2. 15-1 Notes: Adaptations and Natural Selection
Evolution Unit
15-1 Notes: Adaptations and Natural Selection

3. Adaptations
A hereditary characteristic that helps an organism survive and reproduce in its environment.

4. Fitness
Measure of ability to survive and produce more offspring relative to other members of a population

5. Animal Observation

6. So how did these organisms become so well adapted to their environment?

7. Darwin proposed that animals evolved to fit their environments.
Darwin’s Explanation
Darwin proposed that animals evolved to fit their environments.

8. Evolution
The change in a population of organisms over time

9. Darwin’s Explanation
Darwin realized that animals have many offspring and some don’t survive. The survivors are better suited to their environment.

10. He called this process….
Natural Selection

11. Natural Selection
Mechanism by which the environment is the selective agent
Mechanism by which evolution occurs
Darwin said that in nature, environment creates selective pressure

12. Steps of Natural Selection
Overproduction
-organisms have many offspring, but not all will survive.

13. Steps of Natural Selection
2. Genetic Variation --Individuals vary within a population --New traits appear due to genetic mutations

14. Steps of Natural Selection
3. Struggle to Survive --Organisms compete for resources (food, water, shelter, and mates) --Organisms have to get away from predators

15. 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

16. Steps of Natural Selection
4. Descent with Modification --Organisms with the best adaptations will survive and reproduce passing these good traits down to their offspring

17. Natural Selection acts on phenotypes not genotypes As environment changes, different traits will become beneficial.

18. Examples of Natural Selection

19. Insects become resistant to insecticides.
Insecticide kills off most insects.

20. Those insects that survive have a gene that makes them resistant.

21. Resistant insects reproduce with other resistant insects.

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

23. Other examples of evolution:
Bacteria become resistant to antibiotics Don’t take antibiotics unless you have a bacteria infection!

24. Other Examples of Natural Selection:
Peppered Moths in England There were more light moths (on light trees) before There were more dark moths (on light trees) after 1850.