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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.

269 page  Curriculum Supplement from NIH 5 lessons  Ideas about the role of evolution in medicine Investigating lactose intolerance and evolution evolutionary processes and patterns inform medicine Using evolution to understand influenza Evaluating evolutionary explanations

This indicates that the mutation originated in just one person who became the ancestor of all subsequent people in the world with blue eyes, according to a study by Professor Hans Eiberg and colleagues at the University of Copenhagen.

Euglena and eyespots explained