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Multiple mechanisms of evolution Name(s): Jesse Lasky Title of lesson: Multiple mechanisms of evolution Date of lesson: 4/9/09 Length of lesson: 70-100 minutes, depending on the students Description of the class: Name of course: Grade level: 7th grade Honors or regular: Regular Source of the lesson: The natural selection portion of the lesson is modeled after an activity mentioned to me by Timothy Keitt, the rest is my creation. 1. Overview This lesson is geared toward getting students to learn that there are multiple mechanisms of evolution, that natural selection is but one of them, and that determining which mechanism led to current patterns is often difficult to ascertain. II. Performance or learner outcomes Students will be able to describe three mechanisms of evolution. They will describe the forces driving each mechanism. They will describe possible outcomes of each mechanism. III. Resources, materials and supplies needed 1. Copious amounts of Skittles and M&Ms. Approximately 1 bag of Skittles for each group, and 1 large bag of M&Ms for each group (see below). 2. 2 bowls will be needed for each group. 3. A notebook to record data IV. Supplementary materials, handouts. (Also address any safety issues Concerning equipment used) N/A V. Safety Issues Students should wash their hands beforehand, because they will certainly end up eating some of these. Make sure to buy plain M&Ms in case students are allergic to peanuts. Make sure any students allergic to chocolate or who cannot eat sugar are not eating M&Ms. Five-E Organization Teacher Does Probing Questions Student Does Will probably come up with an Define “evolution” in your Engage: example of natural selection. review the definition of evolution, ask own words. Something affects the survival groups to each come up with a specific Describe a way in which an or reproduction of individuals scenario for some potential evolutionary organism might evolve. How with a certain trait, and those change. could a bag of M&Ms evolve most successful pass on their (change over time)? genes to future generations. Approx. Time__5__mins The other mechanisms discussed below, or sexual selection (e.g. peacocks), may also be described. Student should state that genes Students should be asked the Evaluation(Decision Point are the basis of heredity, and above questions. Different Assessment): they should describe some proposed mechanisms of mechanism capable of changing evolution that students come a population's gene frequencies. up with should be written on Heredity may also occur the board. Later we will through epigenetic address their accuracy. mechanisms, although genes are the predominate carriers of information determining phenotypes passed from one generation to another. Explore: Divide the students into groups, with at least two groups for each rule of evolutionary change. Ask each group to make predictions about how the composition of their population of M&Ms will change over time. Ask them to predict how consist this outcome would be across many populations (or student groups). Ask students to predict which rule of change will result in the greatest change in M&M composition. See the end for instructions for the simulations with different “rules” (i.e. mechanisms of evolution). If time is available, you may wish to have each group do a simulation of each rule of evolutionary change. During prediction making: will the M&Ms become homogenous (all of one color)? Which mechanism will result in the fastest change? During simulation:Are the M&M populations evolving? Why or why not? Is the amount of M&Ms of each color changing over time? Why? Why do the proportions not stay constant? How is this similar to actual organisms in nature? When I taught this, I did it in a 45 minute period, and there was not enough time to both go over the directions for all rules of evolution AND run the simulations. The students need reminded of the rules multiple times (at least with a group of students who were average at following directions). As a result the students only carried out the natural selection rule, and they largely were able to identify the mechanism for change and the likely outcome of such a force on the proportion of M&Ms of different colors. We were not able to get to the part of comparing the different rules. Approx. Time__10__mins Evaluation(Decision Point Assessment): Natural selection students (rule #1) should state that their preference for certain colors of M&Ms reduced the number of these M&Ms, and the other colors persisted.. Neutral genetic drift students (rule #2) should state that there are random fluctuations in the proportions of M&M colors because of the random deaths. Students in bottleneck groups (rule #3) should also state that the change is random, but they should recognize that there will likely be dramatic differences between the original and final population of M&Ms. Pass among groups asking the questions about the mechanism behind evolution in each group. Ask students to explain why their predictions fit or do not fit with the observed data (outcome). All students should be able to identify the mechanisms behind their evolutionary change, and they should describe the changes in the population in relation to those mechanisms. Explain: Students present their evolved (i.e. changed) populations to the rest of the class. Ask students whether the candy evolved over time and why (how does what they saw fit with the definition of evolution as change in a populations gene frequencies over time)? Give them a representative, unevolved, “normal,” straight out of the original M&M bag population to hold up in comparison to their final, post-evolution population. They describe the rule of evolution and why it created the observed final population. They should give an example to the class of the changes in frequency of a few of the colors from start to finish. They give a hypothetical example in nature. Approx. Time___5__mins Evaluation(Decision Point Assessment) As groups are presenting, ask each group to listen and think about the following questions: What is similar about the evolution of each group? (you can put these on the overhead projector, or have groups stand up at the front and hold them up) What is different? Does the outcome of some of the mechanisms (or “rules”) of evolution produce more consistent results than other mechanisms? Why? After presentations are done, have groups discuss these questions for ~2 minutes and have a few groups share with the class. Students state that the natural selection experiments should provide more consistent results because the mechanism is based on species traits, whereas it is random for the other groups. Depending on the results, students may observe that the bottleneck results have the most variability and the least predictability. Have student groups describe the cause and effect