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  Topic: The Blind Leading the Blind, Berlinski on Eye Evolution< Next Oldest | Next Newest >  

Posts: 319
Joined: May 2002

(Permalink) Posted: July 03 2003,07:15   

I think that I just might write another letter to Commentary.  

E.g., regarding Berlinski's assertion about lancelets not having eyes, this is a matter of definitions.  There are so many variations on light-sensing organs in biology that there is essentially a continuum of complexity, and drawing a line somewhere to delineate "eyes" and simpler light-sensing organs is essentially arbitrary.  This in itself is a significant point in favor of the thesis that gradual evolution can produce eyes.  

Lancelets have light-sensing pigmented pits with nerves (which come into the pit from the top, BTW, in a similar fashion to the backwards retina of vertebrates), corresponding to the early stages of Nilsson and Pelger's proposed evolutionary sequence, all of which Berlinski was perfectly happy to call "eyes" in the rest of his essays and responses.

Scientists appear to be happy to use the term "eye" for lancelet sensory organs:


Amphioxus (Glardon et al., 1998), which represents the invertebrate chordates most closely related to vertebrates, shows Pax6 expression in the lamellar organ and the frontal eye which are the presumed homologues of the vertebrate pineal eye and paired eyes, respectively. The underlying embryonic plan from which mammalian eyes develop may therefore have been in place since the lower Cambrian period. (Hill, Robert E and Hammond, Katherine L (June  1999 ) Eye Development: Gene Control. In: Nature Encyclopedia of Life Sciences. London: Nature Publishing Group.   [doi:10.1038/npg.els.0000735])

Perhaps Berlinski was pointing out that lancelets have a single eye per organism rather than "paired sensory organs", but I think it's more likely that he mis-read a reference on lancelets and took a sentence that said that cephalochordates lacked bones and "paired sensory organs" and took it to mean that they lacked eyes entirely.  This would be just another in a long line of amateurish biological mistakes that Berlinski has made in this series.

  17 replies since April 04 2003,23:50 < Next Oldest | Next Newest >  


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