Natural Selection

Evolution: Teachable Tidbit• Context:

• Introductory biology for science majors • 2 full class periods and a follow-up exam question

• Learning Goal: We want students to understand that natural selection is a phenomenon that applies to their lives

• Learning Outcomes: • Students will be able to describe and list the steps of natural

selection• Students will be able to attribute anthropogenic influences

on the environment to natural selection events• Students will be able to explain MRSA infections in terms of

natural selection

• Diversity: multiple learning styles and assessments

• 1st lecture—background information (Darwin & Natural Selection)Steps for natural selection to occur:1. There are variations in traits of individuals, and these variations

are heritable 2. There is selection pressure due to a change in the environment3. Some individuals survive longer and reproduce more4. There is change in the frequency of traits within the population

over time

• 2nd lecture—formative assessment

• Future lecture—population genetics, genetic drift, gene flow, etc.

• Unit exam – Summative question

Unit Timeline

Rats and Humans

The name warfarin stems from the acronym WARF, for Wisconsin Alumni Research Foundation + the ending -arin indicating its link with coumarin, the base chemical.

Rodent Population Control

Time

Resistant Individuals Through Time

What are the steps of natural selection?

• By yourself:– Think of the steps in natural selection– Write the steps involved in natural selection• 1 step per 3x5 index card

Steps in natural selection, cont.

• With a partner:– Discuss the steps of natural selection– What element of the rat scenario corresponds to

each step?

Clicker Question

• Is Warfarin resistance in rats an example of natural selection?A. YesB. No

Clicker Question

• In this example, humans apply the selection agent.

• Is Warfarin resistance in rats an example of natural selection?A. YesB. No

Clicker Question

• Does warfarin cause the resistance in rats?A. YesB. No

Summative Assessment

Of the following two situations, one or both is an example of natural selection in action. a. List the steps of natural selection.b. For each scenario, identify the elements matching the steps of natural selection.c. For each scenario, decide whether or not it is an example of natural selection and justify your answer.

Scenario 1R. Koch’s best friend, Chuck, just returned from Student Health Services; he’s just been told he has a MRSA infection. The doctor at Student Health Services gave Chuck a prescription for antibiotics and strict instructions to complete the entire course of antibiotics. Staphylococcus aureus is the SA in MRSA and is a bacteria routinely found on human skin and mucous membranes. Overtime, SA has become resistant to the common antibiotic methicillin, hence the MR (methicillin resistant) in MRSA.

Scenario 2Jane’s mom and dad can both roll their tongues into a U shape, but Jane can’t. Her two brothers, Dan and Kevin, can also roll their tongues and always teased Jane mercilessly. Most of Jane’s nieces and nephews can roll their tongues too. Jane’s husband can roll his tongue and so can their three children. Kevin’s wife just had a new baby and the family is eagerly awaiting the opportunity to challenge the new family member to roll her tongue!