Types of Natural Selection

Graphs of the three types of natural selection
Chart By: Azcolvin429 derivative work: Azcolvin429 (Selection_Types_Chart.png)

One important thing for teachers to do after introducing a new concept is to check for complete student understanding of the main ideas. They also must be able to use the new knowledge and apply it to other situations if a deep and lasting connection of other scientific and evolution concepts is to be obtained. Critical thinking questions are a good way to monitor a student's understanding of a complex topic such as the different types of natural selection.

After a student has been introduced to the concept of natural selection and given information about stabilizing selection, disruptive selection, and directional selection, a good teacher will check for understanding. However, sometimes it is hard to come up with well constructed critical thinking questions that apply to the Theory of Evolution.

One type of somewhat informal assessment of students is a quick worksheet or questions that introduce a scenario to which they should be able to apply their knowledge to come up with a prediction or a solution to a problem. These types of analysis question can cover many levels of Bloom's Taxonomy, depending on how the questions are worded. Whether it is just a quick check on understanding vocabulary at a basic level, applying the knowledge to a real world example, or connecting it to prior knowledge, these types of questions can be adapted to the class population and the teacher's immediate needs. Below, there are some of these types of questions that use a student's understanding of the types of natural selection and links it back to other important ideas of evolution and various other science topics.

Analysis Questions

Use the scenario below to answer the following questions:

A population of 200 tiny black and brown birds is blown off course and ends up on a fairly large island where there is a lot of open grassland with small shrubs right next to rolling hills with deciduous trees. There are other species on the island such as mammals, many different types of vascular and non-vascular plants, an abundance of insects, a few lizards, and a somewhat small population of large birds of prey similar to hawks, but there are no other species of small birds on the island, so there will be very little competition for the new population. There are two types of plants with seeds edible for the birds. One is a small-seeded tree that is found on the hills and the other is a shrub that has very large seeds.

1. Discuss what you think might happen to this population of birds over many generations with respect to the three different types of selection. Formulate your argument, including backing evidence, for which of the three types of natural selection the birds will likely undergo and debate and defend your thoughts with a classmate.

2. How will the type of natural selection you have chosen for the population of birds affect the other species in the area? Choose one of the given other species and explain what sort of natural selection they may undergo because of this sudden immigration of small birds to the island.

3. Choose one example of each of the following types of relationships between species on the island and fully explain them and how co-evolution may occur if the scenario plays out how you described it. Will the type of natural selection for these species change in any way? Why or why not?

  • Predator and Prey relationship
  • Mutualistic relationship
  • Competitive relationship (for food, mates, etc.)

4. After many generations of offspring of the small birds on the island, describe how natural selection could lead to speciation and macroevolution. What would this do to the gene pool and allele frequency for the population of birds?

(Note: Scenario and questions adapted from Chapter 15 Active Learning Exercises from first edition of "Principles of Life" by Hillis)