Teaching the Concept of MECHANISM OF EVOLUTION. By Cynthia Cheung and Preeti Sharma. Introduction to mechanism of evolution. You may know what evolution is (that is, the process of change over time), but you may wonder about how or why evolution occurs.
Teaching the Concept ofMECHANISM OF EVOLUTION By Cynthia Cheung and Preeti Sharma
Introduction to mechanism of evolution • You may know what evolution is (that is, the process of change over time), but you may wonder about how or why evolution occurs. • In this presentation, two main questions will be addressed: • How does evolution occur? • Why do organisms evolve? • By examining the mechanisms of evolution, these questions will be answered.
Lesson Sequence • Genetic variation • Natural selection • Sexual selection • Genetic drift • Applications and societal implications Curriculum expectations addressed: (Gr. 11 SBI3U) C1.1 Evaluate the possible impact of an environmental change on natural selection and on vulnerability of species. C2.1 Use appropriate terminology related to evolution, including but not limited to extinction, natural selection, phylogeny, speciation, niche, mutation, mimicry, adaptation and survival to the fittestC3.1 Explain the fundamental theory of evolution, using the evolutionary mechanism of natural selection to illustrate the process of biological change over timeC3.4 describe some evolutionary mechanisms, and explain how they affect the evolutionary development and extinction of various species
Diagnostic assessment Assessment for learning: • Do students understand evolution? • What misconceptions do students have? • What do they know already about the mechanisms of evolution? Sample anticipation guide statements: • Evolution is about progression of organisms from simple to complex. • Evolution can occur in individuals. • Natural selection chooses only the best organisms to survive. • There is more than one way to explain evolution. Students rate these statements ranging from strongly disagree to strongly agree (scale of 1 to 5). Discussion may follow, or teachers may collect assessments to inform future instruction.
Important to remember… • Genetic variation is the basis of mechanisms of evolution • Without genetic variation, mechanisms would not occur • There are three primary sources of genetic variation • Mutations • Gene flow • Sex
Lesson 1 – Genetic Variation - Mutations Mutations are random Not all mutations matter to evolution Mutations • Can be beneficial, neutral or harmful to organism • Mutations can occur in any cell of an organism • Somatic mutations occur in non-reproductive cells and won’t be passed on to offspring • Only mutations in reproductive cells will impact offspring and populations For example, the different colouration of this apple is caused by a mutation in a somatic cell. Therefore, the seeds of this apple will not carry the mutation. Gene flow Sex Definition: Mutations are changes in an organism’s DNA. These changes affect all aspects of the organism’s life.
Lesson 1 – Genetic Variation – Gene flow Mutations Two Sub-populations of Beetles Gene Flow Sex • Movement of genes from one population to another through migration • Leads to the transfer of genes • Changes the frequency of genes in original and new populations
Lesson 1 – Genetic Variation – Gene flow • Teaching idea: Gene flow role play • Students are randomly divided in two groups with different colour caps (or pinnies, or buttons) and are separated into two groups in the classroom. • Each coloured group denotes a population. • Students are instructed to either stay in their current population or move to the other population. • Give them three opportunities to move or stay • After activity, discuss: • How did the populations change? • What factors made you want to stay or move? • What factors may play a part in determining gene flow in nature? (e.g., physical barriers, resources like food, shelter, mating opportunity) Mutations Gene Flow Sex
Lesson 1 – Genetic Variation – Sex • Genetic shuffling results when two organisms undergo sexual reproduction • New combinations of genes are introduced • Introduces genetic variation Mutations Gene flow Sex • Exit Slip • 3 key things I learned today: • 2 things I found interesting: • 1 question I still have: Assessment for, of learning at end of lesson - students complete an exit slip and hand in as they leave:
Lesson 2 – Natural selection • Video to introduce concept: • Hummingbirds in Ecuador • Before video: • Ecuador is home to over 132 species of hummingbirds • Pose questions to focus learning: • How did such diversity in hummingbirds arise? • What mechanisms do the scientists in the video explain this diversity? • What are the four processes involved? • What features of hummingbirds are affected because of their environment? • During video (click image to the right to open video): • Students answer questions and take notes • After video • briefly discuss answers as a whole class
Lesson 2 – Natural selection • Teaching idea: Clipbirds • A hands-on activity to simulate evolution of beak sizes in birds • Beak sizes are simulated using clips of different sizes • Students carry out simulation where food availability varies from season to season • Students analyze results of activity and make connections to how natural selection affects bird beak size in natural populations Full lesson plan can be found at http://www.ucmp.berkeley.edu/education/lessons/clipbirds/
Lesson 2 – Natural selection • Assessment for, of learning: Individual case study • Students choose a short film to watch from http://hhmi.com/biointeractive/shortfilms/ • Each film focuses on a different example of natural selection • Students will hand in a written summary that addresses: • How natural selection affected their particular species • What adaptations have resulted • How the environment affected the evolution of the species
Lesson 3 – Sexual selection • Activating prior knowledge: What do you think “survival of the fittest” means? • Students write responses down on a slip of paper and hand in to teacher • Teacher reads responses out loud, without judgement • Students will revisit their response after viewing following comic strip • Misconceptions identified here and from the diagnostic assessment can be addressed during this activity
Discussion questions • When it comes to crickets, what does fitness mean? • Is calling good or bad for a cricket's fitness? • Give some examples of selection at work in this cricket story. • How does selection favour calling? • How does selection favour not calling? • Student self reflection – how has your understanding of “fitness” changed?
