1. Natural Selection
How species “adapt” to their environment

2. Populations evolve over time, not ________
The fate of individuals ______ evolution
Unfit individuals _________
Fit individuals live and _________
Natural selection promotes survival of __ individuals
They are better suited for the circumstances

3. Natural selection changes “allele __________”
The relative abundance of alleles in a _________
____-evolution: changes in allele frequency in a
population’s gene ____
% of population
Here, the recessive allele
has become rare
Selection increases ________ (“good”) alleles
Decreases maladaptive (“_____”) alleles
New alleles arise through _________
Alteration of the ________ sequence of genes
Causes: radiation, chemicals, replication mistakes
Natural selection ______ if new alleles are adaptive

4. Natural selection can be observed in action
Antibiotic resistance in ________
Pesticide resistance in ________
Color change in _________ moths of Britain
Before Industrial Revolution:
(late 1700s)
Trees covered with white _____
Symbiotic fungus & algae
White moths were camouflaged
Eluded predators
Rare black form got _______

5. After industrial pollution
Coal soot killed ________
Tree bark turned black
White form of moth _________
Got predated, became rare
Black form was better _______
Became the dominant form
Today
Pollution control saved lichen
White form is _____ abundant

6. Artificial selection speeds the process
Animal & plant breeders ______ for certain traits
Choose which individuals will _____
gray wolf
red junglefowl

7. Three trends in natural selection:
 Time 
Neck length
Three trends in natural selection:
1. Directional selection
Results in change toward one _______
E.g., long necks in giraffes
Occurs when environmental change is ___________
Could also lead to increasingly short necks

8. 2. Stabilizing selection
 Time 
Body size
2. Stabilizing selection
Favors an ________ phenotype
E.g., body size in lizards
Smaller individuals can’t defend territory
Larger ones get seen by predators
Occurs in _______ environments

9. Favors ____________over the average Rare
3. Disruptive selection
Favors ____________over the average
Rare
Occurs where 2 types of one _______ are available
E.g., small and large seeds
 Time 
Beak size
Result: ____ bird species can have both
large- and small-beaked individuals
African finch

10. Several “forces” drive natural selection
1. Competition for limited resources
a. _______ species
Individuals with adaptive alleles will win
b. _______ species
E.g., European Starlings vs. Western Bluebirds
Both nest in tree cavities – a limited resource
Starlings are:
- introduced to the U.S.
- larger than native bluebirds
- win the nest hole competition
Bluebirds must _____ or __________

11. 2. Predation
When one organism eats another
E.g., wolves eat deer
Causes biological “___________”
Each side keeps evolving better __________
E.g., deer become _____ and more ____ over time
Because wolves ate the slower, dumber, deer
Wolves become faster over time to catch faster deer
An example of _____________
Two species _________ together

12. 3. Symbiosis
When different species live in _______________
Also coevolution: if one changes, the other _____
a. Parasitism
One species feeds _______ another
Lamprey on salmon

13. One species benefits, the other is __________
b. Commensalism
One species benefits, the other is __________
Some animals commensal with humans:
house sparrow
house fly
European cockroach

14. Both species _________ E.g. ants and swollen-thorn acacias
c. Mutualism
“cleaner fish” on a shark
Both species _________
E.g. ants and swollen-thorn acacias
Acacias provide hollow thorns
Where ants grow “scale insects”
Ants clear away other _______
Acacia has less ________ for water
ant
swollen
thorn

15. Mates are chosen on ____________ of fitness
4. Sexual selection
Mates are chosen on ____________ of fitness
argus pheasants
Female birds mate with males that:
a. Hold good _____________
Ensures a food supply for ________
b. Have “fancy” feathers
Make males ________
Only ____ individuals can risk them
Each generation, males get more colorful
E.g., hummingbirds, peacock
Females remain ______________
Best for ________ on nest.