What Darwin Never Saw
Lesson Introduction
As seen in the video, What Darwin Never Saw, the Galapagos Islands are filled with remarkable creatures. Some of the species (definition) have been linked to others from South America, but they have changed in ways that make them more suitable to their current environment.
For example, giant tortoises are found in two varieties: domed or saddlebacked. Their "creation" depended on the food that was available to them. If the tortoises had to raise their heads to eat from trees or bushes, they became saddlebacked. If they had to eat off the ground, they became domed. They evolved as slow movers because there were no other predators and there was no need to be fast. Throughout history, people have been their biggest threat. Pirates in the 1830's used to load their ships up with tortoises. Now, these tortoises, which give the Galapagos islands their name, are more and more endangered (definition) every year.
In the Galapagos, there are also species of birds which have given up their wings, and their ability to fly, in favor of shore living. There are iguanas that live on land, like those in South America, but they are darker in color because they have been successful in using the lava as a safe background. In this lesson, students work together in groups to make ongoing observations of salamanders. Over time, they see the animals change to adapt to different environments. They keep journals of their observations and they make their own conclusions based on what they see.
Grade Level
6 through 12
Objectives
The students will:
1. conduct an experiment with two different conditions.
2. keep data from their observations and make their own conclusions based on the data.
Time Allotment
one 40-minute session for set-up, with regular observation and data collection sessions
Materials
two salamanders
two tanks
student journals
pencils or pens
video/video player
Books to Read
Amphibians of Montana, by J.H. Black, Helena, MN: Montana Fish and Game Department, 1970.
Human Evolution, by Bernard Campbell, New York, NY: Aldine, 1985.
Reptiles and Amphibians of Minnesota, by W.J. Breckenridge, Minneapolis, MN: University of Minnesota Press, 1944.
Advanced Preparation and Teacher Notes
Salamanders are easy to keep in a classroom, but as with all live specimens, care must be taken to provide a quality habitat for the animal. Temperature and humidity is very important for salamanders. They can be fed worms, water insects, crayfish, mollusks, frogs, fish eggs and small minnows.
Procedure
Tap Prior Knowledge
1. Ask the students to think about adaptations they have witnessed in plants and animals. How do these adaptations make them better suited for their habitats? Show the section of the What Darwin Never Saw video (from 22 14 to 26 18) which shows the giant tortoises on Galapagos Islands. Discuss how they have adapted to their habitat.
Share with Neighbor/Revise Ideas
2. Have students write a short description of a successful adaptation and share it in their groups. Allow them to add to their descriptions following the sharing session. Share one of the biographies from our Career Connections with the students.
Engage Students in a Hands-on Activity
3. Set up an experiment to see the effect of environment on salamanders. Use the two tanks to represent two very different environments. Make one very aquatic and the other mostly terrestrial, with only a minimum of water to satisfy the needs of the animal. Have students make observations of the habitats and write them in their journals before going any further.
4. Begin with both salamanders in the same aquatic tank. Make observations for a week or two. Move one into the drier tank, while the other stays where it was. Introduce the idea of a control situation. Continue to make observations of both salamanders. Is one changing more than the other? Is one changing at a different rate?
Introduce the Scientific Principle/Concept
5. Most amphibians begin life in water and the later change to adapt to life on land. They replace their gills with nostrils and lungs so that they can breathe the air. They grow legs so that they can get around on land.
6. The salamanders in this investigation will not be "evolving" in the sense that plants, animals, and even humans have evolved in the past. One individual member of a species does not evolve. Still, it is a good chance for students to observe animal adaptations. It can lead to a deep discussion of natural selection and evolution. After many generations, only salamanders that can adapt because they have certain favorable traits would likely survive and have offspring. In this way, changes in environmental conditions can affect the survival of individual organisms and entire species. On a larger scale, small differences between parents and offspring can accumulate (through selective breeding) in successive generations so that descendants are very different from their ancestors.
7. Natural selection provides the following mechanism for evolution: Some variation in heritable characteristics exists within every species, some of these characteristics give individuals an advantage over others in surviving and reproducing, and the advantaged offspring, in turn, are more likely than others to survive and reproduce. The proportion of individuals that have advantageous characteristics will increase.
8. Explain to students that from time to time, major shifts occur in the scientific view of how the world works. Change and continuity are persistent features of science. Think about continental drift as another example of a current theory that we commonly accept now. Alfred Wegener first proposed it and hardly anyone believed it could be true. Now, we don't refer to it as a theory. It is accepted. No matter how well one theory fits observations, a new theory might fit them just as well or better, or might fit a wider range of observations. In science, the testing, revising, and occasional discarding of theories, new and old, never ends.
Lesson Assessment
9. Collect the students' journals and check for accuracy and completion. Each entry should be dated and the conclusions should be based on the observations.
Connect to Other Everyday Examples
10. Give students a chance to surf the World Wide Web for more about animal adaptations:
