1. The Theory of Natural Selection

2. Artificial Selection
Defined: Humans select (not naturally) traits thought to be advantageous
Humans created diversity choosing specific traits to breed
Dogs, Crops, Livestock
Only heritable traits can be passed down
Importance: Shows life can change over a period of time

3. Dog traits have been selected by breeders for centuries to produce various breeds.

4. Plants have been bred to produce certain traits for human use also!

5. Natural Selection Four factors:
With adaptation
Without adaptation
Not all these wildebeest will survive
These kittens have variations
Four factors:
Overpopulation: more offspring are born than can survive
2) Variation: individuals of a population have differences
3) Adaptation: Some variations allow a better chance of survival
4) Descent w/ modification: Over time, those with advantages make up most of the population.

6. Natural selection can act only on traits that already exist
The Myth
The Truth
Natural selection can act only on traits that already exist

7. Which rabbit is best adapted to this environment?
Over time, those not adapted most likely die…that’s natural selection!

8. Which rabbit is best adapted?
Do the dark rabbits turn white? No! They get eaten. (survival of the fittest)

9. Struggle for Survival
Fitness: measure of the ability to survive & produce more offspring
As environments change…
Those with adaptation: more likely to survive & reproduce
Those without adaptation: more likely to perish
Populations do not grow unchecked
Limiting Factors: food, water, shelter, disease, predators

10. Sexual Selection Defined: a trait that increases mating success.
Ex: Bright coloring or large antlers
There are two types:
Intrasexual selection: competition among males
Intersexual selection: males display certain traits to females
Mating can have an important effect on the evolution of a population
Occurs due to higher cost of reproduction for females.
Males produce many sperm continuously
Females are limited in the number of offspring they can produce

11. Review What is artificial selection? What is natural selection?
How does natural selection lead to population changes?
Why don’t populations (such as deer) continue to grow unchecked?
Compare the two different types of sexual selection.