1. Bell-Ringer: 2/10-PHONES AWAY
Clear your tables for quiz!

2. 2/14-phones away! Have your stamp sheet and crossword puzzles out!
Stamp #14-Crossword puzzle
Evolution quiz on Friday!

3. 2/14-phones away!
Evolution Enrichment Test on Friday

4. Types of Selection

5. Types of Selection
Selective Pressure:  Environmental factors which may reduce reproductive success in a population
Examples of selective pressure: Competition, predation, climate, food, disease

6. Why do Robins (bird) lay only 3-4 eggs?
Explanation: Larger clutches may result in malnourished chicks while smaller clutches may result in no viable offspring
This is an example of stabilizing selection where the average is favored

7. Original Population

8. Stabilizing Selection
Definition: Natural selection favors the average for population selected. Decreases genetic diversity
When the extremes of the trait aren’t as well suited
Examples
bird clutch size
Human birth weight
Human height

9. Examples of stabilizing selection

10. Examples of stabilizing selection

12. Why do Giraffe have long necks?
Explanation: the giraffe need long necks to eat the leaves on the tree
This is an example of directional selection: Where one extreme trait is favored

13. Directional Selection
Definition: Natural selection favors one extreme of the population for that trait
Examples:
Neck of Giraffe
Antibiotic resistance of bacteria
Moth color (melanin)
Camouflage/Mimicry

14. Examples of Directional Selection

15. Example of Directional Selection

16. Directional Selection: Mimicry (mimic environment)

17. Why are there still two different fur colors of rocket mouse?
Explanation: There are still two different types of ground in the area, sandy and dark lava
This is an example of Disruptive selection where both “extremes” are favored

19. Disruptive Selection
Definition: Natural selection favors both extremes selected
Causes species to diverge
Occurs when two different types of resources in one area
Results in specialization for each branched group
May lead to formation of new species
Examples:
Darwin’s Finches (different beak sizes)
Rock Pocket Mouse fur color
(Black or white)
Short vs. Long beak humming birds

20. Examples of Disruptive Selection

21. Examples of Disruptive Selection

24. Main Types of Selective Pressures
Stabilizing Selection
Natural selection favors the average for population selected
Directional Selection
Natural selection favors one extreme of the population for that trait
often happens when environment changes in a consistent way- e.g.climate gets colder.
Disruptive Selection
Natural selection favors both extremes selected
Causes species to diverge