Essential Knowledge 1.A.1

Natural selection is a major mechanism of evolution.

According to Darwin’s theory of natural selection, competition for limited resources results in differential survival. Individuals with more favorable phenotypes are more likely to survive and produce more offspring, thus passing traits to subsequent generations.

Evolutionary fitness is measured by reproductive success.

Genetic variation and mutation play roles in natural selection. A diverse gene pool is important for the survival of a species in a changing environment.

Environments can be more or less stable or fluctuating, and this affects evolutionary rate and direction; different genetic variations can be selected in each generation.

An adaptation is a genetic variation that is favored by selection and is manifested as a trait that provides an advantage to an organism in a particular environment.

In addition to natural selection, chance and random events can influence the evolutionary process, especially for small populations.

Conditions for a population or an allele to be in Hardy-Weinberg equilibrium are: (1) a large population size, (2) absence of migration, (3) no net mutations, (4) random mating and (5) absence of selection. These conditions are seldom met.

Mathematical approaches are used to calculate changes in allele frequency, providing evidence for the occurrence of evolution in a population. Illustrative examples include:

• Graphical analysis of allele frequencies in a population.
• Application of the Hardy-Weinberg equilibrium equation.