1. 8-5 Notes: Natural Selection

2. SO HOW DID ORGANISMS BECOME SO WELL ADAPTED TO THEIR ENVIRONMENT?

3. DARWIN’S EXPLANATION Darwin proposed that animals evolved to fit their environments.

4. EVOLUTION The change in a population of organisms over time

5. DARWIN’S EXPLANATION Darwin realized that animals have many offspring and some don’t survive. The survivors are better suited to their environment.

6. HE CALLED THIS PROCESS….

7. NATURAL SELECTION Mechanism by which EVOLUTION occurs The environment is the selective agent Darwin said that in nature, environment creates selective pressure

8. STEPS OF NATURAL SELECTION 1.Overproduction -organisms have many offspring, but not all will survive.

9. STEPS OF NATURAL SELECTION 2. Genetic Variation Individuals vary within a population

10. STEPS OF NATURAL SELECTION 2. Genetic Variation Individuals vary within a population New traits appear due to genetic mutations

11. STEPS OF NATURAL SELECTION 3. Struggle to Survive Organisms compete for resources (food, water, shelter, and mates) Organisms have to get away from predators

12. STEPS OF NATURAL SELECTION 3. Struggle to Survive Some adaptations allow organism to survive at higher rate and individuals are “naturally selected” to survive and produce offspring

13. STEPS OF NATURAL SELECTION 4. Descent with Modification Organisms with the best adaptations will survive and reproduce passing these beneficial traits down to their offspring

14. Natural Selection acts on PHENOTYPES (traits) not genotypes

15. As environment changes, different traits will become beneficial.

16. EXAMPLES OF NATURAL SELECTION

17. INSECTS BECOME RESISTANT TO INSECTICIDES. 1. Insecticide kills off most insects.

18. 2. Those insects that survive have a gene that makes them resistant.

19. 3. Resistant insects reproduce with other resistant insects.

20. 4. Their offspring have the resistant gene. Insecticides don’t work very well over time!

21. OTHER EXAMPLES OF EVOLUTION: Bacteria become resistant to antibiotics Don’t take antibiotics unless you have a bacteria infection!

22. OTHER EXAMPLES OF NATURAL SELECTION: Peppered Moths in England There were more light moths (on light trees) before 1850.

23. OTHER EXAMPLES OF NATURAL SELECTION: Peppered Moths in England There were more dark moths (on dark trees) after 1850.