Eyes evolved to have X-ray capacity

The advantage of using two eyes to observe has long been associated with our ability to see only three-dimensional images. A new study by a scientist at Rensselaer Polytechnic Institute has discovered the advantage of binocular vision: the ability to see through objects.

Most animals such as fish, insects, reptiles, birds, rabbits, and horses exist in uncomplicated and messy environments like grasslands, and their eyes are on the sides of their heads. The eyes are on both sides allowing the animal to observe the front and the rear, which is called the panoramic view.

Humans and large mammals such as primates and large mammals like tigers exist in complex environments (forests), so the eyes grow to look in the same direction. Animals with forward-facing eyes are incapable of looking behind, but in return they are able to see X-rays, according to Mark Changizi, professor of neuroscience at Rensselaer. selected to maximize visibility in dense environments like forests.

All animals have two-eye areas - the space where both eyes look at the same time - provides the ability to see X-rays and this area widens as the eyes look more forward.

Proving X-ray ability is quite simple: hold a pen in a vertical direction and look at something behind it. If you turn one eye at a time, you'll see in both cases, the pen covers your vision. However, if you open both you can look through the pen to observe the space behind.

Most animals have eyes facing both sides, allowing them to observe the whole scene around them, both in front and behind.(Photo: Rensselaer / Changizi)

To demonstrate how our eyes can see through a lot of clutter, point all your fingers in random directions, then pay attention to the space outside you can look with one eye and two eyes.You miss a lot of things when you look with a cool one, but you can see almost everything with two eyes.

Changizi, the project's chief investigator, said: 'The two-eye view area is like the' spotlight 'that lights up behind the obstacle, allowing us to get rid of the area blocked by eyes to identify objects. behind. When the distance between the eyes is still wider than the obstacle - such as fingers, or leaves in the forest - we can look over it. '

To identify this animal with an impressive ability, Changizi studied 319 animals in 17 types of mammals and found that the position of the eye depended on two factors: obstacles, or lack of obstructions. in the environment of animals, and the size of animals compared to obstacles.

Changizi discovered that animals in the environment are not complicated - he describes this environment as ' non-thick space, or where obstacles are larger than the distance between the eyes of the animals' (imagine a little mouse She tried to look through the 6-inch-wide leaves - often with eyes on both sides.

Changizi said: 'Animals that live in a simple, non-thick environment do not have to deal with obstacles regardless of their size or size, so there is no advantage of X-rays or eyes facing them. . The two-eyed look has no benefit to them compared to one-eyed view, they can observe much larger areas with 2 eyes on both sides. '

Photo A: left diagram illustrating the skull of an animal with 2 eyes on both sides.2 half orange circles represent the vision of each eye, and the darker orange triangle represents the area of ​​the eyes visible to the front.The diagram on the right illustrates the area where animals can identify objects in complex environments.Picture B shows the visible area and the eye's eye area with the eye facing forward.( Photo: Rensselaer / Changizi)

However, in a messy environment - Changizi defines a dense space where obstructions are smaller than the distance between the eyes of the animal - the eyes are wider and the eyes are facing forward to can see through obstacles.

Changizi said: 'The ability to see X-rays allows animals with their eyes to move forward to observe the wider area around them compared to the eyes facing the sides. In addition, the larger the animal is in a complex environment, the more their eyes face straight ahead for a broad view, to aid in hunting, fleeing enemies, or moving through dense forests. theater '.

Changizi said the human eye has evolved to be able to look straight, but we live in an environment that is not too complicated, so the eyes on the two sides may be more beneficial for us.

Changi said: 'In today's world, human eyesight is more like a tiny mouse than a large animal in the forest. We don't often see small obstacles, and objects that often block our view - cars and tall buildings - are much wider than the distance between the eyes, so we can't use X-ray power. to look through them. If we freeze and wake up a million years later, it may be very difficult for us to look into the eyes of new residents - because they may have eyes on both sides. '

Changizi's research was completed in collaboration with Shinsuke Shimojo at the California Institute of Technology, and was published online in the Journal of Theoretical Biology.