1. Unit 9: Evolution
9.4 How Evolution Happens

2. Species
A species is a populations whose members can interbreed and produce fertile offspring
Speciation: The formation of new species through evolution
Example Darwin’s Finches

4. How Evolution Happens
Mutation
Isolation
Sexual Selection

5. Mutations Changes in the DNA that may change a trait in an organism.
Some mutations go unnoticed…not all changes in DNA impact survival.
Some mutations are negative…and can be fatal.
Some mutations are beneficial…and may lead to changes in a population over time through natural selection.

6. Isolation Geographic/ habitat isolation
Live in different habitats, rarely see each other
Figure 24.6
A. harrisi
A. leucurus

7. Isolation Temporal Isolation
Two species breed during different times of the day, different seasons or different years.
These two related frog species exhibit temporal reproductive isolation. (a) Rana aurora breeds earlier in the year than (b) Rana boylii.

8. Isolation Behavioral Isolation
Special signals attract mates, elaborate behaviors attract mates

9. Isolation Reproductive Isolation
Is the existence of biological factors that impede members of two species from producing viable, fertile hybrids
Sperm of one species, not able to survive in female of other species

10. Isolation Mechanical Isolation
They can try, but are anatomically incompatible.

11. Sexual Selection
Mating choices can change the composition of a population over time. “Survival of the sexiest”
In this case traits DO NOT help an organism survive in a particular environment, but rather help an organism find a mate!
                                                   
                                                   

12. Sexual Selection – 2 methods
Female Choice—females selecting males for their “attractiveness”
Male-Male Competition—males competing with males for females
Note: there are exceptions to this based on species
Who to choose?
She’s mine!

13. Costs of Sexual Selection
Many organisms expend a lot of energy to get mates:
Large showy tails in peacocks
Seals fight for territories
Males build large, showy nests
Some organisms have features to attract mates but are harmful to their survival: (i.e., also attract predators)
Large antlers of moose
Bright coloration in cardinals
Long tail feathers in pheasants

14. Benefits of Sexual Selection
For Males:
Get to pass along their genes!
For Females:
The chance of bearing offspring that will survive and also reproduce.
Parental help
Good territory
**All Benefits Ensure Greater
Survival of the Offspring!!**
A brightly colored male, might, for example, be better and providing food or be less likely to have a disease that would be transmitted to the female or the offspring.
It may be that the female receives no direct benefits from mating with a high quality male, but the male may have high genetic quality so that if a female mates with a high quality male her offspring will inherit the alleles for high quality. A female who mates with a male with high genetic quality should therefore have more surviving offspring.

15. 3 Types of Natural Selection
Natural selection can affect the relative fitness of phenotypes producing 3 different types:
Directional Selection
Stabilizing Selection
Disruptive Selection

16. Directional Selection
Directional Selection: When individuals at one end of the curve have higher fitness.
Usually happens when the environment changes or a species moves to a new location.
Example: Size and shape of finch beaks based on the availability of certain seeds.

17. Stabilizing Selection
Stabilizing Selection: When individuals near the center of the curve have higher fitness than individuals at either end
Example: Birth weight in human babies

18. Disruptive Selection
Disruptive Selection: When individuals at the outer ends of the curve have higher fitness than individuals near the middle of the curve
Example: Birds with small and large beak sizes with nothing in the middle

19. Patterns of Evolution
Convergent Evolution: the process whereby organisms not closely related independently evolve similar traits as a result of having to adapt to similar environments or ecological niches
Example: similar nature of flight/wings of insects, birds, pterosaurs, and bats
Results in analogous structures

20. Patterns of Evolution
Divergent Evolution: the process whereby organisms that are closely related species split into two or more different species.
Example: Darwin’s finches- 15 species diverged from a single species of finch that arrived on the Galapagos islands
Results in homologous structures