1. Darwin and Natural Selection
Intro: Why does evolution matter now?
CHARLES DARWIN

2. Discuss with a Partner
What do you think biological evolution is? Do you have any opinions about it?
What do you think natural selection is? How do you think it works?

3. The voyage of the HMS Beagle
1831, when Darwin was 22 years old

4. The Galapagos Islands and Darwin’s Finches
Short video about Darwin’s finches
Intro (describes Darwin’s voyage) and 10:54 of “Unlocking the Mysteries of life” (shows finches feeding)

5. Natural Selection: Darwin’s idea
In nature, organisms produce more offspring than can survive.
This results in a struggle for survival
Example: Fishes
A single female cod can lay millions of eggs
Atlantic cod

6. Variation exists in all populations
Note: variation is heritable (genetic)
Example:
fish differ in
color,
size and
speed

7. 3. Individuals with useful variations survive and pass those traits (alleles) on to their offspring.
Any useful variation that helps an organism to survive and reproduce is called an adaptation.
Example: fast fish escape predators, survive and produce more fast fish.

8. 4. Over time, organisms with certain variations become the majority and the population may look very different from the ancestral population

9. Natural Selection (summary)
The environment acts on variations in a population, causing genetic change over time.

10. Watch the video and compare the concepts to your notes

11. Quick Activity! Questions!
Choose a number between 1 and 4 (show with fingers)
Simulate natural selection by adding antibiotic to kill off those who are less resistant (by number)
Allow survivors to reproduce (pick dead neighbor to be like them).
Questions!
Explain how the activity illustrates natural selection in your assignments notebook!
Create your own example of natural selection and explain it!
If you lift weights and get really strong, will your kids be really strong and therefore more likely to survive? Explain your answer.

12. There are three types of Natural Selection:
Stabilizing Selection
Directional Selection
Disruptive Selection

13. Stabilizing Selection
Type of selection in which…
average individuals are favored (selected for)
Extreme forms of a trait are selected against.

14. Example of Stabilizing Selection: Spiders
Large spiders are easily seen and eaten by birds
Small spiders can’t compete for food
Medium size spiders are selected for

15. Directional Selection
Type of selection in which…
one extreme form of a trait is favored (selected for).

16. Example of Directional Selection: Woodpeckers
A type of insect lives
deep within the bark of
trees
Woodpeckers with short
or average-size beaks
can’t get to these insects
Long-beaked
woodpeckers are
selected for

17. Disruptive Selection Type of selection in which…
BOTH extreme forms of a trait are favored (selected for)
Average individuals are selected against.

18. Example of Disruptive Selection: Limpets
Limpets are snails
that live attached to
rocks in the tidepools
Limpets range in
color from white to tan
to dark brown
White colored limpets
have the advantage on
light-colored rocks
Dark brown limpets
dark-colored rocks

19. Which type of natural selection is shown in each graph?1 2 3

20. How is Natural Selection related to Evolution?
It is an important mechanism by which evolution occurs

21. Check your understanding
For each of the following examples, tell me which type of selection it would be.
Imagine a population of mice living at the beach where there is light-colored sand interspersed with patches of tall grass. Light-colored mice blend in with the sand and dark-colored can hide in the grass. Medium-colored mice would not blend in with either the grass or the sand and, thus, would more probably be eaten by predators.
If thicker-shelled oysters are more resistant to breakage than thinner-shelled oysters, crabs will be less able to prey upon them, and thicker-shelled oysters will be more likely to survive to reproduce.
Most robins lay 4 eggs. Larger clutch sizes result in malnourished chicks, while smaller clutch sizes may result in no viable offspring surviving.

22. For the following videos, determine which type of natural selection is occuring. Justify your conclusion.
HIV and Natural Selection
skip first 35 seconds (Evolution and AIDS)
Toxic Newts: