# The Whites of the Eyes: Why do we have them, but no other critters? **URL:** \ **Category:** Factual Questions\ **Created:** [April 30, 2013, 4:17am UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075 "2013-04-30T04:17:09Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [April 30, 2013, 5:08pm UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/21 "2013-04-30T17:08:27Z")
[Animals with sclera](https://www.google.com/search?q=sclera&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=8Pl_Ub_nLIa0yQHmlYHQDA&biw=1084&bih=1006&sei=-fl_UfTWAoG3ygGl5YDoDA#um=1&client=firefox-a&rls=org.mozilla:en-US%3Aofficial&hl=en&tbm=isch&sa=1&q=animal+sclera&oq=animal+sclera&gs_l=img.3..0.12596.14034.0.14607.7.7.0.0.0.0.152.674.5j2.7.0...0.0...1c.1.11.img.9qAnQshk-9A&bav=on.2,or.r_qf.&bvm=bv.45645796,d.aWc&fp=2c64f6ac7e13f734&biw=1084&bih=1006). ---
**Author:** ![Archaic\_Entity](https://avatars.discourse-cdn.com/v4/letter/a/41988e/32.png) [@Archaic\_Entity](https://boards.straightdope.com/u/Archaic_Entity)\ **Post date:** [April 30, 2013, 5:12pm UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/22 "2013-04-30T17:12:47Z")
> [@panache45](#): > > [Animals with sclera](https://www.google.com/search?q=sclera&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=8Pl_Ub_nLIa0yQHmlYHQDA&biw=1084&bih=1006&sei=-fl_UfTWAoG3ygGl5YDoDA#um=1&client=firefox-a&rls=org.mozilla:en-US%3Aofficial&hl=en&tbm=isch&sa=1&q=animal+sclera&oq=animal+sclera&gs_l=img.3..0.12596.14034.0.14607.7.7.0.0.0.0.152.674.5j2.7.0...0.0...1c.1.11.img.9qAnQshk-9A&bav=on.2,or.r_qf.&bvm=bv.45645796,d.aWc&fp=2c64f6ac7e13f734&biw=1084&bih=1006). I don’t think anyone is arguing that they don’t exist. It’s just a question as to why they’re prominent in humanity, and not other animals. ---
**Author:** ![Teuton](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/teuton/32/3864_2.png) [@Teuton](https://boards.straightdope.com/u/Teuton)\ **Post date:** [April 30, 2013, 5:44pm UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/23 "2013-04-30T17:44:12Z")
> [@panache45](#): > > [Animals with sclera](https://www.google.com/search?q=sclera&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=8Pl_Ub_nLIa0yQHmlYHQDA&biw=1084&bih=1006&sei=-fl_UfTWAoG3ygGl5YDoDA#um=1&client=firefox-a&rls=org.mozilla:en-US%3Aofficial&hl=en&tbm=isch&sa=1&q=animal+sclera&oq=animal+sclera&gs_l=img.3..0.12596.14034.0.14607.7.7.0.0.0.0.152.674.5j2.7.0...0.0...1c.1.11.img.9qAnQshk-9A&bav=on.2,or.r_qf.&bvm=bv.45645796,d.aWc&fp=2c64f6ac7e13f734&biw=1084&bih=1006). That is the most horrible image list I think I have ever seen. Eww. Anyway, one thing it shows is that there actually aren’t many animals with sclera showing - most of the ones that are showing are because a human is holding their eyes open. Most of the exceptions seem to be dogs. ---
**Author:** ![AGuy](https://avatars.discourse-cdn.com/v4/letter/a/bb73d2/32.png) [@AGuy](https://boards.straightdope.com/u/AGuy)\ **Post date:** [April 30, 2013, 7:32pm UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/24 "2013-04-30T19:32:06Z")
I think a lot of people forget (or don’t get) how natural selection works. Traits get selected for if they: 1) help you survive; or 2) Help you produce more viable offspring. Some traits just get lucky and spread because they occur in conjunction with actually useful traits, or because their bearers are aided by circumstances. I can’t imagine more visible sclera having made the difference between life and death in our ancestors. Sexual selection might make sense – perhaps it was considered an attractive trait. Or maybe it had something to do with our increasing brain size, which changed the proportions of our skulls, showing more of the whites of our eyes as a side-effect. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [April 30, 2013, 8:39pm UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/25 "2013-04-30T20:39:31Z")
There was a good thread on why are eyes/pupils round or not, and if not, in which orientation the oval/slit is. i have no time now, but do a search keywords goat (pupil OR oval OR iris). Also, if you or someone finds it, could you post it? ---
**Author:** ![Johanna](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johanna/32/8318_2.png) [@Johanna](https://boards.straightdope.com/u/Johanna)\ **Post date:** [April 30, 2013, 9:41pm UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/26 "2013-04-30T21:41:08Z")
Horses roll their eyes to show the sclera to express anger or fear. ---
**Author:** ![thicksantorum](https://avatars.discourse-cdn.com/v4/letter/t/65b543/32.png) [@thicksantorum](https://boards.straightdope.com/u/thicksantorum)\ **Post date:** [April 30, 2013, 10:52pm UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/27 "2013-04-30T22:52:10Z")
> [@AaronX](#): > > Yes, a good question is are our eyes bigger, or animals’ irises bigger? How about pupil/iris size? > > Maybe animals have bigger pupils, and hence bigger irises because they need to see better at night? > Maybe animals have bigger irises for a wider range of pupil sizes? > Maybe humans just have bigger eyes due to neoteny? It’s mostly how wide the eyes open, not the actual size. Note how humans have relatively over-developed muscles around the eyes that serve to widen the range of facial expressions available, while most other animals can only open and close them. We also have tiny, mostly useless ear muscles, while other species have much more developed ones, used both for rotating their ears and for expressing emotion. ---