Lesson 3 – Sexual selection • Question: If a cricket’s call attracts predators, why do they still do it? Wouldn’t natural selection select for individuals that don’t call? • Introduce concept of sexual selection as another mechanism of evolution • Explains why some species of animals exhibit adaptations that jeopardize survival Why do male peacocks continue to display large and colourful plumage even though it may be harmful to its survival?
Lesson 3 – Sexual selection • Online simulation – Exploring sexual selection in guppies (individual student activity) • Why are guppies so colourful? Click on image to go to website
Lesson 3 – Sexual selection • Not all sexually selected traits are harmful to organisms • Guest Lecturer video: • In fruit flies, wings show great diversity in patterns • Sexual selection acts to select for individuals with spotted wings • Click image to watch video – excerpt is from part 10-14
Lesson 4 – Genetic drift • A change in a small and isolated population that takes place strictly by chance is referred to as genetic drift. • It is random and accidental. • The resulting change may provide no survival advantage for the organism.
Lesson 4 – Genetic drift • Assessment: Compare and contrast genetic drift with natural selection using a Venn diagram Need an extension for enriched students? Have them complete a Venn diagram that compares natural selection, genetic drift and sexual selection! Natural selection Genetic drift
Lesson 5 – Application and societal implications • Artificial selection: • By farmers for desired traits in plants and crops (e.g., organic farming) • Animal breeding (e.g., dogs, horses)
Lesson 5 – Application and societal implications • Artificial selection cont’d: • Genetic engineering (e.g., antibiotic resistance genes, DNA manipulation) • Used to evolve proteins with particular properties, such as modified enzymes or new antibodies.
Lesson 5 – Application and societal implications • Medicine • Research into evolution of antibiotic-resistant bacteria • Understanding genes responsible for disorders • For example: the Mexican tetra fish
Assessments • diagnostic assessment - anticipation guide • exit slips to assess learning during teacher-led instruction (K/U) • graphic organizers to summarize learning (K/U, T/I) • lab reports (e.g., Clipbirds, guppy simulation) (K/U, T/I, C) • Case study (e.g., natural selection) (K/U, A) • Discussions (K/U, C) As a summative task, students are asked to answer the question: how do evolutionary mechanisms affect my life? They will research a topic (an application or societal implication) and present their answer using one of the following methods : • Poster (traditional form, or electronic using Glogster) • written lab report • role-play/drama/ video • Powerpoint or Prezi presentation • lyrics and song • Evaluation of summative task will address the following achievement chart categories (T/I, C, A)
Differentiated instruction • Kinesthetic learners • will benefit from the hands-on activities and virtual labs • Auditory learners • will benefit from videos and mini-lectures • Visual learners • will benefit from videos • Activities vary • from whole class (e.g., discussions) to small groups (e.g., Clipbirds lab), to individual (e.g., online simulation) • groupings can be altered to suit class needs • Assessments vary • Student choice allowed where possible • Summative task allows choice based on interest and mode of presentation
Accommodations • Students with IEP’s: • accommodate according to IEP strategies and methods • provide additional time, extra support where needed • Students that are ELL’s: • provide graphic organizers to take notes • pair up with another student that speaks first language • pre-teach vocabulary by providing a glossary of key terms ahead of lesson • allow use of electronic dictionaries or online translation tools • use visual representations where possible to explain concepts • Enriched students: • allow independent study projects in a topic that interests them • independently find other examples of mechanisms at work and share with class/teacher • provide extensions to class activities
Possible student difficulties and solutions • Misconceptions about natural selection, especially about phrase “survival of the fittest” • See lesson 3 for details to address possible misconceptions • Students may find it difficult to understand the difference between somatic or genetic variation and why the latter is responsible for evolution. • Emphasize this point when teaching about mutations • Some students may object to the topic of evolution because it is incompatible with their religious faith. • send home a letter before unit; open up communication with parents • emphasize that evolution is a scientific theory that serves to explain observations we see in the natural world • may need to consult with head of department or admin if student refuses to participate in learning
Sample graphic organizer For summarizing key ideas • could be provided at the beginning of the unit to provide a big picture of the unit. • as learning occurs, students can fill in the blank spaces with key ideas of that subtopic. • could also be used at the end of a unit to summarize and review key ideas of the unit. • This can be differentiated for students in the following ways: • enriched students create organizer on their own; • include more pictures for ELL’s; • provide a completed copy for students with learning needs
References and sources • Farabee, M.J. (2001). Development of Evolutionary Theory. Retrieved July 17, 2012, from http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookEVOLI.htmlAn online source for concepts in evolution. • Howard Hughes Medical Institute. (2012). Biointeractive - Evolution. Retrieved July 17, 2012, from http://www.hhmi.org/biointeractive/evolution/index.htmlA collection of videos (lecturers, animations) and articles about evolution. • University of California Museum of Paleontology. (2012). How does evolution impact my life? Retrieved July 17, 2012, from http://evolution.berkeley.edu/evolibrary/search/topicbrowse2.php?topic_id=47A list of resources and topics for applications and societal implications. • University of California Museum of Paleontology. (2012). Understanding Evolution. Retrieved July 17, 2012, from http://evolution.berkeley.edu/evolibrary/teach/index.phpA comprehensive website that provides a deep conceptual understanding of evolution, as well as teaching strategies, common misconceptions, and tons of resources (e.g., image library, teaching materials database). • WGBH Educational Foundation and Clear Blue Sky Productions, Inc. (2011). Evolution library. Retrieved July 17, 2012, from http://www.pbs.org/wgbh/evolution/library/index.htmlA set of resources including books, articles, links and images related to topics in evolution.