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The human eye, showing the iris and pupil. In 1802, philosopher William Paley called it a miracle of "design."In 1859, Charles Darwin himself wrote in his Origin of Species, that the evolution of the eye by natural selection seemed at first glance "absurd in the highest possible degree". [3]
The evolution of color vision in primates is highly unusual compared to most eutherian mammals. A remote vertebrate ancestor of primates possessed tetrachromacy, [1] but nocturnal, warm-blooded, mammalian ancestors lost two of four cones in the retina at the time of dinosaurs.
Several layers such as the neural tube, neural crest, surface ectoderm, and mesoderm contribute to the development of the eye. [2] [3] [4] Eye development is initiated by the master control gene PAX6, a homeobox gene with known homologues in humans (aniridia), mice (small eye), and Drosophila (eyeless). The PAX6 gene locus is a transcription ...
The frontal eye, which expresses the PAX6 gene, has been proposed as the homolog of vertebrate paired eyes,or the pineal eye on vertebrates, the pigment cup as the homolog of the RPE (retinal pigment epithelium), the putative photoreceptors as homologs of vertebrate rods and cones, and Row 2 neurons as homologs of the retinal ganglion cells. [60]
The heads of vertebrates are complex structures, with distinct sense organs for sight, olfaction, and hearing, [12] and a large, multi-lobed brain protected by a skull of bone or cartilage. [13] Cephalochordates like the lancelet ( Amphioxus ), a small fishlike animal with very little cephalization, are closely related to vertebrates but do not ...
Responsible for this process in mammals is the visual sensory system, the foundations of which were formed at an early stage in the evolution of chordates. Its peripheral part is formed by the eyes , the intermediate (by the transmission of nerve impulses ) - the optic nerves , and the central - the visual centers in the cerebral cortex .
A newfound fossil of a jawless fish is the oldest known vertebrate cranium preserved in 3D. The 455 million-year-old find could illuminate how vertebrate heads evolved.
The parietal eye is found in the tuatara, most lizards, frogs, salamanders, certain bony fish, sharks, and lampreys. [7] [8] [9] It is absent in mammals but was present in their closest extinct relatives, the therapsids, suggesting that it was lost during the course of the mammalian evolution due to it being useless in endothermic animals. [10]
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