Homologous, Analogous, and Vestigial Structures

Homologous, Analogous, and Vestigial Structures

High School

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Learning Objectives

• Define and differentiate between homologous, analogous, and vestigial structures.

• Explain how homologous and vestigial structures provide evidence for divergent evolution.

• Describe how analogous structures are a result of convergent evolution.

• Identify examples of each type of structure and the evolutionary pattern they represent.

Key Vocabulary

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Homologous Structures

Organs in related organisms from a common ancestor that may not serve the same purpose.

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Analogous Structures

Structures with a similar function but are structurally different and do not share common origin.

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Vestigial Structures

Anatomical features or behaviors that no longer seem to have a purpose in an organism.

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Divergent Evolution

The process where related species evolve different traits over time, leading to new species.

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Convergent Evolution

A process where unrelated species independently evolve similar traits as a result of similar environments.

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What Are Homologous Structures?

• These are features shared by related species, inherited from a common ancestor.

• ​They have a similar underlying structure but are used for different functions.

• For example, a human arm, a whale flipper, and a bat wing.

• Homologous structures provide strong evidence for the process of divergent evolution.

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Solved Example 1
A researcher is comparing the wing of a bat and the flipper of a whale. They both have a similar underlying bone structure, inherited from a common ancestor. What type of structures are these?

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Step 1: Analyze and Sketch the Problem

• Goal: Identify the type of structure based on the description.

• Knowns: The bat wing and whale flipper have a similar bone structure from a common ancestor but are used for different functions.

• Unknown: The term for these types of biological structures.

• Formula: Not applicable for this conceptual problem.

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Solved Example 1
A researcher is comparing the wing of a bat and the flipper of a whale. They both have a similar underlying bone structure, inherited from a common ancestor. What type of structures are these?

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Step 2: Solve for the Unknown

• Homologous structures: Same origin, different function.

• Analogous structures: Different origin, same function.

• Vestigial structures: No longer have a function.

• The description matches the definition of homologous structures.

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Solved Example 1
A researcher is comparing the wing of a bat and the flipper of a whale. They both have a similar underlying bone structure, inherited from a common ancestor. What type of structures are these?

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Step 3: Evaluate the Answer

• The bat wing and the whale flipper are homologous structures.

• They provide evidence for divergent evolution, where related species adapt to different environments.

Multiple Choice

Which of the following best describes homologous structures?

• Structures that evolve independently in unrelated species to serve a similar purpose.

• Structures that are similar in anatomy and embryonic development due to a common ancestor, but may have different functions.

• Structures that have no function in an organism but were functional in an ancestor.

• Structures that have the same function but different anatomy, resulting from convergent evolution.

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Analogous Structures: Different Origin, Same Function

• These structures have similar functions but different anatomy and origins.

• They result from convergent evolution, not a shared recent ancestor.

• For example, the wings of birds, bats, and butterflies serve for flight.

• Sharks and dolphins have streamlined bodies but are not closely related.

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Solved Example 2
A car travels 434 km in 4.5 hours. What is its average speed?

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Step 1: Analyze and Sketch the Problem

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Solved Example 2
A car travels 434 km in 4.5 hours. What is its average speed?

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Step 2: Solve for the Unknown

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Solved Example 2
A car travels 434 km in 4.5 hours. What is its average speed?

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Step 3: Evaluate the Answer

• Check: 96.4 km/h * 4.5 h = 434 km.

• The answer is correct.

Multiple Choice

A shark (a fish) and a dolphin (a mammal) both have streamlined bodies and fins that help them swim. According to the text, what is this an example of?

• Vestigial structures that have lost their original function.

• Homologous structures resulting from a recent common ancestor.

• Analogous structures resulting from convergent evolution due to similar environmental pressures.

• Divergent evolution where two species become more different.

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What Are Vestigial Structures?

• Vestigial structures are body parts or reflexes with little to no current function.

• They are leftovers from an ancestor that once used these functional structures.

• Human examples include the tailbone (coccyx), the appendix, and wisdom teeth.

• The goosebump reflex is a vestigial reflex from our distant hairy ancestors.

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Multiple Choice

Based on the information provided, why is the human appendix considered a vestigial structure?

• It has little to no function in humans but was functional in an ancestor.

• It is an example of a structure that resulted from convergent evolution.

