Posted: Mar 10, 2012 11:15 am
GenesForLife wrote:I have a little paper with me...ABSTRACT
The evolution of the eye is a matter of debate ever since Darwin’s Origin of Species.
While morphological comparisons of eye anatomy and photoreceptor cell types led to the view that
animal eyes evolved multiple times independently, the molecular conservation of the pax6 eyespecifying
cascade has indicated the contrary - that animal eyes evolved from a common, simple
precursor, the proto-eye. ...
Late comment: There is a common confusion here between imaging eyes and non-imaging eyes. When it is stated that "animal eyes evolved multiple times independently" it usually refers to imaging eyes evolving multiple times from the same non-imaging precursor. It is universally accepted that non-imaging light sensing only evolved once (with the first opsin), and that this occurred before animals even existed (cyanobacteria express opsins).
An example of the errors caused by assuming that imaging eyes only evolved once in the animal kingdom is the falsified hypothesis based on the universality of PAX6 in the animal kingdom, that vertebrate eyes evolved from, say imaging cepahalopod eyes, or even insect eyes. The reason for the error is the incorrect assumption that the presence of PAX6 implies an imaging eye - it does not, because PAX6 is expressed in various organs containing neurons, such as the pineal gland.