of each kind of evolution. If time permits have individual students repeat this orally or in a journal or quiz format. Students should describe the mechanisms underlying each group’s evolutionary change, and link that cause to the observed effect. Extend / Elaborate: Further discussion, either as a group or back in their original pairs or small groups. Students may make pie graphs showing original composition of the group and final composition, or they may make graphs with multiple lines showing the change in each M&M color frequency over time. Students may come up with their own animals and write a story saying how they could evolve in each of the 3 ways we saw. Approx. Time__5___mins Evaluation(Decision Point Assessment): Does the color of the M&M make a difference in the no Skittle populations? Does natural selection give M&Ms some trait they “need”? Did M&Ms “try” to adapt? What if only purple M&Ms were safe from predators, would M&Ms persist? (NO, there are NO purple M&Ms, unless they propose humans can create them). But this gets at whether students understand that selection cannot create different kinds of phenotypes, it can only act on already existing phenotypes. In natural populations, where does the variation in M&M come from? How is it transmitted to future generations? If I showed you a population of M&Ms that had no blues, what would you conclude about the evolution of these M&Ms? Discuss these questions and determine if students are adding misconceived mechanisms to evolution. Students often think that natural selection acts and gives species traits they “need,” and that individuals “try” to adapt. Natural selection only acts on existing variability in populations, resulting in differential fitness of phenotypes. Students should state that these alternative mechanisms of evolution can create similar patterns. If they do not realize this, advocate an opposing mechanism to the one they first proposed for the above question about “If you found a population of only red, yellow ...” Get them to defend their position, or they may give in and identify alternative explanations for observed patterns Additionally, present them with evidence from their simulations, where different rules may have resulted in similar outcomes. Evaluate: Students should be able to design studies that would allow them to compare the competing hypotheses that explain how traits arise. Have each group come up with an example organismal trait to study, and what kinds of data they could collect in order to rule out or to support each hypothesis. Approx. Time___5__mins For any given information they propose to collect, ask them which specific hypotheses it either supports or refutes. Ask them how many hypotheses information can support or refute (multiple). How can we show that one of these rules is or is not acting on a population? Students should design experiments or suggest data collection that would test the individual steps that must occur in each of these mechanisms of evolution. Some students may deny the existence of evolution. For the scope of this lesson, ask them if they saw evolution in the M&M populations and why or why not? (If the frequencies of M&M colors changed over time, this is evolution). Ask the students if they agree that something similar could happen in nature, and to come up with a hypothetical example. Many anti-evolutionists acknowledge micro-evolutionary change (small changes), but deny the common ancestry of all species (large changes between species). This nuance is beyond the scope of this lesson, although it is worth pointing out to students that scientists have found single genes (like the M&M colors) that can have dramatic impacts on development (e.g. determining whether something has 4 or 6 legs). STUDENT DIRECTIONS FOR ALL GROUPS: ANYONE NOT FOLLOWING DIRECTIONS IS ELIMINATED AND CANNOT EAT ANYTHING We are studying populations of M&Ms. Sometimes many M&Ms are killed by disasters all at once. Evolutionary Rule #1 1. You will receive M&Ms. Students put 2/3 of the M&Ms in an empty ziplock bag marked "Offspring," and the other 1/3 in a bowl or dish. 2. Students must go through 3 generations 3. Each student picks their favorite color of M&M. They may only eat that color. Generation A. At each generation the group records the number of M&Ms of each color. B. Then each group member takes turns selecting one M&M and eating it Students go around 2 times doing this so that each student selects twice each generation. C. Once all students have gone, record the number of surviving M&Ms of each color, and add one M&M child of the same color from the offspring bag for every pair of the parent M&Ms in the population. If only one M&M remains of a color, it has no offspring. 3. In the last generation, the students should write down how many M&M children would be added to the population, but you do not need to add them to the dish. Evolutionary rule #2 1. You will receive M&Ms. Students put 2/3 of the M&Ms in an empty ziplock bag marked "Offspring," and the other 1/3 in a bowl or dish. 2. Students must go through 3 generations Generation A. At each generation the group records the number of M&Ms of each color. B. Each student closes their eyes and selects one M&M and eats it. C. Once all students have gone, record the number of surviving M&Ms of each color, and add one M&M child of the same color from the offspring bag for every pair of the parent M&Ms in the population. If only one M&M remains of a color, it has no offspring. 3. In the last generation, the students should write down how many M&M children would be added to the population, but you do not need to add them to the dish. Evolutionary rule #3 1. You will receive M&Ms. Students put 2/3 of the M&Ms in an empty ziplock bag marked "Offspring," and the other 1/3 in a bowl or dish. 2. At the first generation, each student closes their eyes and picks 7 M&Ms and eats them. It is as if a hurricane, flood, fire, or other natural disaster came along and wiped out almost all of the M&Ms. 3. Once all students have gone, record the number of surviving M&Ms of each color, and add one M&M child of the same color from the offspring bag for every pair of the parent M&Ms in the population. If only one M&M remains of a color, it has no offspring. 4. In the second generation, the students record the number of each color of M&Ms in the population, and then add one M&Ms child of the same color for each parent M&Ms in the population. 5. Finally in the third generation, the students record the number of each color of M&Ms in the population, and then add one M&Ms child of the same color for each parent M&Ms in the population. Data sheet Generation Beginning of generation 1 Surviving at end of generation 1 Beginning of generation 2 Surviving at end of generation 2 Beginning of generation 3 Surviving at end of generation 3 # Red M&Ms #Yellow M&Ms #Green M&Ms #Blue M&Ms #Brown M&Ms #Orange M&Ms