• It is a structure that has a similar function to organs in unrelated species.

• It is essential for modern human digestion.

Patterns of Evolution

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Divergent Evolution

• Related species evolve different traits when adapting to new environments.

• Species often share a recent common ancestor before diverging.

• Homologous and vestigial structures are evidence of this pattern.

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Convergent Evolution

• Unrelated species independently evolve features that appear similar.

• This happens when they adapt to similar environmental pressures.

• Analogous structures are a result of this evolutionary process.

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Parallel Evolution

• Two similar species evolve in the same direction together.

• They independently acquire similar characteristics over a period of time.

• Gliding frogs evolved in parallel from different tree frog species.

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Solved Example 3
A species of flightless bird, isolated on an island, is discovered to have a gene for feather development that is 98% similar to that of a mainland bird. What is the percent divergence in this gene?

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Step 1: Analyze and Sketch the Problem

• Goal: Find the percent divergence between the two bird species' genes.

• Knowns: The gene similarity is 98%.

• Unknown: The percent divergence.

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Solved Example 3
A species of flightless bird, isolated on an island, is discovered to have a gene for feather development that is 98% similar to that of a mainland bird. What is the percent divergence in this gene?

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Step 2: Solve for the Unknown

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Solved Example 3
A species of flightless bird, isolated on an island, is discovered to have a gene for feather development that is 98% similar to that of a mainland bird. What is the percent divergence in this gene?

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Step 3: Evaluate the Answer

• The percent divergence is 2%. This small difference indicates a close evolutionary relationship, which is consistent with the scenario of a bird population being recently isolated on an island.

• The answer is reasonable.

Multiple Choice

What is the key difference between divergent and convergent evolution?

• Divergent evolution leads to similar traits, while convergent evolution leads to different traits.

• Divergent evolution is a result of homoplasy, while convergent evolution is not.

• Divergent evolution involves related species developing different traits, while convergent evolution involves unrelated species developing similar traits.

• Divergent evolution involves unrelated species, while convergent evolution involves related species.

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Common Misconceptions About Evolution

Misconception	Correction
Similar structures and functions mean species are closely related.	They can be analogous structures that evolved independently.
Vestigial structures have an unknown or secret function.	They have lost most or all of their original function.
Evolution only results in adding new, complex traits.	Evolution can also cause the loss or reduction of traits.

Multiple Choice

How do homologous structures and vestigial structures both provide evidence for divergent evolution?

• They both demonstrate that species can lose traits but not gain them.

• They are both examples of structures that have the same function in different species.

• They both show that unrelated species can develop similar traits.

• They both indicate descent from a common ancestor, with modifications or reductions over time as species adapt to new environments.

Multiple Choice

A student observes that both bats and butterflies have wings for flight. Why would a scientist conclude that these wings are analogous structures and not homologous?

• Because the wings have different underlying anatomy and embryonic origins, indicating they did not come from a common ancestor with wings.

• Because bats and butterflies are both flying animals.

• Because wings are a common trait among many different types of animals.

• Because both species evolved from an ancestor that could fly.

Multiple Choice

Imagine a scenario where a species of cave-dwelling fish is discovered to have small, non-functional eye sockets. How would you use the concepts of vestigial structures and divergent evolution to explain this observation?

• The eye sockets are analogous structures to the eyes of other fish.

• The fish must have evolved from an ancestor that lived in light and had functional eyes, but lost eye function as it adapted to a dark cave environment.

• The fish's ancestors were blind, and the eye sockets are a new, developing feature.

• This is an example of convergent evolution, where the fish is becoming more like other cave-dwelling animals.

Multiple Choice

Cacti in the American desert and euphorbias in the African desert are unrelated, yet both have evolved succulent, water-storing bodies and spines. What is the best explanation for this similarity?

• They independently evolved these similar (analogous) traits as adaptations to survive in similar hot, dry environments, which is an example of convergent evolution.

• One plant learned to mimic the other to survive.

• They share a recent common ancestor that was succulent.

• This is an example of divergent evolution.

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Summary

• Homologous structures point to a common ancestor and divergent evolution.

• Analogous structures result from convergent evolution in unrelated species.

• Vestigial structures are evolutionary remnants that have lost their original function.

• Evolutionary relationships are traced using homologous, not analogous, structures.

Poll

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