1. Other Factors Can Affect Genetic Variation In A Population
Natural Selection drives the evolution (change in genetic material) of a population
Other factors can cause changes in the genetic material (gene pool) of a population
Mutation
Migration
Assortative (nonrandom) mating
Genetic Drift

2. Genetic Drift Change In Allele Frequency Caused By Random Chance
Random chance = natural disasters, disease, etc.
Has a greater affect on small populations
Often causes reduction in alleles present in the gene pool.

3. The Bottleneck Affect A direct result of genetic drift
As a result of some random event, several alleles are lost from a population.

4. 3 General Types of Natural Selection
Stabilizing Selection
Directional Selection
Disruptive Selection
Nature selects the average form of a trait (human baby size)
Nature selects one extreme form of a trait (e.g. only the very long tongue in anteaters, not the short tongue)
Nature selects both the extreme forms of a trait (e.g. very bright shell and very dull shell)

5. The 3 Types of Natural Selection
Disruptive
Selection
Stabilizing
Selection
Directional
Selection

9. Sexual Selection: A Special Type of Directional Selection
Individuals of one sex (usually males) of a species are more likely to get picked as partners by the other sex if their characteristics are bolder, brighter, louder or stronger than other members of the same sex.

10. Of Course, Being More Noticeable Does Have Its Disadvantages . . .

11. Before We Go On, An Important Question: What is a species?
Members of a species are morphologically (physically) similar, and can successfully interbreed (produce fertile offspring).

12. How Do New Species Form? Isolation Isolating Mechanisms
Prezygotic Isolation
Postzygotic Isolation

13. Geographic Isolation
Physical separation of members of a population (by formation of a canyon, mountain, river, etc.)
Leads to different adaptations on each side of barrier, and eventually new species

14. Geographic Isolation = New Species: An Example
2 Species of Squirrels Formed
When They Were Separated By
The Grand Canyon

15. Reproductive Isolation
Species isolated because they reproduce in different seasons or times of day

16. Behavioral Isolation
Species Differ In Their Mating Rituals (e.g. different bird songs, mating colors, dances, pheromones, etc.)

17. Ecological Isolation Ecological Isolation
Species inhabit the same area, but different habitats, so they don’t encounter each other

18. Mechanical Mechanical Isolation Body structure prevents mating
In layman’s terms - the parts don’t fit
Famous quote in AP Bio class at PHS
“You mean it’s like trying to park a cadillac in an outhouse?”

19. Reproductive Isolation
Some barriers to successful breeding arise after fertilization and are called postzygotic isolating mechanisms
Sterile offspring (e.g. Horse + Donkey = Mule)

20. How quickly do new species form?
2 hypotheses
Gradualism
Many transitional forms between common ancestor and modern organisms
Punctuated Equilibrium
Sudden shifts in form from an ancestor to newer organism, so not many transitional forms between common ancestor and modern organisms

21. Patterns of Evolution Convergent Evolution Divergent Evolution
Adaptive Radiation
Artificial Selection
Coevolution

22. Convergent Evolution
Organisms appear similar, but aren’t closely related
Why?
Similar environment selects for similar traits

23. Divergent Evolution
Related populations or species become less and less alike
Adaptive
Radiation

24. A Second Type Of Divergent Evolution
Artificial Selection
Humans, rather than nature, select traits

25. Coevolution
Two or more species in close association w/one another change together
Predator/Prey
Parasite/Host
Plant/Pollinator

26. Finally – THE END!