Now I’m curious why, as far as I know, no animal has ever evolved an eye in the back of its head. You mention bipedality and descent from trees, but why wouldn’t a gazelle or a fly or a small fish get an advantage from one?
Gazelle can afford to move it’s eyes to sides of the head (not being a predator), the fly has near omni-directional vision.
The predators, however, have a problem—they can’t move the eyes to sides of the head, because that will lose the sharp binocular vision they need to stalk the prey. So it is predatory species that would benefit the most from a rear view eye. The chameleon evolved very peculiar eyes, but that’s the only solution the predatory vertebrates got.
The spookfish evolved rear view mirrors that it uses to look down and up at same time. As well, there is parietal eye, but this one is very ancient and traces all the way back to time when ancestors of those animals were more transparent and it was a straightforward adaptation to add light sensitivity to some cells in the brain.
It is extremely difficult to evolve eye on back of the head. It’s rare dumb luck, it takes a lot of generations, and existing eyes don’t end up duplicated (except in insects and spiders etc which apparently have more flexible coding for eyes; but even in those this kind of thing doesn’t happen overnight).
The point of the example is that it is not enough to show that something is advantageous, to show that it is possible to evolve. Furthermore, thanks for bringing up the gazelles—that serves as an example of how evolution really solves the rear-view problem. It doesn’t create new photosensitive modules, or replicate existing ones. It just moves the eyes to sides of the head. Keep in mind that eyes, developmentally, are modules of the brain.
The evolutionary psychologists don’t take that empirical knowledge of the ways of evolution into account in any way; that’s why i would say they are misusing word ‘evolution’ to mean ‘magic’; the word evolution ought to encompass our knowledge of how evolution works, whereas the magic can do anything.
Prey animals generally have their eyes on the sides of their heads, which do a good job of covering all directions. And eyes are expensive—they need a lot of brain.
The flatfish has one eye that moves to the other side of its head.
Edit: to clarify: two eyes, one of which moves to the other side of its head as it grows. Richard Dawkins is fond of this example, using it in The Blind Watchmaker and The Greatest Show On Earth.
Flies have compound eyes which allow nearly omnidirectional vision. Evolving a new eye when you’ve already got hair in the way is probably hard, since it would get in the way of a simple light sensitive patch as a starting point, and even if a specimen did mutate one it would probably offer a very weak advantage compared in a species that already has fully developed binocular vision and the ability to turn its head.
Now I’m curious why, as far as I know, no animal has ever evolved an eye in the back of its head. You mention bipedality and descent from trees, but why wouldn’t a gazelle or a fly or a small fish get an advantage from one?
Gazelle can afford to move it’s eyes to sides of the head (not being a predator), the fly has near omni-directional vision.
The predators, however, have a problem—they can’t move the eyes to sides of the head, because that will lose the sharp binocular vision they need to stalk the prey. So it is predatory species that would benefit the most from a rear view eye. The chameleon evolved very peculiar eyes, but that’s the only solution the predatory vertebrates got.
The spookfish evolved rear view mirrors that it uses to look down and up at same time. As well, there is parietal eye, but this one is very ancient and traces all the way back to time when ancestors of those animals were more transparent and it was a straightforward adaptation to add light sensitivity to some cells in the brain.
It is extremely difficult to evolve eye on back of the head. It’s rare dumb luck, it takes a lot of generations, and existing eyes don’t end up duplicated (except in insects and spiders etc which apparently have more flexible coding for eyes; but even in those this kind of thing doesn’t happen overnight).
The point of the example is that it is not enough to show that something is advantageous, to show that it is possible to evolve. Furthermore, thanks for bringing up the gazelles—that serves as an example of how evolution really solves the rear-view problem. It doesn’t create new photosensitive modules, or replicate existing ones. It just moves the eyes to sides of the head. Keep in mind that eyes, developmentally, are modules of the brain.
The evolutionary psychologists don’t take that empirical knowledge of the ways of evolution into account in any way; that’s why i would say they are misusing word ‘evolution’ to mean ‘magic’; the word evolution ought to encompass our knowledge of how evolution works, whereas the magic can do anything.
Side thought: dividing the world into predators and prey is an oversimplification. Cats, for example, are both. I’m not sure how common this is.
Prey animals generally have their eyes on the sides of their heads, which do a good job of covering all directions. And eyes are expensive—they need a lot of brain.
The flatfish has one eye that moves to the other side of its head.
Edit: to clarify: two eyes, one of which moves to the other side of its head as it grows. Richard Dawkins is fond of this example, using it in The Blind Watchmaker and The Greatest Show On Earth.
Flies have compound eyes which allow nearly omnidirectional vision. Evolving a new eye when you’ve already got hair in the way is probably hard, since it would get in the way of a simple light sensitive patch as a starting point, and even if a specimen did mutate one it would probably offer a very weak advantage compared in a species that already has fully developed binocular vision and the ability to turn its head.
Some species have developed additional eyes evolving independently from their original sets though