The Mystery of Evolution: Why a Man Has Eyes in front?

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Why are our eyes not located on the sides of the head, but are looking forward? This is partly due to the need to perceive three-dimensional images, but the BBC Future correspondent discovered and other reasons.

Have you ever noticed that most animals in Zoo can be attributed to one of two groups? One eyes are on the sides of the head (these are hens, cows, horses, zebras), and others they are planted closer and located in front (in this group includes monkeys, tigers, owls and wolves). Zoo visitors themselves – people – obviously, belong to the second group. What is the reason for this difference?

The location of the eyes is always a compromise. When the eyes are in front, each of them sends to the brain an image with of one’s angle of view, and by overlaying these images on each friend of a person perceives depth. Animals with eyes located on the sides, not able to see the third dimension, but The review is much wider.

Probably, the arrangement of the eyes was formed in different animals differently. For example, in some turtles, the eyes are on sides, but the brain processes visual information as if their eyes looked forward – perhaps this is due to the fact that when turtles pull their head under the shell, their eyes perceive light only in front, as if they are located in front heads. But why at our branch of the evolutionary tree – at primates – eyes in front? There are many explanations for this.

A photo from open sources

In 1922, the British ophthalmologist Edward Tricher Collins wrote about that early primates needed a vision that “would allow them to swing and accurately jump from branch to branch … grab food with your hands and bring it to your mouth. “Therefore, I decided scientist, in the process of evolution they have developed the ability to evaluate distance.

In subsequent decades, Collins hypothesis repeatedly revised and clarified, but its essence for a long time remained unchanged: in the process of evolution, the eyes of our ancestors moved forward to accurately estimate the distance at jumping from tree to tree. Price error in determining the distance between the trees was really considerable. “Payback for miscalculation there was a fall from a height of several meters to the ground, teeming with carnivorous animals, “wrote a specialist in 1991 visual psychotherapy Christopher Tyler.

The weak point of Collins hypothesis is that many animals that settle in trees, such as squirrels, have eyes located on the sides. Therefore, in 2005, an American biologist and anthropologist Matt Carthmill proposed another hypothesis based on Peculiarities of vision of predators, able to evaluate very well distance. According to Cartmill, this allows them to track down and to catch prey, be it a leopard crouching behind a gazelle, a hawk, claws of a hare, or one of the primates, grabbing from a branch some insect.

A photo from open sources

The scientist found this explanation very elegant, because it allowed us to understand other evolutionary changes characteristic of primates. For example, early primates in hunting relied on vision, and not to smell. Cartmill decided that the deterioration in smell was a side effect of rapprochement of the eyes: just for the nose and nerves, connecting it with the brain, there is not much space left – all the space was occupied by the eyes.

American neuroscientist John Allman picked up the hypothesis Cartmilla and finalized it based on information about nocturnal predators – after all, not all predatory animals have eyes located in front. In cats primates and owls they really are in front of the head, and in mongooses, goofy and flytraps – on the sides. Allman’s contribution to the development of this hypothesis consists in the assumption that such vision is necessary for those who hunt at night – for example, cats and owls – because in front of the eyes they perceive light better than to the sides. The early primates just hunted at night and perhaps it is because of this addiction to night hunting for all of them offspring, including humans, eyes located in front.

The American neuroscientist theorist Mark Changisi arose one more explanation. In 2008, he published in the Journal theoretical biology “(USA) article on” x-ray vision “, suggesting that the front eyes allowed our ancestors who lived in the forest, see through dense foliage and close interweaving branches.

A photo from open sources

The loud name “x-ray vision” comes from a curious phenomenon described by Changizi: “If you hold your finger in front of eyes in an upright position, fixing a look at some an object located behind the finger, two will enter the brain images of the finger, and both of them will be transparent. “Thus it turns out that a person can “see through” a finger, as with x-rays.

Pile of trees in the forest makes it difficult to see only large animals such as primates. Smaller ones, such as proteins, do not have such difficulties because their small head can easily squeeze between branches and leaves. Large animals who do not live in the forest, there are also quite enough eyes that located on the sides.

So the reason our eyes are in front is not yet installed. Each hypothesis has its own strengths and weaknesses. side. But no matter why we needed this vision – to jump from branch to branch, catch tasty bugs or see through the foliage – it is obvious that such an arrangement of the eyes connected with life among the trees.

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