Why Do Piloses Have Thinner Trunks Nowadays?
A trait variant can be beneficial, harmful, or neither to an individual. A beneficial trait variant makes it more likely an individual will be healthy, survive, and have many offspring. Over many generations, the beneficial trait variant will become more common. This process is called natural selection.
Students hear a story about animals called piloses in which the proportion of individuals in a population with thinner trunks increases over many generations. They reason about the sequence of events involved in the change. The class agrees on a framework called the 6 Key Steps that they might be able to use to explain how any animals and plants could change over time.
Materials to Have Ready
For each student:
Notebook page 9
A set of story strips (black text)*
A set of labels that highlight the key steps in natural selection (blue text)
For the class:
The class-wide 6 Key Steps Poster**
*L1-L7 teachers will need to cut out a set of story strips and key steps for each student by printing and cutting the PDF labeled "Story Steps and Key Strips," attached below.
**Provided by the EM Team for both L1-7 and L1-12 teachers