Second Hypothesis was that natural selection is the cause of adaptive evolution.

Adaptive Radiation - a process in which organisms diversify rapidly into a multitude of new forms. 

Modes of Natural Selection:

Directional Selection - the environment selects for one extreme

Stabilizing Selection - the environment selects for the intermediate

​
Disruptive Selection - the environment selects for both extremes

Conclusion:
Natural selection is when the environment acts on the phenotype of an organism.