You may have noticed that predator animals tend to have their eyes on the front of their skulls (like us), while prey animals (like sheep and rabbits) have their eyes on the sides. The ones we need are things like depth perception, the ability to see movement, and color vision. Depending on what the animal does to survive, that requires different adaptations. One thing all eyes have in common is that they focus light onto a retina, turn the image into signals, and send them to the brain. There are some incredible eyes in nature that work very differently from the way human eyes do. However, every once in a while, we like taking a look at the fascinating world of animal eyesight. Our jobs are all about keeping human eyes healthy and making sure our patients see clearly. 'When you hold up your finger vertically and fixate your eyes on something far beyond it,' he writes, 'you perceive two copies of your finger, and both copies of your finger appear transparent.' Thus, you have the ability to 'see through' your finger, as though you were seeing with X-ray vision.Differences Between Human and Animal Eyes The catchy name for his hypothesis comes from a curious phenomenon. In short, forward-facing eyes allowed our ancestors to see through the dense leaves and branches in their forest habitat. In 2008 in the Journal of Theoretical Biology, he offered up the 'X-ray vision hypothesis'. Theoretical neurobiologist Mark Changizi has yet another idea. As it happens, early primates were also nocturnal hunters, and their adaptation for nighttime predation may have granted forward-facing eyes to all their descendants, including our own species. Allman's contribution was to suggest that forward-facing eyes proved beneficial for creatures that hunt at night, such as owls and cats, because they can take in more light than sideways-facing eyes.

Cats, primates and owls do, but not mongooses, tree shrews, and robins. Not all predators, after all, have forward facing eyes. Neurobiologist John Allman picked up on Cartmill's hypothesis and expanded it to focus on nocturnal predation. Cartmill thought that the reduction in their ability to smell was a side effect of the eyes' convergence, simply because the space available for the nose and its connections to the brain became smaller as it was crowded out by the eyes. Early primates, for example, hunt by sight rather than by scent. Cartmill thought his explanation was the most elegant, because it also explained other evolutionary changes that are distinctive to primates. That would help them to better locate and more effectively take down their prey, whether that's a leopard stalking a gazelle or a raptor snatching a rabbit in its talons, or one of our primate ancestors grabbing an insect from the branch of a tree. Predators are best served, ostensibly, by having extremely good depth perception. So, in 2005, biological anthropologist Matt Cartmill proposed a different idea: the 'visual predation hypothesis'. The problem with Collins’ hypothesis is that many animals that thrive in trees have eyes on the sides of their heads – squirrels, for instance. “The price of failure was to drop many metres onto a ground inhabited by carnivorous beasts,' wrote visual psychotherapist Christopher Tyler in 1991. After all, the stakes for failing to work out the true distance between trees were high. In the decades since, it has been expanded and refined, but the basic idea that our ancestors evolved forward facing eyes to accurately judge distances while leaping from tree to tree remained central for quite a while. Collins' idea has become known as the 'arboreal locomotion hypothesis' – arboreal meaning living in trees.

Predator eyes vs prey eyes human