>Contents>The Evolution of Eyes
Light is the ultimate source of earth's energy and serves as the premier source of information for many species. Indeed, since the beginning of biological evolution over 5 billion years ago, sunlight has fueled all organic life and defined biological time on earth. Light and the light/dark cycle have probably been the most important selective forces ever to act on biological organisms. One of the most remarkable consequences of light on earth has been the evolution of eyes that has made vision possible. At present, we do not know whether eyes arose once or many times, and, in fact, many features of eye evolution are still puzzling.
How did eyes evolve? Darwin, the great English naturalist who first brought the systematic explanatory power of evolution to bear on the bewildering biological complexity of our planet, felt that eyes offered a special challenge to evolutionary thinking because they are such '...organs of extreme perfection and complication...' (1859). He was quite explicit on this point, saying '...that the eye....could have been formed by natural selection seems, I freely confess, absurd in the highest possible degree'. More than a century later, with new insights that reach from molecular to macroscopic levels of analysis, new mysteries reinforce Darwin's prescient writing. We still have much to learn from the evolution of eyes, both about the existing eyes as well as the processes of evolution that produced them.
Current interest and excitement about eye evolution comes from discoveries at both ends of the full spectrum of biological investigation. Molecular biologists who seek fundamental similarities among organisms have found some genes implicated in eye development that are conserved in eyes from animals across a large phylogenetic distance. Evolutionary biologists interested in understanding why organisms and their parts are so different have found new types of eyes, both in the fossil record and in living animals. What do these different approaches to the evolution of eyes tell us? Together they offer complementary views of eye evolution and possibly the beginnings of a clear story. This article will examine features of eyes for clues about their origins.
The Evolution of Eyes
Why Do We See What We See?
How Do Eyes Work and How Did They Evolve?
How Do Eyes Capture Photons?
Where Do Lenses Come From?
Eyes: Convergence or Homology?
Conclusions
References
Biography
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