1. Evidence & Processes of Evolution

2. Processes of Evolution – Summary

3. Allele Frequency
Allele Frequency – the number of alleles for a specific trait that occur in a population
Ex. The number of A’s vs a’s
Natural selection shifts the phenotypic distribution away from the phenotype that is selected against

4. Mechanisms of Evolution
Natural Selection “survival of the fittest”
Mutations create new alleles
Migration moves alleles into and out of a population
Genetic drift happens when random events change the allele frequencies of small populations
Sexual Selection (non-random mating)

5. Natural Selection

6. Species
A group of organisms that can interbreed in nature and produce fertile offspring

7. Speciation – How New Species Form
Must be isolated from other populations for a long period of time.
different selection pressures cause different traits to be selected for or against.

9. Geographic Isolation
Species are separated from each other by a physical barrier

10. Geographic Isolation
The Kaibab and Albert squirrels are separated by the Grand Canyon

11. Behavioral Isolation
Species cannot interbreed because they have different mating rituals or behavior

12. Temporal Isolation
Species mate at different times of the day or the year

13. Mass Extinctions When many species disappeared from the Earth
Provides opportunity for new species to evolve and establish themselves
Mammals might not have “taken over” if the dinosaurs hadn’t gone extinct!

14. Adaptive Radiation A single species evolves into many species
Occurs as new opportunities for survival arise

15. Convergent Evolution
Unrelated organisms begin to look like each other because of similar selection pressures
These organisms would have analogous structures

16. Convergent Evolution
Sharks (fish) and dolphins (mammals) have evolved similar adaptations because of similar selective pressures

17. Coevolution
When two species evolve together in response to changes in each other
Example: Bees and Flowers

18. Evidences of Evolution

19. Homologous Structures
Similar body structures that are adapted in different ways for different organisms
Provide evidence that related organisms descended, with modifications, from a common ancestor

20. Vestigial Structures
The structures of organisms that remain from a common ancestor, but may no longer affect its ability to survive and reproduce
Example: Appendix, Tail Bone

21. Analogous Structures
Unrelated organisms in similar environments develop similar adaptations.
Example: Flight of Insects vs. Birds vs. Bats

22. Fossil Record
The fossilized remains of organisms found in the layers of rock and soil
Shows that the diversity of organisms has changed over time

23. Embryology
Organisms with a common ancestor share similar stages of development.

24. DNA Analysis
All organisms use the same four bases for their DNA (genetic code).
The more similar two sequences of DNA are, the more recent their common ancestor, or the more closely related the organisms are.

25. DNA Analysis
Modern biologists compare DNA sequences to determine which organisms are most-closely related to each other