1. Natural Selection
The process whereby organisms better adapted (fit) to their environment tend to survive and produce more offspring
Organisms NOT fit die off, eventually resulting in extinction
“Environmental pressures” like lack of food due to competition, predation, or disease cause natural selection

2. What does “fit” for an environment mean?

3. “Fitness”
The ability of an organism to survive and REPRODUCE in ITS UNIQUE ENVIRONMENT
Fitness looks different depending on the environment!

4. Natural Selection: How’s it work?
There is competition among living things
More are born or hatched or whatever, than can survive and reproduce
Reproduction occurs with variation
This variation inherited by the offspring

5. How’s it Work?
Selection Determines which individuals enter the adult breeding population
This selection is done by the environment
Those which are best suited reproduce
They pass these well suited characteristics on to their young

6. How’s it Work? REPRODUCTION is the key, not merely survival
If you survive to be 128 but have no kids, you are not doing as well as the man who dies at 35 and has a son
Assuming his traits that made him successful will help his son then he is more fit NOW than the 128 year old guy

7. Mutations
Random mutations can create new alleles in a group of organisms
Gene versions

8. Allele – Review! Alleles are gene versions!
We all have a gene for eye color – but some of us have alleles for blue eyes, some of us have alleles for brown eyes, and others have alleles for other colors.

9. Mutations
Random mutations can create new alleles in a group of organisms
Often go unnoticed, but occasionally mutations help an organism survive and reproduce in environmental pressures
The better mutations an organism has, the more “fit” it is
Gene versions

10. Example coming… Ever heard of antibacterial soap?
What about bacterial resistance to antibacterial soap?

11. How natural selection works
Resistance to antibacterial soap
Generation 1: not resistant
resistant

12. Resistance to antibacterial soap
How natural selection works
Resistance to antibacterial soap
Generation 1: not resistant
resistant

13. Resistance to antibacterial soap
How natural selection works
Resistance to antibacterial soap
Generation 1: not resistant
resistant
Generation 2: not resistant
resistant
mutation!

14. Resistance to antibacterial soap
How natural selection works
Resistance to antibacterial soap
Generation 1: not resistant
resistant
Generation 2: not resistant
resistant
Generation 3: not resistant
resistant

15. Resistance to antibacterial soap
How natural selection works
Resistance to antibacterial soap
Generation 1: not resistant
resistant
Generation 2: not resistant
resistant
Generation 3: not resistant
resistant
Generation 4: not resistant
resistant

16. Antibacterial resistance 
The bacteria underwent mutations that allowed them to survive better in their environment, allowing them to reproduce.
Eventually the majority of bacteria had the trait for resistance!

17. Adaptations
Mutations that are “fit” for a specific environment

18. How Do Mutations Make An Organism More “Fit?”
1) Help the organism better obtain food

19. 2) Help the organism better protect itself from predation, disease or the environment it lives in

20. 3) Help the organism better attract mates

21. Evolution of Populations
For Example: The Galapagos Tortoises
When Darwin sailed to the Galapagos Islands he saw a lot of adaptations.

22. Evolution of Populations
Each tortoise was found on their own island and each was best suited for the vegetation on that island
Short necked - adapted to eating food low to the ground
Medium necked - adapted to being able to eat both from the ground and higher up
Long necked - adapted to being able to eat food higher up

23. Natural selection can cause
populations to diverge as they prefer certain environments.
north
south
divergence
Divergence can lead to new species.

24. Exit Ticket
1. What determines whether the frequency of a mutation will increase or decrease in the gene pool of a species?
2. In a forest, the color of tree bark gradually darkens over many years due to industrial pollution. A population of light-colored insects hides from predators during the day on the tree trunks. Which effect would the change in tree color most likely have on a dark-colored gene in the insect population?
A  Mutations will be more likely to produce the dark-colored gene.
B  The dark-colored gene will shift from recessive to dominant.
C  The frequency of the dark-colored gene will rise in the population.
D  Offspring will be more likely to inherit the dark-colored gene if one of their parents has the gene.