Post by Seirscius on Sept 28, 2005 22:57:11 GMT -5
The cheesy title is absolutely necessary. Tonight at the "Ask an atheist" panel I claimed that eyes have evolved many times independently over the course of history.
This paper provides substantial evidence to support my claim:
www.biology.duke.edu/cunningham/pdfs/Oakley%20and%20Cunningham.pdf
Summarization: Either eyes have developed independently for certain groups of ostracids, or the trait was lost by all surrounding phylums but a few. Of course, if the compound eyes evolved from these phylums which lost their eyes, this is still independent evolution.
A second paper on the topic: www.lifesci.ucsb.edu/eemb/faculty/oakley/research/research.html
Illustrating current intermediate eye states:
"In fact, nature displays progressions of simple to complex visual structures (Ecker 1990:65-66), such that one can see how the eye could have evolved gradually."
-The Defender's Guide to Science and Creationism
A large piece from Ernst Mayr:
Sometimes common descent is strongly challenged by the data. Mayr recounts that “Photosensitive, eyelike organs have developed in the animal series independently at least 40 times…” (p. 205) It is incredible that such complexity would evolve “independently”—again, similarity implies ancestry, except for when it doesn’t. Even more significantly, Mayr finds that some of the same genes are used in eye construction despite the fact that these eyes supposedly evolved in completely separate lineages:
“It had been shown that by morphological-phylogenetic research that photoreceptor organs (eyes) had developed at least 40 times independently during the evolution of animal diversity. A developmental geneticist, however, showed that all animals with eyes have the same regulator gene, Pax 6, which organizes the construction of the eye. It was therefore concluded at first concluded that all eyes were derived from a single ancestral eye with the Pax 6 gene. But then the geneticist also found Pax 6 in species without eyes, and proposed that they must have descended from ancestors with eyes. However, this scenario turned out to be quite improbable and the wide distribution of Pax 6 required a different explanation. It is now believed that Pax 6, even before the origin of eyes, had an unknown function in eyeless organisms, and was subsequently recruited for its role as an eye organizer.” (p. 113)
Mayr attempts to give a plausible evolutionary explanation for why so many types of organisms use the same genes – through completely independent evolution – to construct eyes. However, given that this identical usage of the Pax 6 gene supposedly evolved so many (40+) times in evolutionary history, it almost appears that life was “pre-destined” to evolve eyes in this manner. Mayr recounts that this independent evolution is not uncommon:
“That a structure like the eye could originate numerous times independently in very different kinds of organisms is not unique in the living world. After photoreceptors had evolved in animals, bioluminescence originated at least 30 times independently among various kinds of organisms. In most cases, essentially similar biochemical mechanisms were used. Virtually scores of similar cases have been discovered in recent years, and they often make use of hidden potentials of the genotype inherited from early ancestors.” (p. 206-207)
According Richard Dawkins, enough time has elapsed for eyes to evolve 1500 times over within any single lineage. He uses conservative estimations for this, I add.
Wikipedia:
Despite the precision and complexity of the eye, computer models of eye evolution, developed by Dan-Erik Nilsson and Susanne Pelger, demonstrated that a primitive optical sense organ could evolve into a complex human-like eye within a reasonable period (less than a million years) simply through small mutations and natural selection.
D.-E. Nilsson and S. Pelger, Proc. R. Soc. London Ser. B 256, 53 (1994) states that the timeframe could be as low as 400,000 years.
I hope this information is convincing enough to validate my comment during the meeting.
Don
This paper provides substantial evidence to support my claim:
www.biology.duke.edu/cunningham/pdfs/Oakley%20and%20Cunningham.pdf
Summarization: Either eyes have developed independently for certain groups of ostracids, or the trait was lost by all surrounding phylums but a few. Of course, if the compound eyes evolved from these phylums which lost their eyes, this is still independent evolution.
A second paper on the topic: www.lifesci.ucsb.edu/eemb/faculty/oakley/research/research.html
Illustrating current intermediate eye states:
"In fact, nature displays progressions of simple to complex visual structures (Ecker 1990:65-66), such that one can see how the eye could have evolved gradually."
-The Defender's Guide to Science and Creationism
A large piece from Ernst Mayr:
Sometimes common descent is strongly challenged by the data. Mayr recounts that “Photosensitive, eyelike organs have developed in the animal series independently at least 40 times…” (p. 205) It is incredible that such complexity would evolve “independently”—again, similarity implies ancestry, except for when it doesn’t. Even more significantly, Mayr finds that some of the same genes are used in eye construction despite the fact that these eyes supposedly evolved in completely separate lineages:
“It had been shown that by morphological-phylogenetic research that photoreceptor organs (eyes) had developed at least 40 times independently during the evolution of animal diversity. A developmental geneticist, however, showed that all animals with eyes have the same regulator gene, Pax 6, which organizes the construction of the eye. It was therefore concluded at first concluded that all eyes were derived from a single ancestral eye with the Pax 6 gene. But then the geneticist also found Pax 6 in species without eyes, and proposed that they must have descended from ancestors with eyes. However, this scenario turned out to be quite improbable and the wide distribution of Pax 6 required a different explanation. It is now believed that Pax 6, even before the origin of eyes, had an unknown function in eyeless organisms, and was subsequently recruited for its role as an eye organizer.” (p. 113)
Mayr attempts to give a plausible evolutionary explanation for why so many types of organisms use the same genes – through completely independent evolution – to construct eyes. However, given that this identical usage of the Pax 6 gene supposedly evolved so many (40+) times in evolutionary history, it almost appears that life was “pre-destined” to evolve eyes in this manner. Mayr recounts that this independent evolution is not uncommon:
“That a structure like the eye could originate numerous times independently in very different kinds of organisms is not unique in the living world. After photoreceptors had evolved in animals, bioluminescence originated at least 30 times independently among various kinds of organisms. In most cases, essentially similar biochemical mechanisms were used. Virtually scores of similar cases have been discovered in recent years, and they often make use of hidden potentials of the genotype inherited from early ancestors.” (p. 206-207)
According Richard Dawkins, enough time has elapsed for eyes to evolve 1500 times over within any single lineage. He uses conservative estimations for this, I add.
Wikipedia:
Despite the precision and complexity of the eye, computer models of eye evolution, developed by Dan-Erik Nilsson and Susanne Pelger, demonstrated that a primitive optical sense organ could evolve into a complex human-like eye within a reasonable period (less than a million years) simply through small mutations and natural selection.
D.-E. Nilsson and S. Pelger, Proc. R. Soc. London Ser. B 256, 53 (1994) states that the timeframe could be as low as 400,000 years.
I hope this information is convincing enough to validate my comment during the meeting.
Don