The Orange Circle Theory (Day #2 of 3)

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1. Construct an explanation based on the evidence that the process of evolution primarily results from four factors, including reproductive potential, heritable variation, scarcity of resources, and survival of the fittest. (HS-LS4-2) 2. Construct an explanation based on evidence for how natural selection leads to adaptation of populations. (HS-LS4-4)

Big Idea

The Theory of Natural Selection can be thought of an on-going cycle whereby generations of populations encounter an ever changing environment that selects winners and losers. To the winners go the spoils!

Learner Goals

Note: I recommend that you first check out this resource in order to get the most out of this lesson!

In high school I took several drafting classes and, for a while, I had hoped to become an architect. With respect to planning instruction and teaching, I feel that I can still live out the detailed approach to building something intricate and complex even though the product is a lesson rather than a certain "built environment".

The lesson-planning document that I uploaded to this section is a comprehensive overview of how I approach lesson planning. This template includes the "Big Three" aspects of the NGSS standards: Disciplinary Core Ideas, Crosscutting Concepts, and Science Practices. Of course, there are many other worthy learning goals, skills, instructional strategies, and assessments that can be integrated into a class session. I don't feel compelled to check every box but, rather, use it as a guide to consider various options and tailor the lesson in light of these.

With regard to this particular lesson...

1. students will construct an explanation based on the evidence that the process of evolution primarily results from four factors (HS-LS4-2):

  • the potential for a species increase in number
  • the heritable genetic variation of individuals in a species due to mutation and sexual reproduction
  • competition for limited resources, and
  • the proliferation of those organisms that are better able to survive and reproduce in an environment

 2. students will construct an explanation based on evidence for how natural selection leads to adaptation of populations, including effect(s) of changing biotic and abiotic conditions on resulting in changing adaptations among members of a population. (HS-LS4-4)

I hope you get some value from my work! Please find the more intricate details of this lesson plan there.

Anticipatory Set ("Hook")

5 minutes

Please click here for the previous lesson in the series.

Because sometimes, those kids just forget what they learned...

Turn & Talk- What does the orange circle symbolize? Identify three ways it can be used as a mental model for Natural Selection.

Sample responses might include:

1. "The circle represents a generation in the life of a population."

2. "The steps along the circle (starting with "variation") shows the series of events that has to happen for a species to survive."

3. "It is like the circle of life!" (typical Lion King response)

Instructional Input/Student Activities

45 minutes

Necessarily, my instructional plan accounted for several key hurdles that students will need to encounter and overcome:

1. How do I make sense of a really abstract idea (Theories in general and Natural Selection in particular)?

2. What should an argument look like? How do I meld a claim, its evidence, and underlying thinking (reasoning)?

3. What is the evidence brought forward by evolutionary biologists?

4. When looking at nature, how would Darwin explain its patterns and processes?

Teaching Challenge: How do I support my students to compose, communicate, and evaluate a clearly stated, evidence-based argument?

Teaching Challenge: How do I support students to develop and use scientific models?

Mental model of a scientific theory. Lines of evidence. Mental model of Natural Selection.

These scaffolded elements will be necessary to help students walk through the process of explaining, based on evidence, the processes driving Natural Selection. This then is the output of this series built on the combined skills and knowledge leading up to this point. 


Using an interactive lecture strategy, the specific tenets of Natural Selection will be outlined and investigated in turn.

The Theory Lecture (slides #18-33)- Emphasis on these concepts:

  • the nature of “variation” (slide 19): my students will already have learned about genetics and the mechanisms by which new variations are introduced via meiosis and subsequent sexual reproduction. Here is a lab that led students through a portion of this enduring understanding.
  • the nature of “adaptation” (slide 20-22): Lamarckism is a persistent misconception even after more than 150 years of its original demise. Many students bring with them this concept that organisms have control over their fate. One root of this error is the similarity between the term "adapt" (a verb) and "adaptation" (a noun). A sampling of student understanding of adapt can be seen in this "Draw It" lesson (which I reference by showing examples of student work from the class to show how subtly the meanings of "adapt" and "adaptation" can become comingled. I stress that it is the genotype that determines the phenotype and it is the "adaptation" (four syllables) that is phenotypic; wings, claws, blubber, beaks, etc. Just because one might adapt to a cold winter day by donning a North Face jacket, any potential offspring will still be just as cold as the parent (sans North Face).
  • the nature of “selection” (slide 23-24): The various faces of the environment that lead to sustained life or death. One could really expand on this topic in light of recent outbreaks of Ebola, influenza, among the many warm and snuggly pathogens.
  • the nature of “reproduction” (slide 25-28): Based on one's comfort level discussing sex and all its trappings with a class full of teens, this could be a rather short discussion or it could be drawn out. I discuss the practical reasons that organisms (same or different species) cannot successfully breed. This amounts to pre-zygotic barriers (e.g. long distance relationship) or post-zygotic barriers (e.g. hybrid infertility that causes ligers to be sterile, in general).
  • the nature of “speciation” (slide 29-33): A compare and contrast of the two modes of speciation, one involving geographic barriers and the other amounting to little more than "I am not attracted to you even though you are my neighbor".

Closure: What did we learn? Where do we go from here?

5 minutes

Random Draw (True or False)- Ask students comprehension questions related to the topics of study based on the first two days of lecture. This could include:

1. “True or False-Humans evolved directly from chimpanzees.” (False)

2. “True or False-Populations, not individual organisms, evolve over time as their gene pools change due to selection factors.” (True)

3. “True or False-A given adaptation that an organism is born with is the result, in part, of random genetic changes that occur during meiosis.” (True)

Please click here for the next lesson in this series.