Making Sense of Natural Selection

Cynthia Passmore, Elizabeth Coleman, Jennifer Horton, Heather Parker
Type Category
Instructional Materials
Article , Unit , Activity
This resource, vetted by NSTA curators, is provided to teachers along with suggested modifications to make it more in line with the vision of the NGSS. While not considered to be “fully aligned,” the resources and expert recommendations provide teachers with concrete examples and expert guidance using the EQuIP rubric to adapted existing resources. Read more here.



This article in NSTA’s September 2013 edition of The Science Teacher describes a unit on natural selection that encompasses eleven 55 minute class periods. A series of activities asks students to explain and make sense of a variety of phenomena, developing their understanding of natural selection over the course of the unit. As a result of engaging in carefully sequenced classroom activities, students make a number of observations and inferences, adding pieces to the natural selection model they are constructing individually and as a class. This unit uses the constructing natural selection model as an anchor for further instruction. Examples of the activities used in the unit include a fish simulation, a sunflower seed activity, and a “worm-eater” game which simulates natural selection, all of which have sense-making discussion components. The unit assessment task asks students to apply what they have learned to explain how the carapaces of different populations of tortoises, found on various islands of the Galapagos islands, changed over time.

Intended Audience

Educational Level
  • High School
Access Restrictions

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Performance Expectations

HS-LS4-2 Construct an explanation based on evidence that the process of evolution primarily results from four factors: (1) the potential for a species to increase in number, (2) the heritable genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for limited resources, and (4) the proliferation of those organisms that are better able to survive and reproduce in the environment.

Clarification Statement: Emphasis is on using evidence to explain the influence each of the four factors has on number of organisms, behaviors, morphology, or physiology in terms of ability to compete for limited resources and subsequent survival of individuals and adaptation of species. Examples of evidence could include mathematical models such as simple distribution graphs and proportional reasoning.

Assessment Boundary: Assessment does not include other mechanisms of evolution, such as genetic drift, gene flow through migration, and co-evolution.

This resource is explicitly designed to build towards this performance expectation.

Comments about Including the Performance Expectation
HS.LS4-2 This unit consists of a sequence of carefully designed classroom activities, with students making a number of observations and inferences to develop a working model of natural selection. Because the activities build on each other, it is important that this unit is implemented as intended, with all activities being completed in the intended sequence and with the intended goals, rather than the ways in which they may have been used in the past. For example, after completing the fish simulation, the teacher should engage students in observations of the world around them, leading to students’ observations that populations of organism tend to stay relatively stable in size. This sets the stage for the next activity of students reflecting on why populations do not actually grow exponentially. The article contains a table with a column titled “Sample discussion focused on sense-making”. This column provides valuable examples of teacher and student dialogue, pushing students’ thinking. For example, during the Wormeater Game the teacher can prompt with “So we’ve observed there are a lot of variations, and there’s a struggle. Do you think these variations matter?” Throughout the unit students should be given enough time to reflect on their thinking and discuss it with each other. The authors’ intent as stated in their conclusion is to demonstrate "that a core model can anchor science instruction that includes all the practices called for in the NGSS." (p. 49). While there are references for some of the activities in the article, the particulars of some other activities are somewhat lacking. The “Oh Deer” game is not referenced. Instructions for this game can be accessed from Project Wild at and

Science and Engineering Practices

This resource is explicitly designed to build towards this science and engineering practice.

Comments about Including the Science and Engineering Practice
This unit is centered on the practice of Developing and Using Models. In the course of the unit, all of the eight science and engineering practices play a role, with the practice of Developing and Using Models serving as the anchor. The unit develops the driving question “How do populations change over time?” on the first day. This question is then used throughout the unit to focus students’ learning, as they engage in developing the model of natural selection. The strength of this unit lies in the fact that students develop their understanding of natural selection by actively engaging in the practices, rather than passively listening to the teacher explaining natural selection to them. For the first part of the unit students reason about natural selection, based on their observation and analyses of phenomena. Examples include the fish simulation, with students observing that populations have the potential for exponential growth, the “Oh Deer” Game, where students can infer that there is a struggle to survive within populations of organism, and the sunflower seed activity, where students observe that there is variation among organisms in a population. For the second part, students reason with the natural selection model to write Darwinian explanations (students to use the reasoning they have learned through actively participating in the activities to explain natural selection). Teachers can support students in sense-making and communicating by monitoring small group work and large group discussion with probing questions. See the section of the article titled “Tips for using models” (page 48). Making thinking public through students sharing their explanations via charts and keeping a record of student thinking as it develops throughout the unit, is an important aspect of this unit. It shows how the students’ model of natural selection develops as they engage in various activities, and supports students in making connections to other science concepts.

