“The left and right eyes see the same object from different angles; the images formed on the retina are not entirely identical. After the brain combines these two images, it can distinguish front from back, near from far, thereby producing stereoscopic vision.” — Baidu Encyclopedia (on stereoscopic film)

I watched an episode of Discovery about the differences in stereoscopic vision among animals. The angular difference between what the two eyes see is the stereoscopic field of view; biologically, a wider stereoscopic field means a faster ability to judge and locate moving objects in space. Large cats, for instance, all have a wide stereoscopic field, allowing them to react quickly to prey movement. Herbivores, by contrast, tend to have a narrower stereoscopic field, because when a predator comes, they usually only need to bolt in one direction, so they don’t need too wide a field. Look closely, and you’ll see that the eyes of predators differ from those of ordinary (hunted) animals. Nothing about how things develop is accidental. Nature is cruel — it forces living things to evolve, and only those who manage to squeeze through the cracks earn the right to keep living.