Observing Variation

At the end of this lesson students will be able to:

1. identify patterns of similarities and differences in traits shared between specimens.
2. create a scientific sketch that communicates information that can be used by other scientists.
3. construct an explanation for how an individuals’ variation might effect the survival of a larger population.

• make copies of the student field journal (1 per student)
• gather several specimens of the same species (1 per student)

Teacher Tip: You can choose whatever type of specimen that you like, but they should all come from the same species. We’ve used a variety of types of specimens from leaves to peanuts to oranges to sea shells. Make sure that whatever specimens you are collecting for this activity, have been collected in a sustainable manner.

1. Select as many specimens of the same species as there are students and place them in a central location.
    
2. Explain that these are specimens of a single species.
    
3. Let all students examine all specimens. Ask them to look for variation.
    
4. Ask each student to select a specimen.
    
5. Pass out the student field journals and tell students to sketch their specimen. Encourage students to measure the specimen and add any descriptive notes that will help them identify their specimen.
    
6. When they have finished the field journal, have small groups (5 to 8 students) mix their specimens up and try to find them again based on their sketches.
    
7. Have students reflect on what parts of the sketch helped them identify their specimen. Then, give them a chance to add a few more details to their sketch.
    
8. Mix the specimens back together again, and have students switch sketches with a classmate. Can someone who didn’t observe the same specimen identify it based on the sketch and notes of the first student?
   • Teacher Tip: This emphasizes the importance of acute observation and detailed documentation, especially when other scientists will be using your work.
      
9. Have students reflect on what they think a good scientific journal entry would entail. Ask questions such as: What observations were particularly useful in finding your specimen or your classmate’s specimen? What other details, words or measurements could have made it easier to find the correct specimen? How does sketching vs. taking a picture help you notice the details of a specimen?

“Variation fuels the process of evolution. No two individuals of any species are exactly alike. Even if they look similar, differences in their genes distinguish one from the other. While subtle, those differences may allow some to live longer and produce more offspring than others. That process – called natural selection – drives evolution.” – California Academy of Sciences exhibit text.

Variation is a fundamental prerequisite in order for evolution to occur. To see natural variation, all you have to do is look around you. Human beings, as with all species, exhibit a range of natural variation that is visible. We have different shaped faces, different eye colors, different skin colors, and much more. We also have variations that are not visible in our appearance, yet they are observable, such as human blood type.

These natural variations within a single species arise for a variety of reasons. One major reason that organisms who reproduce sexually have variation is because each individual has a different combination of genes inherited from their parents. But, there is still some variation in variation as is clearly evident in siblings who have the same parents but inherit different genes making them genetically different from one another.

In addition to genetic variation resulting from parents, other causes of genetic variation include the movement of genes from one population to another (gene flow), and changes in the DNA (mutations), which are constantly arising within natural populations.

Furthermore, variation can be a result of different environmental factors. For example, an animal that has access to larger prey may grow larger, while an animal that has only access to smaller prey may not grow as big.

In this activity - Observing Variation – students will observe variation within a single species. Practicing observation is an important scientific skill. After all, Darwin’s observation of variation within and between species was the initial step in his development of the theory of evolution by natural selection.

The items listed below indicate how the activities support the three dimensions of the Next Generation Science Standards:

• Science & Engineering Practices
  • Models
    • K-2: Use and share pictures, drawings, and/or writings of observations.
  • Constructing Explanations
    • 3-5 Use evidence (e.g., measurements, observations, patterns) to construct or support an explanation or design a solution to a problem.
    • Identify the evidence that supports particular points in an explanation.
• Disciplinary Core Ideas
  • 1.LS3.B: Variation of Traits. Individuals of the same kind of plant or animal are recognizable as similar but can also vary in many ways. (1-LS3-1)
  • 3.LS3.B: Variations of Traits. Different organisms vary in how they look and function because they have different inherited information.
• Crosscutting Concepts
  • K-2: Patterns in the natural and human designed world can be observed, used to describe phenomena, and used as evidence
  • 3-5: Similarities and differences in patterns can be used to sort and classify natural phenomena.
  • 6-8 Patterns can be used to identify cause and effect relationships.

Butterfly Conservation (2015). Peppered Moth and natural Selection. Retrieved March 25, 2015 www.mothscount.org/text/63/peppered_moth_and_natural_selection.html

California Academy of Sciences. (2008). “Evolving Story”, exhibit text.

Coolidge-Stolz, E., Cronkite, D., Jenner, J., Pasachoff, J. M., & Wysession, M. (2008). California: Focus on life science. Boston: Pearson Prentice Hall.