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Do You See What Eye See?

Eye Evolution and Development


Conrad Toepfer
Division of Mathematics & Natural Sciences
Brescia University


A common misconception is that Darwin suggested that something as complex as the eye could not have evolved through natural selection. While the misunderstanding often comes from an incomplete reading of his argument, we have long known that intermediate varieties of eyes (e.g., eyespots, cupped eyes, and complex camera-type eyes) exist in a variety of organisms. Eyes are so common that it was thought that they had evolved independently 40–60 times. More recent molecular work, however, has identified the role of Pax6 genes and their homologs in the formation of eyes during development. The basic information for eye formation appears to have been present in the common ancestor to all bilaterans, and perhaps may be more ancient than that. This interrupted case study examines the history of evidence for eye evolution from Darwin’s initial postulates, through evidence of multiple intermediate forms, concluding in an examination of Pax6 homologs. The case is primarily for an introductory biology class but an additional section would be appropriate for upper-level evolution or developmental biology courses.


  • Recognize the existence of intermediate stages of the evolution of complex eyes.
  • Apply the concept of homology in the context of gene sequences.
  • Generate and test a hypothesis about Darwin's tenet of descent with modification from ancestral conditions using gene sequences and a cladogram.
  • Explain how a conserved Hox gene can result in the production of two different kinds of eyes and why this is support for common ancestry.


evolution; eye; developmental biology; homology; descent with modification; Darwin, Pax6; Hox gene; homeotic; homeobox; complex organ; homology

Topical Areas


Educational Level

Undergraduate lower division, Undergraduate upper division



Type / Methods

Flipped, Interrupted



Subject Headings

Developmental Biology  |   Evolutionary Biology  |  

Date Posted


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The following video(s) are recommended for use in association with this case study.

  • Genetic Toolkit
    This video discusses homeobox genes, a set of genes that produce basic body parts in all animals, beginning with Walter Gehring’s 1994 discovery of the eyeless gene, which guides the formation of fruit fly eyes. Running time: 4:23 min. Produced by PBS.
  • Evolution of the Eye
    Evolutionary biologist Richard Dawkins discusses the evolution of the eye. Running time: 7:55 min. Produced by the BBC.