Is there anything solid known about eye position (front vs. side of skull) and other aspects of an organism’s life? It seems to me that front of the skull correlates with being a hunter, but (as is usual with biology) there may well be exceptions.
Probably worth noting that fish, even predatory ones, don’t necessarily have binocular vision, and vice versa for herbivores. Sperm whales are the largest living predators and lack it; fruit bats, who don’t hunt, do have it.
There ARE incentives to develop it, or retain it, based on those lifestyle differences, but it makes for a somewhat fuzzy heuristic.
The other thing is this is pretty much restricted to fish and their mutant descendants, the tetrapods. Get outside the chordates and you find different solutions to these problems. Arthropods have several distinct kinds of eye architecture and sometimes their strategies generalize well: house flies (which are prey and scavengers) and dragonflies (which hunt) both have similarly-structure eyes; if anything I think the dragonfly has wider coverage. Spiders often rely on widely-placed eyes of differing strengths and ranges; mantis shrimp only have the two eyes, on stalks, and are renowned predators.
So it might look like a generalizable rule because it applies to so many of the most obvious, easy-to-examine large animals you can find, but remember they’re our close anatomical cousins, and they’re solving the problem with very similar design constraints.
(Also, primates—many primates who spend a lot of time in trees, but don’t hunt, have binocular vision. In their case it’s there because of its benefits for rangefinding and spacial awareness in an arboreal environment.)
I have read stuff that posited that hunters have front eyes (I think the reason given was for more accurate depth perception), and that prey-animals have eyes towards the side of their head to give a wider field of vision.
Some animals, usually but not always prey animals, have their two eyes positioned on opposite sides of their heads to give the widest possible field of view. Examples include rabbits, buffaloes, and antelopes. In such animals, the eyes often move independently to increase the field of view. Even without moving their eyes, some birds have a 360-degree field of view.
Other animals, usually but not always predatory animals, have their two eyes positioned on the front of their heads, thereby allowing for binocular vision and reducing their field of view in favor of stereopsis. Examples include humans, eagles, wolves, and snakes.
Some predator animals, particularly large ones such as sperm whales and killer whales, have their two eyes positioned on opposite sides of their heads. Other animals that are not necessarily predators, such as fruit bats and a number of primates also have forward facing eyes. These are usually animals that need fine depth discrimination/perception; for instance, binocular vision improves the ability to pick a chosen fruit or to find and grasp a particular branch.
I was wondering whether the rules might be different for sea creatures because of hydrodynamics. Practically all fish have their eyes on the sides of their heads. It’s possible that understanding hammerhead sharks and flounders would be too hard.
Puffer fish are fish which have eyes at or near the front of their heads, but they aren’t built for chasing things down. I just found out that you can get a puffer fish to chase a laser. I don’t know what that proves. Maybe they chase relatively small slow prey.
Puffers are sometimes pelagic (ocean-going) for parts of their life cycle, but typically they hang out in reefs, brackish areas, or other near-shore zones and hunt smallish prey, “sprinting” it down and delivering a quick snap, or just teasing it out from hiding places among coral or plants. They use the same “sprint” to evade attack.
Puffers also have the ability to swivel their eyes independently, like a chameleon.
I think that the rules are different for sea creatures simply because accurate sight is usually a less useful position sense in water. In most places you can’t see far away no matter how good your eyes are, so just noticing shadows is mostly enough. Sound (including vibrations and currents) tends to be more useful there, hence echolocation and the lateral line, as is smell (see sharks). Basically, you can’t hunt much with sight, but it’s still useful to avoid being hunted.
There are some exceptions, like octopi (big eyes) and some fish with curiously complex sight (poly-chromatic, polarization-sensitive eyes) I don’t have a very good explanation for. But I’d guess they’re a bit like bats for land animals, some accident of evolution probably threw them on a tangent and they found a “local maxima” of fitness.
Is there anything solid known about eye position (front vs. side of skull) and other aspects of an organism’s life? It seems to me that front of the skull correlates with being a hunter, but (as is usual with biology) there may well be exceptions.
For example, lemurs aren’t especially hunters, but they have eyes in front.
I was thinking that cats are both hunters and prey, and they have eyes in front.
Also, what about the evolution of eye position? How much of a lag is there if living conditions change?
Probably worth noting that fish, even predatory ones, don’t necessarily have binocular vision, and vice versa for herbivores. Sperm whales are the largest living predators and lack it; fruit bats, who don’t hunt, do have it.
There ARE incentives to develop it, or retain it, based on those lifestyle differences, but it makes for a somewhat fuzzy heuristic.
The other thing is this is pretty much restricted to fish and their mutant descendants, the tetrapods. Get outside the chordates and you find different solutions to these problems. Arthropods have several distinct kinds of eye architecture and sometimes their strategies generalize well: house flies (which are prey and scavengers) and dragonflies (which hunt) both have similarly-structure eyes; if anything I think the dragonfly has wider coverage. Spiders often rely on widely-placed eyes of differing strengths and ranges; mantis shrimp only have the two eyes, on stalks, and are renowned predators.
So it might look like a generalizable rule because it applies to so many of the most obvious, easy-to-examine large animals you can find, but remember they’re our close anatomical cousins, and they’re solving the problem with very similar design constraints.
(Also, primates—many primates who spend a lot of time in trees, but don’t hunt, have binocular vision. In their case it’s there because of its benefits for rangefinding and spacial awareness in an arboreal environment.)
I have read stuff that posited that hunters have front eyes (I think the reason given was for more accurate depth perception), and that prey-animals have eyes towards the side of their head to give a wider field of vision.
I’ll see if I can refind any of that stuff.
I didn’t find exactly what I was thinking of (I think it was probably a book), but a section of the Binocular vision wikipedia article has some information (uncited, unfortunately). Specifically:
I was wondering whether the rules might be different for sea creatures because of hydrodynamics. Practically all fish have their eyes on the sides of their heads. It’s possible that understanding hammerhead sharks and flounders would be too hard.
Puffer fish are fish which have eyes at or near the front of their heads, but they aren’t built for chasing things down. I just found out that you can get a puffer fish to chase a laser. I don’t know what that proves. Maybe they chase relatively small slow prey.
Puffers are sometimes pelagic (ocean-going) for parts of their life cycle, but typically they hang out in reefs, brackish areas, or other near-shore zones and hunt smallish prey, “sprinting” it down and delivering a quick snap, or just teasing it out from hiding places among coral or plants. They use the same “sprint” to evade attack.
Puffers also have the ability to swivel their eyes independently, like a chameleon.
I think that the rules are different for sea creatures simply because accurate sight is usually a less useful position sense in water. In most places you can’t see far away no matter how good your eyes are, so just noticing shadows is mostly enough. Sound (including vibrations and currents) tends to be more useful there, hence echolocation and the lateral line, as is smell (see sharks). Basically, you can’t hunt much with sight, but it’s still useful to avoid being hunted.
There are some exceptions, like octopi (big eyes) and some fish with curiously complex sight (poly-chromatic, polarization-sensitive eyes) I don’t have a very good explanation for. But I’d guess they’re a bit like bats for land animals, some accident of evolution probably threw them on a tangent and they found a “local maxima” of fitness.