Lesson 2: Natural Selection
Background Information
With over a million living species on earth, students cannot ignore the vast diversity of living things. In elementary and middle school, they can enjoy their curiosity about nature and explore the many different organisms in many different capacities. It is in high school that an explanation for the diversity in living things itself must come to light.
Understanding evolution is the key to understanding diversity. And natural selection, being the mechanism (or cause) of evolution must also be understood. Though students may understand evolutionary change and how it works in a general sense, they need to broaden their thinking from the specifics of individuals with certain traits to how the traits in a whole population can change.
This lesson is an introduction to natural selection.
The Motivation introduces a species of bird that became (over millions of years) numerous species, through adaptation. The Development is a hands-on activity that demonstrates how populations change little by little, generation by generation, due to survival of species that have traits that are beneficial in an environment. Students will learn why organisms evolve over time, how natural selection works, and how certain factors determine survival and differences in organisms. This hands-on activity is probably more effective than any reading students will do on the subject, particularly if the subject is new.
Also, the lesson deals with natural selection itself. It does not bring up the discovery of natural selection or its discoverer, Charles Darwin. You may want to plan this lesson, however, in coincidence with such information.
Understanding evolution is the key to understanding diversity. And natural selection, being the mechanism (or cause) of evolution must also be understood. Though students may understand evolutionary change and how it works in a general sense, they need to broaden their thinking from the specifics of individuals with certain traits to how the traits in a whole population can change.
This lesson is an introduction to natural selection.
The Motivation introduces a species of bird that became (over millions of years) numerous species, through adaptation. The Development is a hands-on activity that demonstrates how populations change little by little, generation by generation, due to survival of species that have traits that are beneficial in an environment. Students will learn why organisms evolve over time, how natural selection works, and how certain factors determine survival and differences in organisms. This hands-on activity is probably more effective than any reading students will do on the subject, particularly if the subject is new.
Also, the lesson deals with natural selection itself. It does not bring up the discovery of natural selection or its discoverer, Charles Darwin. You may want to plan this lesson, however, in coincidence with such information.
Further...
Darwin C. (1859) The Origin of Species
''........can we doubt (remembering that many more individuals are born than can possible survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and procreating their kind? On the other hand, we may feel sure that any variation in the least injurious would be rigidly destroyed. This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection'
or in a most concise definition from contemporary Biologist Richard Dawkins: "the non-random survival of random variants."
Natural selection is a process (not a thing) which requires:
''........can we doubt (remembering that many more individuals are born than can possible survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and procreating their kind? On the other hand, we may feel sure that any variation in the least injurious would be rigidly destroyed. This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection'
or in a most concise definition from contemporary Biologist Richard Dawkins: "the non-random survival of random variants."
Natural selection is a process (not a thing) which requires:
- production of variation. (the random part)
- the actual selection (non-random)
Hook: Kinesthetic Activity
The link below leads to an activity that can be used to demonstrate natural selection:
The link below leads to an activity that can be used to demonstrate natural selection:
Action: Online Simulation
Natural Selection Interactive: http://phet.colorado.edu/en/simulation/natural-selection
Natural Selection Interactive: http://phet.colorado.edu/en/simulation/natural-selection
- Java must be installed on all computers before running the simulation
- Allow students to work in pairs to carry out the simulation, record, and answer the questions.
- Allow students to play around with the simulation for a few minutes at first with little instruction of how it works.
- After a few minutes, distribute the handout [file below] and instruct them to carry out experiments A-F and to fill out the chart under “Results” as they complete each experiment. Explain that a stable population is one that changes very little after a certain point.
- Have students complete the exploration and conclusion questions (1-9) by the end of the period
- Assign the “TAG” Challenge at the bottom of the page for homework Narrative/Practice
- Content: Selection Pressures (environment, predator/prey, resources, mate selection), fitness, heredity, Darwin’s Finches
- Allows you toggle biotic and abiotic selection pressures, add mutations, and choose which traits are dominant/recessive. Also allows you to view the progress of the population in 3 ways: through watching as the cartoon simulation changes, graphically, and by clicking on any individual animal to see their pedigrees.
- Very good for visual learners.
natural_selection_simulation.doc | |
File Size: | 59 kb |
File Type: | doc |
Lecture on Natural Selection:
Consolidation
_http://www.youtube.com/watch?v=aTftyFboC_M
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Additional Teaching Resources
Another Natural Selection Simulation
http://sciencenetlinks.com/media/filer/2011/10/07/evolution.swf
- Simple simulation demonstrating similar phenomena to the Peppered Moth case.
- Shows how predators feed off insects of both camouflaged and non camouflaged phenotypes, yet the camouflaged species tend to have the highest survival; demonstrates selective pressure
- Shows how an insect of one colour can reproduce to form progeny of both colours thus demonstrating mutation and genetic variation.
- Demonstrates how the colour of the species that survive changes as the colour of the environment changes and thus adaptability of the population thanks to variation.
- Can be used effectively to debunk misconceptions and stimulate discussion on the topic.
Article about the adaptation of Finches
http://www.unisci.com/archives/20003/0725001.htm
The article, without much detail, tells the story of one species of finch that came to the island of Kaua'i several million years ago. It describes how the one population adapted over millions of years to the food and habitat.
The following discussion questions will help you determine what your students know about adaptation. It is a commonly misunderstood concept (see above). If students cannot answer the questions, that is fine. This situation could even prove to be better because it means you are starting with a clean slate. If they answer them incorrectly, the development should address any misunderstandings.
Ask the following:
The article, without much detail, tells the story of one species of finch that came to the island of Kaua'i several million years ago. It describes how the one population adapted over millions of years to the food and habitat.
The following discussion questions will help you determine what your students know about adaptation. It is a commonly misunderstood concept (see above). If students cannot answer the questions, that is fine. This situation could even prove to be better because it means you are starting with a clean slate. If they answer them incorrectly, the development should address any misunderstandings.
Ask the following:
- What were some characteristics the finches developed to give them an advantage in surviving?
- How do you think the one species of finch evolved into many different species, each with its own advantages?
- Do you think these advantages helped them survive and reproduce?
- What might have happened if they didn't evolve into many different species?
- What were the environmental changes that led to the demise of many species of finch?
- Do you think that environmental changes are always bad for a species or do you think such changes can actually help certain species?
- Do you think that extinction can occur because of environmental changes? Why? Why not?
- What do you think will happen to future generations of finches? Why?
Further Discussion about Natural Selection
http://www.unisci.com/stories/20011/0214016.htm
Above is a recommended article from the UniSci site that focuses on another aspect of adaptation. The article not only covers how animals have adapted to a habitat, but how the successful survival of the animals can in turn impact the habitat
Above is a recommended article from the UniSci site that focuses on another aspect of adaptation. The article not only covers how animals have adapted to a habitat, but how the successful survival of the animals can in turn impact the habitat