Tuesday, April 14, 2009
The Evolution of Eyes
Starting on pg 193, Sean Carroll first describes how there are many organisms, particularly in the Great Barrier Reef, that all have very specific structures. Some examples of what I mean are "the turtle's shell, the octopus's tentacles, and the crab's claws" (194). Its very possible that one can theorize that evolution has selected these particular structures because those structures are advantageous to those organisms. However, one point of contention comes up when discussing the eyes of each of those organisms. Is it possible that evolution is the reason for so many different eye-type variations of different organisms, or do the variations of eyes stem just a repeated mixing of scratch materials? Also tie into your response how the theme of heritable information pertains to this question.
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Whether these eyes developed from completely new structural lines or just were "repeating mixing of scratch materials" is a very confusing concept. In fact, I am not sure what exactly the prompt is asking, if you could restate it using more biology terms it would be easier to understand.
ReplyDeleteIn any case, eyes evolved in organisms in a variety of ways, depending on what selective pressures were put on the organisms and based on the random mutations in the genome. The offspring inherited this information and as each generation passed, more and more mutations caused further evolution of the eyes.
Carroll shows on p195 that while the eyes of humans, mice, and fruit flies are very different in structure, the Pax6 eyebuilding genes in each of these three organisms are very similar or nearly identical. This suggests that all eyes originated from a single, ancient organism. This ancestor probably evolved an eye by chance mutations. From that point, different selective conditions in varied habitats caused that ancestor to diverge into separate species, each one with eyes better adapted for their individual habitats.
ReplyDeleteOver time, as the tree of life expanded, the eyes of different organisms gradually became more and more specialized due to (as Sam stated,) natural selection acting on mutations that changed the eyes' genetic coding.
I like to believe this, but the origins of eyes are nebulous. It may be possible that two totally different ancestors evolved eyes on their own, and the tree of life went on from there. A lot of organisms have very similar eyes, but chances are, these organisms' eyes all evolved to achieve similar ends.
Evolution is definitely the reason behind the variety of eye types: chance mutations may make an organism's eyes better at seeing than another of that same species. From there, natural selection would choose the organism with the mutated eyes. What makes an eye better differs depending on the species. Flies are small and easily become prey: their compound eyes are very effective at sensing motion, and are thus well-suited to the dangerous life of a fly.