Evolution, part 2

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Objective

Students will be able to explain how fossil, biochemical and other evidence support the theory of evolution.

Big Idea

The theory of evolution is supported by real evidence that cannot be discounted.

Warm-Up

5 minutes

Warm-Up: How would you define “fitness” within the context of the theory of natural selection?

This question allows students to activate prior knowledge about evolution from the previous lesson, Evolution, part 1. Look for students to identify that fitness is a measure of how well an organism is suited for its environment.

Display Page Keeley’s Life Science probe, Habitat Change. Ask a student volunteer to read the scenario aloud. Ask students to write the letter choice of the answer they think tells what happens to the divos on a slip of paper. Make sure that students also include an explanation to support their answer choice.  

Following the warm-up question with this quick assessment allows for an assessment of how well students learned the previous content and how well students can take immediate information and apply it to a different scenario. Have students pass their slips to another student, either in front of them or behind them.

Randomly call on students to read the response on the slip they received. Listen for and correct any lingering misconceptions that arise. Be prepared to initiate a quick review of evolution key points.

Introduce New Material

20 minutes

Inform students of the learning target:

  • I can explain how fossil evidence, comparative bone analysis, and biochemical evidence support the theory of evolution.

Introduce the vocabulary associated with the lesson: comparative anatomy, vestigial structure, homologous structure, comparative embryology, analogous structures, derived traits, ancestral traits, and morphology. Plan to explicitly teach the vocabulary associated with the lesson at the appropriate times within the lesson. Make sure that students add the bolded terms to their vocabulary maps as has been practiced throughout the year for terms that have Greek or Latin root words, prefixes or suffixes.

Begin instruction with the video,"What Darwin Never Knew".

Distribute a set of questions for students to complete as they watch the video. This is a long video that can be modified to a shorter viewing segment. The question sheet indicates the times in the video where a particular question is asked. Question 18 from the question set is a good place to start in the video clip (65:10) and follow until the video ends (76:43). This shortened 10 minute segment is most relevant to today’s lesson and sets the stage for students’ understanding that there is real evidence that organisms likely evolved from common ancestors.

Follow the video segment with instruction, using guided notes or use a note-taking format that has been taught. Spend time discussing the pieces of evidence that make the theory of evolution more likely. Use visual aids to help students understand homologous and analogous structures, vestigial structures and comparative embryology.

Check for Understanding by displaying a question prompt for students:

If the cytochrome c of the rhesus monkey is identical to that of humans except for one amino acid, whereas yeast cytochrome c differs from that of humans at 44 positions, which organism is most likely to have evolved from a common ancestor with humans?

Engage students in a brief discussion to gain a sense of their understanding. If necessary, spiral back and re-teach concepts before moving forward.

Guided Practice

10 minutes

Display and distribute copies of an amino acid sequences activity. Ask a student volunteer to read the discussion portion of the activity. The narrative of this activity is rich with academic vocabulary. In order to help students build their academic literacy, make sure that they are able to pronounce the terms correctly. As a rule, I have students repeat new or complex terms after me and clap out the syllables as we pronounce the term together.

Use an interactive pad to model how to complete Data Table 1 using the information from Figure 1.   

Note: Make sure that students first understand the orientation of the data in Figure 1. If not, some students won’t see that the table compares the sequence of amino acids for a human, chimpanzee, gorilla, rhesus monkey horse and kangaroo, from point 87-116 in the amino acid sequence.

First, distribute colored pencils, markers and highlighters to students. Using the think aloud strategy, model how to use the Figure 1 information to complete the data table for humans and chimpanzees and tell students to follow along, making sure to mark any places in the comparative sequences where the amino acids are different from the human sequence, as shown in student work 2 where the student used a blue colored pencil to mark the points where the sequence is different. 

The think aloud strategy is effective because it shows students how to think in order to use the Figure 1 correctly.


Think aloud script:

For example, if I use the table to compare the amino acid sequence for a human and a chimpanzee, I see that they have the same amino acid sequence THR-LEU- SER-GLU-LEU-HIS-CYS for all of the points in the chain from 8-116.  So, I will mark each point in the sequence where there is a difference.  Then, I will count how many places I marked a difference and write the number of amino acid differences I counted in the column labeled, "# of Amino Acid Differences".  

Then, in the column labeled, "Positions in which they vary" I will also write zero because I did not mark any points of difference in the sequence of amino acids for humans compared to chimpanzees.  I know this is correct because I know that vary is a word that means different and there are no differences in the sequence for these two organisms.


Note: Based on your student population, decide if additional modeling is needed to show students how to use Figure 2 and Figure 3 to answer the analysis questions that follow completion of Data Table 1.

Independent Practice

20 minutes

Release students to work in small groups of two to complete Data Table 1 and respond to the Analysis Questions, after analyzing Figures 2 and 3.  

Working in groups of two allows students who are not strong readers to partner with those who are so that the weaker reader will get the support needed to process the reading material, while still able to identify the answers to the questions for themselves.

Encourage students to use active reading techniques such as underlining or highlighting key points or new terms and/or writing questions in the margins to help guide their understanding of this academic text. Provide highlighters and/or different color pens for students' use.

Walk around the room to monitor students as they work. Look for the use of the active reading strategies and encourage those who are not demonstrating the behaviors to do so. Redirect students who appear to be off-track to ensure that all students remain actively engaged in the completion of the assignment. 

Student work 1 is a work product that reflects effective use of the active reading strategies. The student not only highlighted key points, but new terms, as well. The student also wrote questions in the margin that reflected new ideas or thoughts that arose after reading the test. This is an student response that exemplifies active reading. One can assume that this results in the student's ability to correctly complete the data tables and respond meaningfully to the analysis questions.

Student work 2 is a work product that does not reflect use of the active reading strategies.  While most of the answers are correct, some are not correct and there is a noticeable lack of detail in the responses to the analysis questions. One might assume that because the student did not use the active reading strategies, the student missed important details about which table to use to respond to question 3. It is also clear that the student was not able to convey a depth of understanding in constructing responses to the questions since they are not as detailed and complete as the student work 1 responses to the analysis questions.

Close

5 minutes

Distribute post-it notes and instruct students to perform a Square, Triangle, Circle Self- Reflection and respond to each of the following and place them on the chart pad before exiting:

  • What squares with my thinking ( I agree with) is…
  • Three points I learned about evolutionary relationships are…
  • Something that is still circling in my head is…

As a formative assessment, read the student responses and note the following:

What did students agree with about evolution?

Are there any major themes that arise when students indicate three points that they learned?

What topics or questions need to be answered at the first opportunity with students? Are there consistent topics that arise as questions that students still have? If so, review the instruction for gaps that may contribute to students still having questions.

At the first opportunity, summarize the class responses, review the major findings and reteach concepts, as needed.