Evidence of Common Ancestry Explorer: Investigating Evolutionary Relationships

Estimated Time: 45-60 minutes Materials: Internet-connected device, Evidence of Common Ancestry Explorer simulation, student handout.

Part 1: Engage (Anchoring Phenomenon)

Look closely at the skeletal structures of different animals, such as humans, mice, chickens, and chimpanzees. You might notice that despite their vastly different external appearances and functions (grasping, running, flying), the basic structure of their forelimbs contains similar bone arrangements (e.g., humerus, radius, ulna, and digits).

Discuss and Brainstorm:

Why might animals with such different lifestyles and physical appearances share similar underlying bone structures?
If we looked closer, down to the molecular level (DNA and proteins), would we see similar patterns of similarities and differences?
What questions do you have about how scientists determine how closely related different species are?

Part 2: Explore (Simulation Investigation)

You will use the Evidence of Common Ancestry Explorer simulation to compare four species: Human, Chimpanzee, Mouse, and Chicken. You will analyze multiple lines of empirical evidence: DNA sequences, Amino Acid sequences, and Anatomical Homology.

Step-by-Step Instructions:

Access the Simulation: Open the Evidence of Common Ancestry Explorer simulation.
Select Species: Use the drop-down menus to select “Species A” and “Species B” for comparison.
Analyze DNA Sequences:
- Click the “DNA Sequence (CYTB)” tab.
- Compare the DNA sequence of Cytochrome b between the two selected species.
- Observe the differences highlighted in red.
- Record the “DNA Match” percentage and the total number of “Differences” in the data table below.
Analyze Amino Acid Sequences:
- Click the “Amino Acid (Cytochrome C)” tab.
- Compare the amino acid sequence between the same two species.
- Note any differences. Pay attention to the fact that the simulation compares amino acids from a different protein (Cytochrome c) than the DNA gene (Cytochrome b). Consider how the match percentages for amino acids compare to those for DNA across the same species pair.
- Record the “Amino Acid Match” percentage in the data table.
Analyze Anatomical Homology:
- Click the “Anatomical Homology” tab.
- Compare the forelimb bone structures (humerus, radius, ulna, digits).
- Note the structural similarities despite any differences in size or shape.
- Personal Reflection: Briefly write down your initial thoughts on why these animals might share these bone structures.
Repeat: Repeat steps 2-5 for all possible pairs listed in the data table.

Data Collection Table

Species Pair	DNA Match (%)	DNA Differences (count)	Amino Acid Match (%)	Anatomical Observations
Human vs. Chimpanzee
Human vs. Mouse
Human vs. Chicken
Chimpanzee vs. Mouse
Chimpanzee vs. Chicken
Mouse vs. Chicken

Part 3: Explain (Sensemaking)

Using the data you collected in the Explore phase, answer the following questions to make sense of your observations.

Patterns in DNA: Which species pair had the highest percentage of DNA match? Which pair had the lowest? What does this suggest about how recently they shared a common ancestor?
DNA vs. Amino Acids: Did you observe any instances where the DNA sequences had differences, but the amino acid sequences were identical or had a higher match percentage? How is this possible given that the simulation compares DNA from the Cytochrome b gene with amino acids from the Cytochrome c protein? (Hint: Think about how different proteins might evolve at different rates due to their functional importance.)
Anatomical Evidence: How do the similarities in the forelimb bone structures support the idea of a shared evolutionary history, even when the bones are used for different purposes (e.g., a human arm vs. a chicken wing)?
Synthesizing Lines of Evidence: Do the patterns observed in the DNA sequences align with the patterns observed in the amino acid sequences and anatomical structures? Explain why having multiple lines of evidence is important in science.

Part 4: Elaborate/Evaluate (Argumentation & Modeling)

Constructing a Scientific Argument

Based on the patterns of similarity you observed in the data (DNA, Amino Acids, Anatomy), construct a scientific argument explaining how this empirical evidence supports the theory of common ancestry and biological evolution.

Your argument should:

Claim: State a clear conclusion about the evolutionary relationships among the four species (Human, Chimpanzee, Mouse, Chicken).
Evidence: Cite specific data from your investigation, including at least two different formats (e.g., quantitative DNA match percentages, qualitative anatomical comparisons).
Reasoning: Explain why the evidence supports your claim. Discuss how genetic information (DNA and amino acid sequences) and anatomical structures change over time and how similarities provide evidence of common descent from shared ancestors.

Extension Options

Phylogenetic Trees: Have students use the data they collected to draw a simple phylogenetic tree representing the evolutionary relationships between the four species.
Research Other Genes: Ask students to research why certain genes like Cytochrome C or Cytochrome b are commonly used in evolutionary studies (e.g., they are highly conserved and essential for cellular respiration).

Teacher Notes

NGSS Alignment

This task is aligned to the following dimensions of the Next Generation Science Standards (NGSS):

Performance Expectation: HS-LS4-1. Communicate scientific information that common ancestry and biological evolution are supported by multiple lines of empirical evidence.
Science and Engineering Practice (SEP): Obtaining, Evaluating, and Communicating Information. Students communicate scientific information (about phenomena and/or the process of development) in multiple formats (including orally, graphically, textually, and mathematically).
Disciplinary Core Idea (DCI): LS4.A: Evidence of Common Ancestry and Diversity. Genetic information, like the fossil record, provides evidence of evolution. DNA sequences vary among species, but there are many overlaps; in fact, the ongoing branching that produces multiple lines of descent can be inferred by comparing the DNA sequences of different organisms. Such information is also derivable from the similarities and differences in amino acid sequences and from anatomical and embryological evidence.
Crosscutting Concept (CCC): Patterns. Different patterns may be observed at each of the scales at which a system is studied and can provide evidence for causality in explanations of phenomena.

Evidence Statement Mapping

Student work will demonstrate the following evidence statements for HS-LS4-1:

1.a. Communication style and format: Students use at least two different formats (textual argument, quantitative data table, graphical/anatomical analysis) to communicate scientific information that common ancestry and biological evolution are supported by multiple lines of empirical evidence.
2.a.i. Connecting the DCIs and the CCCs (DNA): Students identify and communicate evidence derived from DNA sequences, noting how they vary among species but have many similarities (e.g., comparing human and chimpanzee vs. human and chicken DNA matches).
2.a.ii. Connecting the DCIs and the CCCs (Amino Acids): Students identify and communicate evidence of similarities in patterns of amino acid sequences, even when DNA sequences are slightly different (e.g., observing identical Cytochrome c amino acid sequences for human and chimpanzee alongside Cytochrome b DNA differences, indicating different evolutionary rates).
2.a.iv. Connecting the DCIs and the CCCs (Anatomy): Students identify and communicate anatomical evidence, such as the homologous structures in the forelimbs of humans, mice, chickens, and chimpanzees.