To understand the concept of natural selection.
Through the use of an interactive activity, this lesson focuses on the concept of natural selection.
By the end of elementary school, students should know that individual organisms of the same kind differ in their characteristics, and that sometimes these differences give individuals an advantage in surviving and reproducing. Further, students should be able to look for ways in which organisms in one habitat differ from those in another and to consider how some of those differences are helpful to their survival.
This prerequisite knowledge should help middle-school students take this concept a step further by understanding that individual organisms of different kinds are more likely than others to survive and have offspring because of their particular traits. In addition, by the end of middle school, students should know that small differences between parents and offspring accumulate (through selective breeding) in successive generations, resulting in descendants that are very different from their ancestors.
Research has shown that students from middle school all the way up to college have difficulty with the concept of natural selection and adaptation. In terms of natural selection, students seem to have an inability to integrate two distinct processes in evolution, the occurrence of new traits in a population AND their effect on long-term survival. Many students understand that environmental conditions are responsible for changes in traits, or that organisms develop new traits because they need them to survive, or that they over-use or under-use certain bodily organs or abilities. However, many students have little understanding that chance alone also produces new heritable characteristics by forming new combinations of existing genes or by mutations of genes. Further, if they understand the concept of gene mutations, they generally see how it can modify an individual's life but not necessarily how this affects an individual's germ cells and thus one's offspring. Students also have difficulties understanding that changing a population results from the survival of a few individuals that preferentially reproduce, not from the gradual change of all individuals in the population. (Benchmarks for Science Literacy, p. 343.)
In terms of adaptation in the theory of natural selection, students of all ages often believe that adaptations result from some overall purpose or design, or they describe adaptation as a conscious process to fulfill some need or want. Elementary- and middle-school students tend to confuse non-inherited adaptations acquired during an individual's lifetime with adaptive features that are inherited in a population. (Benchmarks for Science Literacy, p. 344.)
Have students write down what they think "survival of the fittest" means. Give them five minutes to do this and then have a class discussion regarding what they each wrote down. Note: students will do this again at the end of the lesson in the Assessment section.
During the discussion, you will want to watch for student misconceptions and make sure they understand the following:
- In terms of natural selection, there are two distinct processes in evolution that are important to understand. First, the occurrence of new traits in a population occurs because of environmental conditions, survival needs, over-use or under-use of certain bodily organs or abilities, genetic mutations, and/or the formation of new combinations of existing genes. Point out that a genetic mutation OR the formation of new combinations of existing genes can affect the individual's life and that this change in genetics can be passed to one's offspring, thus affecting successive generations. Second, that these new traits have an effect on long-term survival.
- In terms of the big picture of natural selection, it is important that students understand that a change in a population results from the survival of a few individuals that preferentially reproduce and NOT from the gradual change of all individuals in a population.
- In terms of adaptation in the theory of natural selection, it is important to point out that populations change or adapt over generations inadvertently not deliberately! Thus, this type of adaptation is not a conscious process. It may be helpful to point out that there are different types of adaptation. For example, there are non-inherited adaptations acquired during an individual's lifetime AND there are adaptive features that are inherited in a population (e.g., natural selection).
To help introduce the concept of natural selection, students should use their Nowhere to Hide student esheet to watch Natural Selection on the BrainPOP website. You may want to use a computer and an overhead projector to show this movie to your students. Then, have students answer these questions in their notebook to solidify what they learned in the movie. (These questions were extracted from the BrainPOP quiz).
- How does natural selection work?
(Those who best adapt to their environment are the ones who survive and reproduce.)
- What did Darwin study to learn about natural selection?
(He studied finches.)
- What is a species?
(A set of organisms who share similar traits and can interbreed.)
- How does a new species come into being?
It branches off from an existing species, changing over time.)
- What happens after long periods of natural selection?
Also, there is a Nowhere to Hide student sheet (and corresponding teacher sheet) that has a matching activity for any students who may need extra review. Students can use their individual computers to find answers for this activity at the Evolution: Glossary on PBS's Evolution website if needed. Finally, there is a quiz associated with the website that does not need to be done. Relevant information has been extracted from this quiz and put in the matching activity (see student sheet).
Next, have students use the Nowhere to Hide student esheet to access the Nowhere to Hide interactive. This interactive is based on the story of the peppered moths that lived in the forests of Manchester England in the 1800s and were affected by a rise in pollution (read the Learn More section). In this activity, students will be able to observe the process of natural selection by changing the amount of pollution in an environment (i.e., the background color of the screen) and then observing its effects on the survival of the green and orange bugs.
The student esheet includes both instructions on how to play the interactive activity and questions regarding the activity (the Nowhere to Hide teacher sheet has the answers to these questions). Students can find the answers to the questions in the activity and the Learn More section.
The main point of this lesson is to help students understand the concept of natural selection including the meaning of "survival of the fittest."
Ask students to get together in groups (no more than four) and to come up with an explanation of natural selection and what "survival of the fittest" means. Give them five to ten minutes to do this activity. Then ask them to share what they wrote down.
Then share with them the explanation of the term natural selection obtained from the Frequently Asked Questions About Evolution page on the PBS Evolution site:
Natural selection is a process where individuals in a population who are well
adapted to a particular set of environmental conditions have an advantage over
those who are not so well adapted. The advantage comes in the form of survival
and reproductive success. For example, those individuals who are better able to
find and use a food resource will, on average, live longer and produce more
offspring than those who are less successful at finding food. Inherited traits that
increase individuals' fitness are then passed to their offspring, thus giving the
offspring the same advantages. This is also known as "survival of the fittest"!
Then have students come up with another activity that would demonstrate the process of natural selection. (Reminder: This one used pollution [background color] and different colored bugs.) What other scenario could they create and how would it work (e.g., birds have different beaks depending upon what type of food they eat; cactus finches have long beaks, the ground finch has a short beak, and the tree finch has a parrot-shaped beak). Information about these birds can be found on the Natural Selection in Real Time website.
Reminder: There is a student sheet (and corresponding teacher sheet) that has a matching activity for any students who may need a little extra review. Students can use their individual computers to find answers for the matching activity at the Evolution: Glossary of the PBS Evolution website if needed.
For another lesson on evolution, see The Rise and Fall of the Mammoths.
These websites discuss how various birds have adapted to a particular environment: