A random change in allele frequencies over generations brought about by chance.

Emigration

In the 1800s, hunters killed all but twenty of a large population of northern elephant seals

When allele frequencies change due to individuals leaving a population

Founder effect and bottlenecks are two extreme cases

Blue Jays introduce new alleles to oak forests as they make hundreds of round trips carrying acorns from oak trees a mile away to new soil in their home territory for winter.

May result when heterozygotes are selected AGAINST.

Phenotypic forms at both ends of the range are favored and the intermediate forms are selected against.

Type of selection that was seen in the beak size of the ground finch during times of drought

Type of selection seen where both sickle cell anemia and malaria are prevalent