Homologous Structures: Evidence for Evolution

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SWBAT apply scientific ideas to construct an explanation for how homologous structures can be used to infer evolutionary relationships between fossil and modern organisms.

Big Idea

Students explore homologous structures as a source of evidence for evolution.


10 minutes

To engage students in lesson I show students How did feathers evolve? video by TEDEd.  The video addresses the evolutionary relationship between modern birds and dinosaurs due to discovered anatomical similarities, which is the topic of this lesson. (MS-LS4-2. Apply scientific ideas to construct an explanation for the anatomical similarities and differences among modern organisms and between modern and fossil organisms to infer evolutionary relationships.) 

In addition, the majority of my students are naturally drawn to anything that has to do with dinosaurs, as a result this engages students in the lesson! 

Students are required to answer the following questions as they watch the video:

1.  What's an anatomical detail that some dinosaurs share with birds (that no other animal does)?

a.  scales

b.  beaks

c.  wishbones

d.  eggs


2.  Dinosaurs used feathers to fly.

a.  True, flying dinosaurs sometime reached the size of small airplanes.

b.  False, dinosaurs weren't coordinated enough to fly.

c.  True, feathers are delicate but supported dinosaurs at heights up to 1,000 feet.

d. False, dinosaur arms were too short to support flight.


3.  What's the use of a peacock's tail feathers?

a.  To attract a mate.

b.  They help it fly longer distances.

c.  Peacocks use their tails to swim.

d.  They sweep small bugs into piles, making it easier to eat.


4.  What does Zimmer mean by accident of physics?

a.  Feathered dinosaur arms may have allowed dinosaurs to run faster uphill and glide short    distances after jumping.

b.  The advantages dinosaurs with feathered arms could have led to a natural selection of longer, feathered dinosaur arms.

c.  The intention of the feathers most likely started as one thing and shifted to a completely different thing (the lift created from the feathers was an accident of physics).

d.  All of the above.


5.  Approximately how long did it take from the time the first feather evolved until the first animal took flight?

a.  1 million years

b.  100,000 years

c.  50 million years

d.  500 years  


25 minutes

In this section of lesson students explore homologous structures and their significance as evidence for evolution by visiting Hand it to the Animals - Identifying X-rays from the zooa Simple Science website. Students use a program called WebImage to examine X-rays of animal hands in more detail to compare their structures. Based on the morphology, or shape, of the hand, your assignment will be to figure out its function and owner. (SP4 Analyzing and Interpreting Data)

Learning Objective:  Students learn about homologous structures, which are anatomical structures that have a similar relative location, structure, or appearance but are not necessarily similar in function.  

As students complete the module, they complete a Lab Data Sheet.

Teacher Note: Students might have difficulty in completing questions 8 and 9 in the module. It's important for students to read descriptions carefully before deciding on the correct match pairing. I particularly like these challenging questions because it addresses the relationship between structure and function. (CCC- Structure and Function).


10 minutes

Students now deepen their understanding by reading a text titled Living Species from cK-12.  

The Text discusses:

  • Comparative Anatomy 
    • Homologous Structures
    • Analogous Structures
  • Comparative Embryology 
  • Vestigial Structures
  • Comparing DNA

To reinforce the reading, I show students the video Homologous Structures by Math and Science:

Students answer the following questions after completing reading (WHST.6-8.9Draw evidence from informational texts to support analysis, reflection, and research.)


  1. Compare homologous and analogous structures.
  2. Humans and apes have five fingers they can use to grasp objects. Do you think these are analogous or homologous structures? Explain.


10 minutes

In this section students elaborate on what they have learned by visiting Similarities and differences: understanding homology and analogy on the Understanding Evolution website by the University of California, Berkeley.  By completing the Similarities and differences modulestudents further their understanding of homologous structures through comparisons with analogous structures.  

Once students have finished the module, they answer the following questions:

  1. Distinguish between homology and analogy.
  2. How are tetrapod limbs similar to each other?
  3. Give four examples of homologous tetrapod limbs.
  4. Give an example of a homologous structure in insects.
  5. What can happen to homologous structures of different species over time?
  6. Why are tetrapod and octopus limbs not homologous?


5 minutes

We close with an exit slip to assess student understanding.


Exit Slip:

Using the figure above explain what homologous structures are.  Specifically explain how homologous structures are used as a source of evidence to infer evolutionary relationships between modern and fossil organisms.  You may cite evidence from other sections of lesson to construct your explanation.

(SP6 - Constructing Explanations/WHST.6-8.2 -Write informative/explanatory texts to examine a topic and convey ideas, concepts, and information through the selection, organization, and analysis of relevant content.) 

Student Requirements:

Students use the CER Graphic Organizer and Transition Words to construct their scientific explanation.