Disciplinary Core Ideas

This resource is explicitly designed to build towards this disciplinary core idea.

Comments about Including the Disciplinary Core Idea
This unit engages students in exploring the four factors that lead to evolution (1) the potential for a species to increase in number, for example the fish simulation (2) the genetic variation of individuals in a species due to mutation and sexual reproduction, for example the sunflower activity (3) competition for an environment’s limited supply of the resources that individuals need in order to survive and reproduce, for example the “Oh Deer” activity, and (4) the ensuing proliferation of those organisms that are better able to survive and reproduce in that environment, for example the worm-eater activity. Wall posters are used throughout this unit. They provide a mechanism of recording, refining, and highlighting the content knowledge that students develop through the activities. As the authors of this unit point out, it is important to make explicit that there is a difference between reasoning about the model of natural selection and reasoning with the model of natural selection. Students should understand that they reason about the model when they investigate phenomena, make observations and inferences, as they do when they are exploring the four factors that lead to evolution (see examples above) and that they reason with the model of natural selection, when they apply their knowledge to write Darwinian explanations, such as explaining the changes that occurred in the peppered moth populations and the Galapagos island tortoise populations. The article describes the summative assessment, asking students to use their natural selection model to propose an explanation of how the carapace changed over time in the different populations, no other details about this summative assessment are provided.

Crosscutting Concepts

This resource appears to be designed to build towards this crosscutting concept, though the resource developer has not explicitly stated so.

Comments about Including the Crosscutting Concept
Students, individually and as a group, develop a model of natural selection, which explains the changes observed in populations over time, from the various activities in which they engage in during this unit. While the crosscutting concept of cause and effect is not explicitly mentioned in the unit, teachers can emphasize it when students share their individual explanations, which are publicly displayed on class posters. The facilitation notes of the unit suggest that teachers take two class periods for the evaluation and revision of the explanations, and one more class period to address inaccurate Lamarckian language in the student explanations. By asking probing questions, and explicitly asking students to describe the cause and effect relationship between the different components underlying the model of natural selection, teachers can address this crosscutting concept. Teachers can also help students make connections to other topics they have studies, e.g. the fossil record, using the crosscutting concept of cause and effect.

Resource Quality

  • Alignment to the Dimensions of the NGSS: Throughout the unit, elements of the disciplinary core idea are significantly addressed as well as interwoven with the practice of modeling. As students reason about and with the model of natural selection, they are engaged in the practice of using a model, which anchors students’ engagement in a number of other practices. While the crosscutting concept of cause and effect is not addressed explicitly, it strongly underlies this unit. The lessons in the unit link together coherently to support students in making sense of the concept of natural selection and consequently applying their learning in writing Darwinian explanations.

  • Instructional Supports: This unit engages students in authentic and meaningful scenarios through the various activities, asking them to make sense of a variety of phenomena. Throughout the unit students are engaged in the practice of modeling, as well as several other practices. This unit engages students in three-dimensional learning, providing them with the opportunity to express their thinking when individually writing Darwinian explanations, which they share and revise, providing opportunities for students to express, clarify, justify, interpret and represent their ideas and respond to peer and teacher feedback. While there are no particular suggestions to differentiate instruction for student who are English Language Learners or students with special needs, the set-up of the unit allows the teacher to provide targeted support and feedback through direct interaction with these students, and/or partnering them with peers.

  • Monitoring Student Progress: Aside from helpful sample discussions, which note what the teacher and what the students might be saying for each of the activities, no other explicit support for monitoring student progress is provided. However, the student-created posters are good examples of formative assessments of three dimensional learning, although individual assessments are limited. Teachers can expand on the suggestions provided in the article and use supportive questioning throughout the unit. For example, teachers could use pre-assessment at the beginning of the unit that surfaces students’ existing ideas about natural selection. Teachers can design their own assessment probe, or use one of the existing assessment probes on natural selection published by Page Keeley ( Teachers should monitor and provide feedback to students as they construct their Darwinian explanations and draft their final summative assessment. Teachers can also model and guide students in providing constructive peer feedback

  • Quality of Technological Interactivity: Except for the exponential growth of fish activity, there is no interactive technology involved in this lesson. The simulation might provide some problems in loading, as it requires the user to accept Java plug-ins.