1. Natural selection is not the only mechanism through which populations evolve.

2. Gene flow is the movement of alleles between populations.
occurs when individuals join new populations and reproduce.
keeps neighboring populations similar.
Low gene flow increases the chance that two populations will evolve into different species.
bald eagle migration

3. Genetic drift- a change in allele frequencies due to chance.
causes a loss of genetic diversity.
most common in small populations.

4. The Bottleneck Effect- genetic drift that occurs after an event greatly reduces the size of population.
* Alleles can be lost
Examples
Over Hunting
Natural Disasters

5. The founder effect- genetic drift that occurs after a small number of individuals colonize a new area.

6. Sexual selection- occurs when certain traits increase mating success.