Mechanisms of Evolution, cont. Types of Natural Selection

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

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

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

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

2. Stabilizing Selection

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

3. Disruptive Selection

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

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