Evidence for Evolution and Phylogenetic Analysis Study Guide

Daily Learning Context and Agenda

Date: June 26, 2026

Daily Learning Goal: Students will be able to interpret evidence for evolution by text readings and figure analysis so they can support evolution as the change of species over time.

Agenda:

1. Introduction to Evolution

2. Evidence of Evolution

Reminders:

• Extra Credit Science Abstract is due at 9:00 AM on Monday, July 1.

Entry Task:

1. What is your favorite animal?

2. Why is this animal so interesting to you? What does/can it do that makes it different from other animals?

3. How does this animal survive in the environment that it lives in (compared to other environments)?

The Fundamental Principles of Evolution

The Unifying Principle:

• Evolution is considered THE unifying principle of biology.

• Evolution has produced the rich diversity of life that inhabits and changes the Earth.

• All life is related and changes over time — if it does not change, it becomes extinct.

• Evolution is supported by multiple lines of evidence.

Defining Evolution:

• Biological Definition: Evolution is the change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes that are passed on from parent to offspring during reproduction.

• Developmental Definition: Evolution is the process by which different kinds of living organisms have developed and diversified from earlier forms during the history of the earth.

Biological Diversity Feature: Thiomargarita magnifica

• Discovery: The largest bacterium ever discovered was found in the Caribbean Sea.

• Size Specifications:

  • Maximum size: approximately $2\,cm$.

  • It is about $50 \times$ the size of other giant bacteria.

  • It is about $5,000 \times$ the size of most other average-size bacterial species.

The Four Primary Lines of Evidence for Evolution

Through the investigation of POGIL (Process Oriented Guided Inquiry Learning) activities, four specific lines of evidence are identified and summarized:

1. Geology and the Fossil Record

• The Law of Superposition: Older layers of rock are always below newer layers. Consequently, younger fossils will be found in layers above older ones.

• Predictive Value: By looking at fossil records and comparing them to different formations, scientists can predict the age of fossils, rock formations, transition species, and various other geological markers.

2. Embryology

• Definition: Embryology is the study of the development of the single-celled embryo.

• Purpose: The goal is to observe similarities in species’ initial forms before specialization takes place.

• Identification: It serves as a way of identifying common ancestors and degrees of relation by comparing embryos through various stages of development across different species.

3. Homologous Structures

• Anatomy and Ancestry: Homologous structures of animal limbs are similar because of shared ancestry. However, they each have a different purpose depending on the animals’ specific environment.

• Evolutionary Drift: These structures show how species share similar but not identical traits. Over time, the purpose of the structures drifted apart from each other, which supports the concept of evolution and a generational path.

4. DNA Sequence Comparison

• Similarity Analysis: DNA sequence comparison shows high similarity between species, which suggests a common ancestor.

• Current Research: This evidence allows scientists to locate similar species existing today and investigate further research into evolutionary divergence.

Phylogenies and the Tree of Life

Constructing Phylogenies:

• Phylogenies are based on similarities in DNA.

• Scientists analyze the traits of species to determine which ones share a recent common ancestor.

• Tree Building: A tree is built to represent predictions of evolutionary relationships based on shared traits.

  • Example Trait Analysis: A set of organisms may all possess lungs. However, only specific branches (such as mice and chimpanzees) may possess fur and mammary glands, while other organisms in the set do not.

Key Concepts in Reading Phylogenetic Trees:

• Common Ancestor: Defined as one population that leads to the rise of two different species.

• Big Idea: All life on Earth (both current and past) is related to one another; we share common ancestry.

• Relatedness Questions: To interpret a tree, one must identify standard relationships, such as whether amphibians are more closely related to birds or fish, or if crocodiles are more closely related to birds or rabbits.

• Nodes: The points on the tree where branches split represent the most recent common ancestor (MRCA).

Comparative Anatomy: Homology vs. Analogy

Case Study: Thumb Structures

• Primates (Humans, Chimpanzees, Gorillas): These organisms share the origin of opposable thumbs, making them homologous traits across these species.

• Pandas: Pandas possess the origin of false "thumbs." In a cladogram, the panda thumb is considered ANALOGOUS to primate thumbs because it arose independently on a separate evolutionary path and did not come from the same common ancestor as the primate thumb.

Questions & Discussion

• Practice Opportunity: Students are encouraged to try the questions on Snorkl for more practice before the upcoming test.

• Inquiry on Relatedness: Who are the common ancestors of you and your cousin? Who are your most recent common ancestors?

Additional Activities and Assignments

1. Evidence of Evolution POGIL: Finish the activity and check work using the keys posted on Canvas. Note that the keys do not provide answers for every single question.

2. Video Lecture: Watch "Endless Forms Most Beautiful" by Dr. Sean Carroll. Use the Guided Notes sheet to organize ideas regarding the introduction to Charles Darwin and natural selection. Completed notes must be submitted to Canvas by Monday at 9:00 AM.

3. Textbook Reading: Review sections $13.1$ through $13.9$.

4. Extra Credit: Ecology Unit Extra Credit abstract is due Monday at 9:00 AM.