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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]
In humans, the pupil is circular, but its shape varies between species; some cats, reptiles, and foxes have vertical slit pupils, goats and sheep have horizontally oriented pupils, and some catfish have annular types. [3] In optical terms, the anatomical pupil is the eye's aperture and the iris is the aperture stop.
The pupil of the human eye can range in size from 2 mm to over 8 mm to adapt to the environment. The human eye can detect a luminance from 10 −6 cd/m 2, or one millionth (0.000001) of a candela per square meter to 10 8 cd/m 2 or one hundred million (100,000,000) candelas per square meter.
Humans, other primates, and dogs have round (spherical) pupils, which are useful for general all-round vision. Cats, snakes, crocodiles, and alligators have vertical slits which are useful for ...
The iris consists of two layers: the front pigmented fibrovascular layer known as a stroma and, behind the stroma, pigmented epithelial cells.. The stroma is connected to a sphincter muscle (sphincter pupillae), which contracts the pupil in a circular motion, and a set of dilator muscles (dilator pupillae), which pull the iris radially to enlarge the pupil, pulling it in folds.
A human experimenter, observed by either a human infant, a gorilla, a bonobo, or a chimpanzee, did one of four actions: Tilted his head up while closing his eyes; Looked at the ceiling with his eyes while keeping his head stationary; Looked at the ceiling with his head and his eyes; Looked straight ahead without moving his head or his eyes
A belief that the eye "recorded" the last image seen before death was widespread in the late 19th and early 20th centuries, and was a frequent plot device in fiction of the time, to the extent that police photographed the victims' eyes in several real-life murder investigations, in case the theory was true.
On the other end of the spectrum, there are real-life photographs that look like they come straight out of a video game or movie scene. We've scoured the depths of the 'net to find the most gamey ...