Natural Selection - Survival of the Fittest

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Objective

SWBAT to explain the true meaning of the phrase "Survival of the Fittest"

Big Idea

Students explore the process of natural selection.

Engage

5 minutes

To engage students in this lesson I conduct a formative assessment probe that elicits students' ideas about natural selection.  Specifically I want to see what the common phrase, "survival of the fittest" means to my students.  

One of the most common misconceptions in evolution is this phrase.  To many this implies that only the strongest are the individuals "selected" to survive.  This probe is useful because it provides me with valuable information on misconceptions that my students may have.

The probe "Is it "Fitter"?"  is one of many terrific probes found in a series of books published by the NSTA. Even if you don't have access to the probe, asking students to think, or do a quick write, or think-pair-share on the meaning of the phrase "survival of the fittest" will probably give you enough information.   

The best answer is Lance's:  "I think "fit" means more apt to reproduce."  Even though traits such as speed, intelligence, and strength might lead to survival, they don't guarantee successful reproduction.  The true definition for fitness in an evolutionary sense is being able to pass one's genes to a next generation (reproduction). The peppered moth lesson done prior to this one is a great example. The "strongest" moth isn't the most likely to survive - the moth that can best blend into its surroundings is the most likely to survive. (MS-LS4-4. Construct an explanation based on evidence that describes how genetic variations of traits in a population increase some individuals’ probability of surviving and reproducing in a specific environment.) 

* Uncovering Student Ideas in Science (Volume 4)- 25 NEW Formative Assessment Probes by Page Keeley and Joyce Tugel (2009).

Explore

25 minutes

In this section of lesson students explore the process of natural selection by conducting a Bird Beak Natural Selection Lab. (SP2 - Developing and Using Models)

In this lab students conduct a scientific investigation (Question, Hypothesis, Data Analysis, Conclusion) to answer the following question:

"How does the shape of a bird's beak affect how it survives?" 

Materials:

  • Bird Food - Spaghetti, Macaroni, Rubber Bands, Rice
  • Beaks - Spoon, Clothes Pin, Chopsticks, Fork
  • Cup 
  • Timer

Procedure:

  1. Students work in groups of four (each students get his/her own "beak").
  2. Place bowl of food in front of each student.
  3. At the start of the timer each student "bird" has 15 seconds to eat.
  4. At the end of each time, each student counts how many particles of food it has eaten and record on data table.
  5. Each student passes food to person clockwise and repeats steps 2 through 4.

Data Analysis: (SP4-Analyzing and Interpreting Data) 

Once students have recorded their data, they analyze it to come up with a conclusion where they state if their hypothesis was right or wrong.  In particular, it's important to focus on the following question:

"How does the shape of a bird's beak affect how it survives?"    

It's important for students to understand that the trait "birds' beak type" only can be considered an adaptation if it allows for survival and eventual reproduction (i.e. natural selection).  This is a good part in lesson to go back to the probe and emphasize that "fitness" involves successful reproduction. (MS-LS4-4. Construct an explanation based on evidence that describes how genetic variations of traits in a population increase some individuals’ probability of surviving and reproducing in a specific environment.) 

Explain

15 minutes

In this section of lesson students read an article on Natural Selection from cK-12.  

Topics Covered:

1.  Inherited vs Acquired Traits

2.  Adaptations

To check for understanding, students answer the following questions at end of video:

  1. What's the difference between an acquired and inherited trait?
  2. Define natural selection.
  3. What is an adaptation?
  4. What is required for natural selection to take place?
  5. How many species are there on the planet?

In addition to reading, I show students Evolution in 1 Minute video that does a good job at visually summarizing the process of natural selection.  

It's important to point out to student that genetic variation, along with environment conditions, produces the conditions for natural selection.  

In addition, it's crucial to communicate the fact that natural selection is not an active process, meaning nature is not intentionally selecting one set of individuals over others.  Once again "Survival of the Fittest" requires successful reproduction. (CCC - Cause and Effect)

Elaborate

10 minutes

Students now elaborate on what they have learned by playing Charles Darwin's Game of Survival courtesy of the Science Channel. 

Objective of interactive demo is for students to see that environmental conditions are the driving force in determining what individuals are able to survive and reproduce.  Genetic variation is important for a species to survive under changing environmental conditions.  The game also demonstrates that traits such as being tall or strong doesn't always guarantee survival.

Activities on Site:

1.  Learn about Natural Selection

  • Genetic Variation
  • Passing of Traits
  • "Survival of the Fittest"

2.  Survival Game

  • In this game students need to create a species that will be able to survive changing environments.

3.  Natural Selection Quiz

4.  Darwin's Bio

5.  Glossary

Evaluate

5 minutes

Now students write an evidence based argument. They are expected to explain the true meaning of the phrase "survival of the fittest", citing evidence from the lessons activities (i.e. bird beak lab, reading, natural selection simulation) to support their claim and their reasoning. (SP7 - Engaging in Argument from Evidence/WHST7.1 - Write arguments to support claims with clear reasons and relevant evidence.)