Can you please discuss the evolution of vertebrate eye atleast 3 paragraph. .ASAP
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Ever since Darwin, scientists have wondered about the evolution of eyes. The apparent perfect adaptation of distinct eye types to the large variety of organisms belies some interesting common principles that constrain evolution. Morphological comparisons suggested eyes were polyphyletic, evolving 40-60 different times. In contrast, comparison of development at the molecular level identified commonalities among molecules used to build eyes across many species, suggesting a monophyletic origin. Most of this work compared eyes based on ciliary photoreceptors found primarily in vertebrates with eyes based on microvillar photoreceptors found primarily in invertebrates. Both these eye types rely on rhodopsin (type 2) but have different transduction cascades. Recently, this controversy has been resolved with evidence that both primary eye types existed in ancestral bilaterians and are present in extant vertebrates and invertebrates. This means that at least these two eye types were present in the urbilateria, prior to the Cambrian explosive speciation. Moreover, this ancient origin is also true for an additional functional photodetection system, the cryptochromes that exist widely in both plants and animals. So the eyes we know are certainly phylophyletic in origin. In addition, there is a second family of photodetection found in archaea and eukaryotic microbes based on a family of rhodopsin molecules (rhodopsin 1) that arose through convergent evolution. The range of rhodopsin use in these organisms is just now being discovered but will likely yield more surprises about how to detect light. Finally, several additional families of opsin molecules have been identified though none are yet known to play any specific function.
Eight major types of optics in animal eyes. Both chambered eyes (top) and compound eyes (bottom) form images using shadows ( A and B ), refraction ( C to F ), or reflection ( G and H ). Light rays shown in blue, photoreceptive structures are shaded. The simple pit eye (A) (chambered nautilus) led to the lensed eyes in fish and cephalopods (C) (octopus) and terrestrial animals (D) (red-tailed hawk). Scallop eyes (G) (bay scallop) are chambered but use concave mirror optics to produce an image. The simplest compound eye (B) (sea fan) found in bivalve molluscs led to the apposition compound eye (E) (dragonfly) found in bees, crabs, and fruit flies; the refracting superposition compound eye (F) (Antarctic krill) of moths and krill; and the reflecting superposition eye (H) (lobster) found in decapod shrimps and lobsters. Diagrams modified by permission from ( 2 ). [Sources: (A) Wikipedia; (B) Robert Pickett/CORBIS; (C) Russell Fernald/Stanford University; (D) Steve Jurvetson/Wikipedia; (E) David L. Green/Wikipedia; (F) Gerd Alberti, Uwe Kils/Wikipedia; (G) Bill Capman/Augsburg College; (H) Lawson Wood/CORBIS]