2. The Theory of Natural Selection

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

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

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

6. Four factors: 1) 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: Those with advantages will reproduce More of the population will have the advantage Not all these wildebeest will survive These kittens have variations

7. The Myth

8. Natural selection can act only on traits that already exist. Structures take on new functions in addition to their original function. wrist bone five digits

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

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

11. Struggle for Survival Populations do not grow unchecked – Limiting Factors: food, water, shelter, disease, predators Fitness: measure of the ability to survive & produce more offspring

12. Natural and artificial selection are not the only factors in evolution. We’ve learned about natural selection and artificial selection, but what about sexual selection? – Mating can have an important effect on the evolution of a population.

13. Sexual selection occurs when certain traits increase mating success. Sexual selection occurs due to higher cost of reproduction for females. – males produce many sperm continuously – females are more limited in potential offspring each cycle

14. There are two types of sexual selection. –intrasexual selection: competition among males –intersexual selection: males display certain traits to females

15. Natural Selection in Action: The Peppered Moth Analysis Before the industrial revolution, the trees in the forest around Manchester, England were a light grey/green due to the color of lichens (fungus) on their trunks. Peppered moths, or Biston betularia, which lived in the area, were mostly lightly colored with dark spots. However, there was some color variation between the moths. The most common moth color was light with dark spots and the least common were dark with light spots. Because there were not enough resources to support the entire population, the members of this species had to compete for survival. Their coloring, when against a similar background, served as camouflage against predators such as birds and lizards, thus increasing chances of survival.

16. Natural Selection in Action: The Peppered Moth Analysis As the Industrial Revolution progressed, the trees became covered with sulfur dioxide, turning the trunks dark.