1. 7B Natural Selection
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2. Everyone has heard of Darwin and natural selection, but what does it really mean?

4. Natural Selection: Must have FOUR factors
1. A species must be able to increase in number
The organisms must be able to reproduce and pass their genetics on to the next generation
*in nature organisms often produce more offspring than can survive

5. Natural Selection: Must have FOUR factors
2. The heritable genetic variation is due to mutations and sexual reproduction There must be variation in the traits. Can come from mutations or sexual reproduction. The offspring can be different from the parents

6. Natural Selection: Must have FOUR factors
3. Competition for limited resources
If there is competition, then some traits will make organisms better suited to survive. Better able to feed. Better able to fight. Etc. “Survival of the Fittest”
*fitness means ability to survive

7. Natural Selection: Must have FOUR factors
4. The offspring of those organisms that are the “fittest” will be better able to survive and reproduce The offspring of the fittest, will also be the fittest. They will survive better and pass on the traits generation after generation

8. Adaptations
If there is one trait that helps an organism survive and it is passed down from generation to generation, what will happen to the population over time?
More individuals will have that trait
The resulting trait is called an adaptation

9. What are some things that could help natural selection occur?
Biotic factors
Introduction of a new species
Abiotic factors
Seasonal temperature ranges
Long-term climate change
Acidity
Light
Geographic barriers

10. Environmental Changes
Deforestation
Fishing
Fertilizer application
Drought
Flood
Rate of change of the environment can affect the distribution or disappearance of traits in species

11. Death of Your Lake Activity

12. Types of Natural Selection

13. Directional Selection

14. Directional Selection
What could cause this type of selection?

15. Stabilizing Selection

16. Stabilizing Selection
Why would this be better?

17. Disruptive Selection

19. Long Term Effects of Environmental Changes
Some species may grow and flourish
Emergence of a new species (speciation)
Extinction of a species

20. Over many generations…
With biotic and abiotic pressures, over time adaptations occur
You can from your parents  grandparents  great grandparents  great great grandparents  etc, etc, etc
We all come from descendants
Darwin argued that we are all descendants with modification
We all possess adaptations that have occurred over time