A 2-week introductory unit for 8th-grade science based on the OpenSciEd Unit 8.1 framework. Students investigate the real-world anchoring phenomenon of cliff swallows adapting to highway overpasses to discover how populations change over time. Through data analysis, physics-of-flight models, and population simulations, students build a consensus model of natural selection.
When called on, stand up, read your question clearly, and explain why it helps us solve the mystery.
STEP 3
Categorize
Place your note near similar questions. We will group related questions and draw lines between them.
Example: "Did the cars change, or did the birds change?"
Our Next Step Slide 6 of 6
Is there a physical difference?
To test if the birds themselves have changed over 30 years, researchers gathered and measured physical bird specimens.
Tomorrow, we will analyze actual historical wing-length data to see if the survivors look different from the roadkill victims.
Get ready to inspect real bird wing data in Lesson 2!
Section 1 Data Trends: "What differences do you observe between the roadkill and survivor data?"
Correct Answer: The roadkill birds had a much larger average wing length (about 111-112mm) than the survivors (about 106-107mm). This means birds with longer wings are dying on the roads at much higher rates than birds with shorter wings.
Section 2 Flight Lab: "Why does wing size affect a bird's ability to dodge a car?"
Correct Answer: Shorter, wider wings produce high instant lift. This allows a swallow to launch vertically off the ground much quicker when a car approaching at 65 mph threatens them. Long wings require longer runways and are less maneuverable.
Section 4 Final Model: "Why did the overall population's average wing size shrink over 30 years?"
Correct Answer: Cars on highways created a selective pressure. Birds with long wings were hit and killed, so they died before they could reproduce. Birds with short wings avoided cars, survived, and passed their short-wing genes to their babies. Over generations, short wings became the dominant trait.
Final Explanation Grading Rubric (NGSS MS-LS4-4)
Criterion
Exceeds Standards (3 pts)
Meets (2 pts)
Developing (1 pt)
Claim & Evidence
Clearly claims that wing length is hereditary and shifts due to differential survival. Cites specific measurements.
States that short wings survived cars better. Mentions data loosely.
Vague claim. No mention of wing-length numbers or trends.
Mechanism of Selection
Connects flight physics (vertical takeoff lift) with environmental pressure (speeding cars) as the cause of selective death.
Mentions cars kill long-winged birds but omits mechanical/takeoff explanation.
Mentions birds "learned" to dodge cars or "wanted" shorter wings.
Heredity & Generations
Explains that survivors reproduce and pass short-wing alleles to offspring, causing a population shift over multiple generations.
States that babies have short wings because parents did, but skips population context.
Thinks changes happened to individual birds during their lives.
Unit 8.1: Natural Selection & Common Ancestry Page 2 of 2 OpenSciEd Aligned Curriculum
heritable trait
If long-winged birds die before breeding, those long-wing genes disappear from the gene pool. Short-winged parents have short-winged chicks.
The Heredity Chain
Environmental Shift: Concrete overpasses + high speed traffic.
Differential Death: Long-winged birds hit by cars at high rates.
Allele Shift: Short-wing genes dominate breeding pool.
This is the scientific definition of Natural Selection.
Consensus Model Slide 6 of 6
Explaining the Mystery
We now have all the evidence we need. Let's build our final consensus model to explain how the swallow population adapted.
Your final task: Write a robust, evidence-backed scientific explanation on Page 2 of your worksheet. Use our key vocabulary: trait variation, selective pressure, heritability, and differential survival.
Let's compile our ideas and write our final scientific arguments!
Write Your Explanation Here (Minimum 2 paragraphs)
Unit 8.1: Natural Selection & Common Ancestry Page 2 of 2 OpenSciEd Aligned Curriculum
