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How Eyes Evolved – Analyzing the Evidence

Human eye and octopus eye with lens and retina

This analysis and discussion activity focuses on two questions. How could something as complex as the human eye or the octopus eye have evolved by natural selection? How can scientists learn about the evolution of eyes, given that there is very little fossil evidence?

To answer these questions, students analyze evidence from comparative anatomy, mathematical modeling, and molecular biology. Students interpret this evidence to develop a likely sequence of intermediate steps in the evolution of complex eyes and to understand how each intermediate step contributed to increased survival and reproduction.

The Teacher Notes suggest additions to the Student Handout that can be used to introduce concepts such as the role of gene duplication in evolution and/or homology and analogy. 

The Student Handout is available in the first two attached files and as a Google doc designed for use in online instruction and distance learning. (For additional instructions, see, especially item 7.) The Teacher Notes, available in the last two attached files, provide instructional suggestions and background information and explain how this activity is aligned with the Next Generation Science Standards and the Common Core State Standards.

eye evol SHO.docx2.51 MB
eye evol SHO.pdf610.55 KB
eye evol TN.docx1.13 MB
eye evol TN.pdf428.28 KB


iwaldron's picture

2022 revision

The biggest change in the Student Handout has been the addition of a question asking the students to develop a scientific argument for a claim that summarizes the information presented. Additional revisions clarify the Student Handout and Teacher Notes.

iwaldron's picture

2020 revision

In this revision, I have reorganized and revised the explanations, figures and questions to clarify the main arguments and evidence about how complex eyes could have evolved by natural selection. 

iwaldron's picture

July 2016 Revision

This additional revision of the Student Handout has clarified the explanations and questions related to the evidence from comparative anatomy, the mathematical model, and the molecular evidence.

iwaldron's picture

2016 revision

I have revised and reorganized the Student Handout to improve clarity and focus on fundamental biological processes. I have also replaced some less important questions with an expanded and improved section on molecular evidence. The Teacher Notes have been extensively revised to improve the logical flow, to incorporate more sophisticated understanding of the evolution of the eye (especially at the molecular level), and include suggested optional questions topics such as the evolutionary roles of gene duplication and mutations in the regulatory DNA sequences that control gene expression.

iwaldron's picture

2015 revision

In the Student Handout, the questions have been revised and streamlined to clarify the logic of the evolutionary arguments and provide helpful scaffolding for student understanding. The revised Teacher Notes include additional suggestions for implementation and optional additional questions on topics such as the irreducible complexity argument.

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