dbaupp comments on Open Thread, September 1-15, 2012 - Less Wrong

6 Post author: OpenThreadGuy 01 September 2012 08:13AM

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Comment author: NancyLebovitz 02 September 2012 03:05:30PM 3 points [-]

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?

Comment author: dbaupp 02 September 2012 04:37:55PM *  1 point [-]

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:

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.

Comment author: NancyLebovitz 02 September 2012 09:02:27PM 0 points [-]

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.

Comment author: [deleted] 03 September 2012 06:27:25AM 1 point [-]

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.

Comment author: bogdanb 04 September 2012 10:17:24PM *  0 points [-]

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.

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