what is the first step in the evolution of the eye
photoreceptor proteins that sense light eyespots
title: Eye development text: Eye development Eye formation in the human embryo begins at approximately three weeks into embryonic development and continues through the tenth week. Cells from both the mesodermal and the ectodermal tissues contribute to the formation of the eye. Specifically, the eye is derived from the neuroepithelium, surface ectoderm, and the extracellular mesenchyme which consists of both the neural crest and mesoderm. Neuroepithelium forms the retina, ciliary body, iris, and optic nerves. Surface ectoderm forms the lens, corneal epithelium and eyelid. The extracellular mesenchyme forms the sclera, the corneal endothelium and stroma, blood vessels, muscles, and vitreous. The eye begins to title: Evolution of the eye text: skulls for blood vessels and nerves to go through. All this adds to the growing amount of evidence that supports Darwin's theory. The first fossils of eyes found to date are from the lower Cambrian period (about ). The lower Cambrian had a burst of apparently rapid evolution, called the "Cambrian explosion". One of the many hypotheses for "causes" of the Cambrian explosion is the "Light Switch" theory of Andrew Parker: It holds that the evolution of eyes started an arms race that accelerated evolution. Before the Cambrian explosion, animals may have sensed light, but did not use it for title: Eye development text: There is some evidence that LMX1B plays a role in periocular mesenchymal survival. Eye development Eye formation in the human embryo begins at approximately three weeks into embryonic development and continues through the tenth week. Cells from both the mesodermal and the ectodermal tissues contribute to the formation of the eye. Specifically, the eye is derived from the neuroepithelium, surface ectoderm, and the extracellular mesenchyme which consists of both the neural crest and mesoderm. Neuroepithelium forms the retina, ciliary body, iris, and optic nerves. Surface ectoderm forms the lens, corneal epithelium and eyelid. The extracellular mesenchyme forms the sclera, the title: Eye development text: develop as a pair of optic vesicles on each side of the forebrain at the end of the 4th week of pregnancy. Optic vesicles are outgrowings of the brain which make contact with the surface ectoderm and this contact induces changes necessary for further development of the eye. Through a groove at the bottom of the optic vesicle known as choroid fissure the blood vessels enter the eye. Several layers such as the neural tube, neural crest, surface ectoderm, and mesoderm contribute to the development of the eye. Eye development is initiated by the master control gene Pax-6, a homeobox title: Evolution of the eye text: Evolution of the eye Many researchers have found the evolution of the eye attractive to study, because the eye distinctively exemplifies an analogous organ found in many animal forms. Simple light detection is found in bacteria, single-celled organisms, plants and animals. Complex, image-forming eyes have evolved independently several times. Complex eyes appeared first within the few million years of the Cambrian explosion. From before the Cambrian, no evidence of eyes has survived, but diverse eyes are known from the Burgess shale of the Middle Cambrian, and from the slightly older Emu Bay Shale. Eyes are adapted to the various requirements