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Homology and Convergence in the Evolution of the Eye

By Jeff Bessen

From the author, Jeff Bessen:

Evolution is my favorite topic in all of biology, so when I was offered the chance to write a review paper on the topic of evolution or ecology for Dr. Kicklighter's class, the choice was a no-brainer. I chose to write about the evolution of the eye for several reasons. First, Charles Darwin himself saw the eye as a potential challenge to his nascent theory of evolution, and spent several paragraphs in The Origin of Species treating a hypothetical scenario of its evolution. Additionally, advocates of 'intelligent design' have frequently turned to the amazing complexity of the eye as a challenge to Darwin's theory. While evolution is uncontroversial among nearly every competent scientist, I wanted to educated myself about the current literature on how the eye evolved, and to what extent the great diversity of animal eyes have evolved independently. What I found was a surprisingly complicated narrative. Evolution can, and has, acted on many different aspects of the eye: photoreceptors, pigments, phototransduction pathways, and transcriptional regulation of eye development. Homologies between eyes exist at each of the above levels, implying some level of evolutionary relation and conservation. However, the two types of photoreceptors found in all animal eyes are unrelated, and several other features of eyes are, though similar, more likely the product of convergence than common ancestry. Therefore, any proposal regarding the evolutionary history of the eye must take into account the rich and complex literature on the subject.

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