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Diagram of a human eye; note that not all eyes have the same anatomy as a human eye. The mammalian eye can also be divided into two main segments: the anterior segment and the posterior segment. [10] The human eye is not a plain sphere but is like two spheres combined, a smaller, more sharply curved one and a larger lesser curved sphere.
The size of the eyes in mammals is relatively small; in humans, eye weight is 1% of the mass of the head, while in a starling it reaches 15%. Nocturnal animals (for example, tarsiers) and animals that live in open landscapes have larger eyes.
Almost all mammals have brown or darkly-pigmented irises. [33] In humans, brown is by far the most common eye color, with approximately 79% of people in the world having it. [34] Brown eyes result from a relatively high concentration of melanin in the stroma of the iris, which causes light of both shorter and longer wavelengths to be absorbed. [35]
This type of eye is common in mammals, including humans. The simplest eyes are pit eyes. They are eye-spots which may be set into a pit to reduce the angle of light that enters and affects the eye-spot, to allow the organism to deduce the angle of incoming light. [1] Eyes enable several photo response functions that are independent of vision.
[50] [51] The differences in color are mainly caused by higher levels of melanin in the skin, hair and eyes in males. [52] [53] In one study, almost twice as many females as males had red or auburn hair. A higher proportion of females were also found to have blond hair, whereas males were more likely to have black or dark brown hair. [54]
Hair colors can change well into puberty, as some genes aren't "switched on" until the hormones flood the body in adolescence. Eventually, usually in the 30s, human hair stops producing melanin ...
H. Harris, publishing in the British Journal of Dermatology in 1947, wrote Native Americans have the least body hair, Han Chinese people and black people have little body hair, white people have more body hair than black people and Ainu have the most body hair. [18] Anthropologist Arnold Henry Savage Landor described the Ainu as having hairy ...
The functioning of a camera is often compared with the workings of the eye, mostly since both focus light from external objects in the field of view onto a light-sensitive medium. In the case of the camera, this medium is film or an electronic sensor; in the case of the eye, it is an array of visual receptors.