1. Mechanisms of Evolution, cont.
Types of Natural Selection

2. Evolution is the change in allele frequency
Occurs in one of three ways:
Gene Flow
Genetic Drift
Natural Selection

3. 3) Natural Selection ~ Most common source of evolutionary change
Decreases variation
3 types

4. 1. Directional Selection
One of the extreme phenotypes is selected against
Ex: Rainfall and Bird Beaks Gizmo

5. 2. Stabilizing Selection
BOTH of the extreme phenotypes are selected against
Ex: Baby’s birth weight, gall fly size

6. 2. Stabilizing Selection

7. 3. Disruptive Selection The middle phenotype is selected against
Ex. Large and Small Bird Beaks

8. 3. Disruptive Selection

9. Natural Selection’s effect on genetic variation
Any selection that removes a phenotype is reducing genetic variation

10. Evolution leads to new species
When the gene pool of two populations become separated, they become two separate species.
Natural selection is the key mechanism of evolution that leads to speciation