1. Types of Selection

2. Review What is evolution? What is natural selection?
If a population contains both white and black furred rabbits that live in a snowy area, over time what kinds of rabbits do you predict will become more common?

3. Natural Selection
Organisms most fit for their environment are most likely to reproduce
Fitness = the ability to survive in your environment
Adaptation = any trait that increases your survival chance.
Common descent = all organisms are related.

4. Natural selection can favor or not favor a trait
Types of Selection
Natural selection can favor or not favor a trait

5. Directional Selection
An extreme of a trait is favored
Example: Either extreme tallness or extreme shortness are favored

7. Stabilizing Selection
Neither extreme is favored
A middle value is favored instead
Example: A middle value for birth weight is favored in humans

9. Disruptive Selection Both extremes are favored, but the middle is not
Opposite of stabilizing

10. Example of Disruptive Selection
Beak size in birds

12. Genetic Drift
Random changes in the frequency of a trait due to small population sizes
The trait that becomes more common is not necessarily the most fit

13. Still leads to evolution
Genetic Drift
NOT SELECTIVE
Still leads to evolution

15. Founder effect
Genetic drift caused by a small group colonizing a new home
Example: Polydactyly (extra fingers or toes) is far more common in the Amish ]