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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.
Facial width to height ratio (fWHR) is a measure of the width of a person’s face compared to its height. [1] Research has shown that higher FWHR is associated with various physical and behavioral traits, such as adolescent testosterone, [ 2 ] aggression , [ 3 ] attractiveness to women, [ 4 ] cause of death by violence, [ 5 ] CEO success as ...
The face is the front of an animal's head that features the eyes, nose and mouth, and through which animals express many of their emotions. [ 1 ] [ 2 ] The face is crucial for human identity , and damage such as scarring or developmental deformities may affect the psyche adversely.
Human eye. The cooperative eye hypothesis is a proposed explanation for the appearance of the human eye. It suggests that the eye's distinctive visible characteristics evolved to make it easier for humans to follow another's gaze while communicating or while working together on tasks. [1] [2] [3]
The young human eye can change focus from distance (infinity) to as near as 6.5 cm from the eye. [32] [33] This dramatic change in focal power of the eye of approximately 15 dioptres (the reciprocal of focal length in metres) occurs as a consequence of a reduction in zonular tension induced by ciliary muscle contraction.