with the use of genetic data to construct an evolutionary tree. They then analyze a subset of the data that evolutionary biologists have gathered in recent decades to determine the evolutionary relationships of Hawaiian drosophilid species. By working in small groups, students can acquire a common set of experiences that will help them share their ideas and conclusions. They also can acquire and model the information and skills they will need to analyze larger and more complex data sets.
In the explanation activity, students use the evolutionary tree they have constructed along with information about the history of the Hawaiian islands to develop hypotheses that could explain the current distribution of the four species being studied. By presenting their hypotheses in the form of narratives, they can demonstrate their understanding of important concepts in their own words and focus on understanding the ideas central to the investigation.
In the elaboration activity, students analyze additional data to decide whether their hypotheses need to be modified or whether to clarify and extend their explanations. The elaboration phase can be extended (bringing the total time spent on the exercise to three or four class periods) or minimized (in which case the exercise can be done in two class periods) depending on the time available. This activity also can lead to further investigations for interested students.
The evaluation activity is an ongoing diagnostic process that allows teachers to determine if learners have attained understanding. A rubric is provided to help assess student learning. Summative questions and assignments also are provided to evaluate the extent to which students understand the concepts developed in the investigation.
According to the National Science Education Standards (National Research Council, 1996), science education needs to provide students with three kinds of scientific skills and understanding. Students need to learn the principles and concepts of science. They need to understand and be able to apply the skills and procedures of inquiry that scientists use to investigate the natural world. And they need to understand the nature of science as a particular kind of human endeavor.
This teaching exercise fosters learning in all three of these areas. With regard to the principles and concepts of science, it embodies the following understandings drawn from the National Science Education Standards:
Species evolve over time. Evolution is the consequence of the interactions of (1) the potential for a species to increase its numbers, (2) the genetic variability of offspring due to mutation and recombination of genes, (3) a finite supply of the resources required for life, and (4) the ensuing selection by the environment of those offspring better able to survive and leave offspring.
The great diversity of organisms is the result of more than 3.5 billion years of evolution that has filled every available niche with life forms.
Natural selection and its evolutionary consequences provide a scientific explanation for the fossil record of ancient life forms, as well as for the striking molecular similarities observed among the diverse species of living organisms.
The millions of different species of plants, animals, and microorganisms that live on earth today are related by descent from common ancestors.