Humans share with other primates the ability to see in depth, in three dimensions. This kind of depth perception is made possible by the positioning of our eyes in the front of our heads. Our brains are capable of processing the slight differences between what the left and right eyes see, and we perceive these differences as spatial depth. This ability would be necessary to animals that lived in trees and apparently evolved with that mode of life.  Herbivores, like horses, often have their eyes positioned on the sides of their heads, and that means their eyes are not adapted for stereoscopic vision, but for catching a glimpse of a predator approaching from behind.

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