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

3. Convergent Evolution
Organisms appear similar, but aren’t closely related
Why?
Similar environments select for similar traits

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

5. Adaptive Radiation
Generally means an event in which a lineage rapidly diversifies, with the newly formed lineages evolving different adaptations.

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

7. One More Example of Artificial Selection

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

9. On the Origin of Species by Means of Natural Selection (1859)
Summary of Theory of Natural Selection:
1. Overproduction of offspring
2. Struggle to survive  competition
3. Variation within population
4. Successful reproduction – “survival of the fittest” (best adapted organisms are “naturally selected”)
Overproduced variations struggle to successfully reproduce… 9

10. Fitness
The success of an individual in surviving and reproducing.

12. Natural Selection
Natural Selection acts on a POPULATION, not an INDIVIDUAL!
An individual influences this based on his / her fitness.

13. 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)

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

15. 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.

16. Sexual Selection in Peacocks

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

18. Other Factors Can Affect Genetic Variation In A Population
Other factors besides meiosis/sexual reproduction and mutations create the variation in the genetic material (gene pool) of a population on which natural selection acts
Migration
Assortative (nonrandom) mating = sexual selection
Genetic Drift

19. DNA frequency in a population changes simply by CHANCE not fitness
GENETIC DRIFT
DNA frequency in a population changes simply by CHANCE not fitness
Survivors are lucky, not more fit
Deceased are unlucky, not less fit 19

20. Genetic Drift Change In Allele Frequency Caused By Random Chance
Random chance = natural disasters, disease, hunting, etc.
Has a greater affect on small populations
Often causes reduction in alleles (not always the weakest alleles) present in the gene pool.

21. some individuals of a population colonize a new habitat
Types of Genetic Drift
1. Founder’s Effect
some individuals of a population colonize a new habitat
2. Bottleneck Effect
few survivors are left to reproduce 21

22. The Bottleneck Effect A direct result of genetic drift
As a result of some random event, several alleles are lost from a population when only a small number of individuals in the population survive to reproduce.
Northern Elephant Seals – pop. reduced to 20 individuals due to hunting in 1890’s.
Pop. rebounded to 30,000 now
Very little genetic variation

23. FOUNDER'S EFFECT:
some individuals of a population colonize a new habitat
ex: Columbus bringing organisms to USA
S. America: DNA Frequency
25% pink
75% red
Spain: DNA Frequency
66% pink
33% red 23

24. HOW DOES GENETIC DRIFT AFFECT THE DIVERSITY OF A POPULATION OVER TIME?24

25. Genetic drift = decrease in DNA diversity
Genetic drift decreases diversity. In this case yellow and pink DNA are gone, and red DNA is now the majority.
Genetic drift = decrease in DNA diversity 25

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

27. Prezygotic Isolating Mechanism #1: Temporal Isolation
Species isolated because they reproduce in different seasons or times of day
Prevents species from ever breeding together – keeps two species separate but usually arises after species have formed.

28. Prezygotic Isolating Mechanism #2: Behavioral Isolation
Species Differ In Their Mating Rituals (e.g. different bird songs, mating colors, dances, pheromones, etc.)

29. Prezygotic Isolating Mechanism #3 Ecological Isolation
Species inhabit the same area, but different habitats, so they don’t encounter each other

30. Prezygotic Isolating Mechanism #4:
Mechanical Isolation
Body structure prevents mating
In layman’s terms - the parts don’t fit
Bush Baby

31. Prezygotic Isolating Mechanism #5
Gametic Isolation
The sperm is unable to fuse with the egg.

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

33. 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