1. Learning Intention: 8.LS4.4
Science
8th Grade
Standard 12
Learning Intention: 8.LS4.4
Develop a scientific explanation about how natural selection effects the survival of a species in changing environments.
Terms to Investigate
natural selection, species, and environment
Cross Cutting Concepts
CCC 02: Cause and Effect,
CCC 06: Structure and Function
CCC 07: Stability and Change
Success Criteria/I Can Statement
By the end of this unit I will be able to say...
...I can explain the connection between natural selection and
species survival.

2. Phenotype Variation in Populations
Variation refers to a variety or diversity of traits
(different kinds) within any given population.
Two causes of variation
1) Diversity of genetic traits from sexual reproduction.
2) Diversity of genetic traits that result from mutations.
Adapt or Die
Environments always change, sooner or later.
Organisms must adapt to these changes or die.
If too many individuals die, then the species goes extinct.
Those that survive pass on their DNA to their offspring.
When an environmental change occurs, a variety of traits within a population provides the species a chance that at least some individuals will survive the changed conditions.

3. Four Phases of Natural Selection
Bunny Rabbits
Overproduction
Too many offspring are born.
Phase 1
Genetic Variation in a Population
Offspring are born with a variety of traits. Some offspring are better suited to survive than others.
Phase 2
Genetic Variation in a Population
Offspring are born with a variety of traits. Some offspring are better suited to survive than others.
Struggle to Survive
Offspring compete for limited resources. Many die or are eaten.
Phase 3
Successful Reproduction
The well-adapted offspring
survive to breed with each other.
Phase 4

4. Genotype Variation in Populations
The Galapagos Islands are located in the Pacific Ocean about 600 miles west of Ecuador (see picture below).
At some point in the past, a small population of Finches (birds) were blown from South American to these islands.
Each island has a slightly different ecosystem, and these finches adapted accordingly. This lead to significant variation in the shapes and sizes of their beaks.
South American Finch
Galapagos Islands
Consists of 18 larger islands
and 3 smaller islands.

5. Food Source Only Bugs Food Source Seeds & Bugs Food Source Only Seeds
Over time the finches developed different beak shapes and sizes in order to eat the local food (structural adaptations).
Food Source
Only Bugs
Food Source
Seeds & Bugs
Food Source
Only Seeds
narrow-pointed beak for insects
Moderately wide beak for cracking seeds and sharp point for insects
Very wide beak for only eating seeds
Natural Selection:
On each island, Finches with the most effective beaks dominated
while those with less effective beaks died out.

6. Activity We will simulate their two food sources
Let’s see how beak variations in a population of birds
enables some to adapt to a specific environment.
A bird species is brought to an island with just 2 food sources.
We will simulate their two food sources
Worms
Seeds
Pieces of Yarn
Popcorn Kernels

7. Activity
For this activity we will simulate the beaks with these 4 items
Large/wide Beak
Medium Beak
Plastic Spoons
Plastic Forks
Small Beak
Large/thin beak
Plastic Knives
Popsicle Sticks

8. Activity Food Resources Represented by Calories Worms Pieces of Yarn
You will be given simulated bird beaks and bird food.
You will have only a brief amount of time to eat your food.
You will record your data using info from these 2 tables.
Food Resources
Represented by
Calories
Worms
Pieces of Yarn 10
Seeds
Popcorn Kernels 3
Food Intake
To Survive
To Reproduce
30 calories
50 calories

9. Activity Instructions
Each group of four students will have the following items:
1) A plate with food: yarn (worms) & popcorn kernels (seeds)
2) Pair of plastic spoons: (Large/wide beak)
3) Pair of plastic forks: (Medium beak)
4) Pair of plastic knives: (Small beak)
5) Pair of popsicle sticks: (Large/thin beak)
6) Four bowls (one for each student)
Step 1: Select a bird beak type.
Step 2: When signaled by the teacher, use your beak to “eat” for 45 seconds. Place your “eaten” food in your bowl.
Step 3: Determine the number of calories that you “ate.”
Step 4: Determine if your bird survived and/or reproduced.
NOTE: Record details in your science journal.

10. Activity Results What bird beak did you have? (Circle One)
Large/wide Beak
Medium Beak
Small Beak
What bird beak did you have? (Circle One)
plastic spoons: (Large/wide beak) plastic forks: (Medium beak) plastic knives: (Small beak) popsicle sticks: (Large/thin beak)
Season
(45 sec each)
Calories
Consumed
Survive
(Yes or No)
Reproduce
One
Two
Three
Four
Was your bird’s phenotype well suited for survival in this ecosystem? (Explain why or why not)

11. 8.LS4.3 Analyze...anatomical evidence that demonstrates that specific phenotypes in a population can increase survival rates.
(1) What anatomical (phenotype) differences did these finches have?
(2) Which phenotype was best suited for this island environment?
(3) Which phenotype was the least suited for this environment?
(4) How did phenotype variations enable this species to survive?
8.LS4.4 Develop an explanation about how natural selection effects the survival of species in changing environments.
(5) Describe how the Finches went through the four phases of
natural selection.
Phase 1-Overproduction:
Phase 2-Offspring Variation:
Phase 3-Struggle to Survive:
Phase 4-Reproduction:

12. Review Questions

13. Review Questions

14. Review Questions

15. Review Questions

16. Review Questions