Natural Selection

Contributor
PhET™ interactive Science Simulations
Type Category
Instructional Materials
Types
Simulation
Note
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.

Reviews

Description

This interactive simulation allows students to explore natural selection in bunnies by controlling factors in the environment (equator or arctic environment),  selection factors (wolves, food), and characteristics of the bunnies (fur color, tail length and teeth length). The bunnies in the default setting in the simulation have white fur, short tail, and short teeth. There is an option to introduce mutations, which causes bunnies with brown fur, long tail, or long teeth to appear. The user can also edit genes (select whether the mutation for fur color, tail length and teeth length is dominant or recessive). The simulation output includes a chart with the population of bunnies (number of bunnies) on the y-axis, plotted against time on the x-axis. There is an option to see a pedigree when the user clicks on an individual bunny moving within the environment (equator or arctic).

Students can make predictions and/or ask questions prior to running the simulation. They can run the simulation, controlling and changing variables, and analyze the data generated by the simulation (output graph).

The simulation itself does not come with instructions or a lesson plan. However, there are several lesson plans posted on the website. These lesson plans are from authors independent of the authors of the simulation. This review is limited to reviewing the PHET natural selection simulation, and not any of the lesson plans from outside authors.

A related resource, called Quackers and Cottontails, that uses this simulation is available at https://www.nms.org/Portals/0/Docs/FreeLessons/BIO_Quackers%20and%20Cottontails_web.pdf. This lesson plan is published by the National Math and Science Initiative (NMSI). The Cottontail portion of this lesson plan is using the PHET simulations. If teachers are using the Quacker portion of the lesson plan as well, it is important to discuss the limitation of the Quacker simulation, so students do not walk away with misconceptions. This review is limited to the PHeT natural selection simulation itself, not any of the related resources or lesson plans.

Intended Audience

Educator and learner
Educational Level
  • Grade 8
  • Grade 7
  • Grade 6
  • Middle School
Language
English
Access Restrictions

Free access - The right to view and/or download material without financial, registration, or excessive advertising barriers.

Performance Expectations

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.

Clarification Statement: Emphasis is on using simple probability statements and proportional reasoning to construct explanations.

Assessment Boundary: none

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

Comments about Including the Performance Expectation
This simulation gives students an opportunity to observe and describe how the increase in number of bunnies (“add a friend” in the simulation starts the bunnies reproducing), genetic variation of individual bunnies (click on mutation in the simulation and then observe the phenotype of the bunnies populating the environment), competition for food and predation by wolves leads to the proliferation of those bunnies that are better able to survive and reproduce in the environments. Teachers should embed this simulation into their instructional sequence where they feel it best fits since no direct instruction on natural selection occurs during the simulation. Teacher questioning and support of students is dependent on student background knowledge of the concept and their familiarity with simulations. Students should be working on this simulation with a partner, so they have the opportunity to discuss what they are observing, what questions they could be investigating with this simulation, how to display and analyze data, and how to write an evidence-based explanation answering their questions. Teachers should monitor for student understanding throughout the activity, and use some form of large-group share-out to make sure that all students are making progress toward the performance expectation. Constructing an explanation based on evidence is not included in the instructions, but could easily be added by the teacher. This could be done in the format of a Darwinian Explanation (see tips in the Disciplinary Core Idea for a detailed description). Other practices such as using models, planning and carrying out investigations and analyzing and interpreting data can easily be incorporated into what the students do. Depending on where in the unit teachers are using this simulation, the following directions and prompts can be helpful in supporting students to make progress toward meeting the Performance Expectation. These questions/prompts are adapted from the related resource “Quakers and Cottontails” (Cottontails portion only) https://www.nms.org/Portals/0/Docs/FreeLessons/BIO_Quackers%20and%20Cottontails_web.pdf. Introduction to the Simulation What variables are you able to manipulate in this simulation? Start the simulation by clicking the “PLAY” button. What happens if you never “add a friend?? Explain. Add a friend. Let the simulation continue to run until it stops, and then discuss what happens. Explain what “selection” factors were lacking for this to occur. What happens to the population sizes of the two phenotypes after several more generations? Explain why you think this occurred? Using the Simulation to Investigate Natural Selection The teacher can provide a question for the students to investigate, or students can develop their own question. An example question to investigate with the simulation found in the Cottontail lesson plan is: “A population of short-toothed and long-toothed bunnies is living in the Arctic. Due to harsh conditions food becomes limited. What happens to the population sizes of both phenotypes over the next 10 generations? “ Teacher should encourage students to plan their investigation (think about how to run the simulation, so that they can collect data that answers their question), create a data table to keep track of the number of individual bunnies with the two phenotypes in each generation, and graph their data for an additional visual representation. Based on this evidence, students should write and share an evidence-based explanation that answers their question. Teachers should make sure to include a discussion on the limitations of the simulation in comparison of what might happen in the real world when students share their evidence-based explanations.

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
The simulation output includes visual observations of what is happening to the bunnies in the environment, as well as an output graph. Students can organize and analyze the data. Teachers can support students in this process by having students make their data displays public and compare in a large group discussion.

This resource appears to be designed to build towards this science and engineering practice, though the resource developer has not explicitly stated so.

Comments about Including the Science and Engineering Practice
This simulation, with the opportunity to manipulate several settings, allows students to plan a number of different investigations, collecting data to answer their questions. Students can run the same experimental set-up a number of times to compare the results from the different trials. Students may initially require support to come up with a productive experimental design, which provides a good learning opportunity. Teachers should use probing questions and encourage students to try out different approaches, rather than telling students step-by-step what to do.

This resource appears to be designed to build towards this science and engineering practice, though the resource developer has not explicitly stated so.

Comments about Including the Science and Engineering Practice
While students have not developed the model underlying the simulation, they can use it to investigate factors (the potential for a species to 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 the environment) that influence the process of evolution. Students often struggle with distinguishing what happens to the individual as opposed to the population over time when studying natural selection. This simulation gives students the opportunity to see what happens to the phenotypes of bunnies over several generations when manipulating selection factors. Teachers should explicitly probe for students’ understanding of this aspect during instruction.

Disciplinary Core Ideas

This resource appears to be designed to build towards this disciplinary core idea, though the resource developer has not explicitly stated so.

Comments about Including the Disciplinary Core Idea
This simulation provides students with the opportunity to manipulate and explore the interaction of factors leading to evolution, and observe how natural selection leads to adaptation, i.e. a population of bunnies suited to survive and reproduce in the environment that students selected by manipulating the settings. Teachers should make sure that students do not just “play” with the simulation, or just “observe” what happens. Instead, after students describe what is happening to the populations of bunnies as they run different trials with different settings, teachers should ask what that means, and ask students to collaboratively develop and defend explanations based on evidence they collected when running the simulation. The explanation could take the form of a Darwinian Explanation where students describe the variations in the population at the beginning of the simulation, the selective advantage in the particular environment, which variations survived, reproduced and passed on their genes more and how the population changed from the beginning of the simulation to the end. Hilbish and Goodwin, 1994 recommend including real-life demonstrations using living organisms and selection pressures familiar to students in addition to simulations when teaching natural selection. From their research findings, they report that the exclusive use of simulations to teach natural selection tends to have students think of natural selection as something intangible rather than a process that actually occurs (Koba, S., Tweed, A. 2009. Hard-to-Teach Biology Concepts. A Framework to Deepen Student Understanding, NSTA press) Teachers could have students analyze data about Darwin’s finches in the Galapagos or Rock Pocket Mice in the southwesten part of the United States for real life examples where all the parts of natural selection have been studied and documented, including the genes responsible for a selective advantage.

This resource appears to be designed to build towards this disciplinary core idea, though the resource developer has not explicitly stated so.

Comments about Including the Disciplinary Core Idea
The tips associated with the Disciplinary Core Idea LS4.C Adaptation are relevant to the Disciplinary Core Idea LS4.B Natural Selection one also since the process of natural selection leads to adaptations. The teacher can make sure that student explanations are explicit about the link between these two disciplinary core ideas.

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
This simulation provides students with the opportunity to manipulate and explore the interaction of factors leading to evolution, and observe how natural selection leads to adaptation, an example of a cause and effect relationship. The teacher should use questioning strategies to help students understand cause and effect relationships within this simulation. For example students should articulate that when a mutation occurs that provides individual bunnies with the advantage to blend into the background, they are more likely to not be eaten by the wolves, survive and reproduce, which over many generations leads to a higher proportion of bunnies with a fur color that blends into the background.

Resource Quality

  • Alignment to the Dimensions of the NGSS: Elements of the disciplinary core idea are significantly addressed since traits such as white fur in an arctic environment that support successful survival and reproduction in a new environment became more common and those such as brown fur that are less successful become less common. The prevalence of the genes that controls these traits has changed from the beginning to the end of the scenario. Use of the simulation provides opportunities to address the practices of using a model, planning and carrying out investigations, and analyzing and interpreting data, as well as describing the cause and effect relationships that are part of the mechanisms of natural selection. The crosscutting concept of cause and effect should be made more explicit by the teacher during instruction. All of these connections require that the teacher purposefully facilitates students’ use of the simulation, so that students make meaning of what they are observing.

  • Instructional Supports: The simulation does not provide instructional supports. Incorporating many of the suggestions in the “Tips” above could help students develop deeper understanding of natural selection, the practices of Using Models, Planning and Carrying out Investigations and Analyzing and Interpreting Data and the crosscutting concept of cause and effect. No support for differentiated instruction for English Language Learners, those that have special needs or those who read below grade level are suggested. Since it is an online simulation there is limited reading and many struggling students may be able to understand the process of natural selection from interacting with the phenomenon. Having students fill out a flowchart of the major aspects of natural selection would be one way to make an explanation accessible to all students.

  • Monitoring Student Progress: The simulation does not provide a method for monitoring student progress. However, the teacher could easily implement the simulation in a way to monitor students’ progress. For example, pairs of students could prepare a presentation that includes the question they investigated, the evidence they collected when they ran the simulation, and their evidence-based explanation answering the question they asked. The teacher could also use the simulation with the whole group and ask questions to check for understanding. Students could also write a Darwinian Explanation as outlined in the section on the Disciplinary Core Idea.

  • Quality of Technological Interactivity: The simulation is straightforward to use and provides numerous ways for students to manipulate it. The functionality is directly related to learning about natural selection.