**Author:** ![robardin](https://avatars.discourse-cdn.com/v4/letter/r/43a26b/32.png) [@robardin](https://boards.straightdope.com/u/robardin)\ **Post date:** [April 30, 2013, 11:41pm UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/28 "2013-04-30T23:41:17Z")
> [@AGuy](#): > > I can’t imagine more visible sclera having made the difference between life and death in our ancestors. Really? Cuing off of another person’s eyes while otherwise motionless as an indication of interest seems like a very advantageous means of silent communication in a group hunting situation. ---
**Author:** ![AGuy](https://avatars.discourse-cdn.com/v4/letter/a/bb73d2/32.png) [@AGuy](https://boards.straightdope.com/u/AGuy)\ **Post date:** [May 1, 2013, 12:05am UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/29 "2013-05-01T00:05:56Z")
> [@robardin](#): > > Really? Cuing off of another person’s eyes while otherwise motionless as an indication of interest seems like a very advantageous means of silent communication in a group hunting situation. So the people who had small sclera and their families starved to death because they couldn’t hunt? Their companions couldn’t have figured out what to do if they couldn’t see the whites of one of the hunters’ eyes? Somehow wolves and lions, etc. manage to be pretty good group hunters despite their eyes. Sorry, I just don’t see it making much of a difference that way. There are hand signals, calls, and just looking at the iris or head direction, all of which you could use as cues instead. ---
**Author:** ![thicksantorum](https://avatars.discourse-cdn.com/v4/letter/t/65b543/32.png) [@thicksantorum](https://boards.straightdope.com/u/thicksantorum)\ **Post date:** [May 1, 2013, 12:37am UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/30 "2013-05-01T00:37:53Z")
> [@AGuy](#): > > So the people who had small sclera and their families starved to death because they couldn’t hunt? Their companions couldn’t have figured out what to do if they couldn’t see the whites of one of the hunters’ eyes? Somehow wolves and lions, etc. manage to be pretty good group hunters despite their eyes. > > Sorry, I just don’t see it making much of a difference that way. There are hand signals, calls, and just looking at the iris or head direction, all of which you could use as cues instead. You have an overly-simplistic view of how natural selection works. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [May 1, 2013, 1:08am UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/31 "2013-05-01T01:08:59Z")
> [@AGuy](#): > > I can’t imagine more visible sclera having made the difference between life and death in our ancestors. Evolution is about successful breeding, not life and death. And I imagine there’s all sorts of situations where silently indicating with your eyes where something is or that you are interested in something is useful. A woman smiling at a man while looking at him for example; she’s communicating that she’s interested in him, personally, and not the three other guys he’s standing next to. Or if I hold something up and the person I’m talking to glances at it, they don’t need to waste time saying they’ve seen it. Humans are a very communicative species, and this helps that communication work more smoothly. > [@Mijin](#): > > Slight hijack but… > Does anyone know a good list of anatomical features either outright unique to Homo sapiens, or rare outside of the homo genus? Humans [sweat](http://en.wikipedia.org/wiki/Sweat_gland) much more than most other species I understand. We have more [eccrine sweat glands](http://en.wikipedia.org/wiki/Eccrine_sweat_glands) than most. ---
**Author:** ![Civil\_Guy](https://avatars.discourse-cdn.com/v4/letter/c/d78d45/32.png) [@Civil\_Guy](https://boards.straightdope.com/u/Civil_Guy)\ **Post date:** [May 1, 2013, 3:51am UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/32 "2013-05-01T03:51:55Z")
…relative hairlessness (for a non-aquatic mammal, at least), bi-pedal gait, the famous opposable thumbs, continuous female availability for sex (anatomically, that is),… ---
**Author:** ![AGuy](https://avatars.discourse-cdn.com/v4/letter/a/bb73d2/32.png) [@AGuy](https://boards.straightdope.com/u/AGuy)\ **Post date:** [May 1, 2013, 4:26am UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/33 "2013-05-01T04:26:38Z")
> [@thicksantorum](#): > > You have an overly-simplistic view of how natural selection works. That was enlightening, thank you. ---
**Author:** ![AGuy](https://avatars.discourse-cdn.com/v4/letter/a/bb73d2/32.png) [@AGuy](https://boards.straightdope.com/u/AGuy)\ **Post date:** [May 1, 2013, 4:28am UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/34 "2013-05-01T04:28:03Z")
> [@Der\_Trihs](#): > > Evolution is about successful breeding, not life and death. And I imagine there’s all sorts of situations where silently indicating with your eyes where something is or that you are interested in something is useful. A woman smiling at a man while looking at him for example; she’s communicating that she’s interested in him, personally, and not the three other guys he’s standing next to. Or if I hold something up and the person I’m talking to glances at it, they don’t need to waste time saying they’ve seen it. Humans are a very communicative species, and this helps that communication work more smoothly. > > Humans [sweat](http://en.wikipedia.org/wiki/Sweat_gland) much more than most other species I understand. We have more [eccrine sweat glands](http://en.wikipedia.org/wiki/Eccrine_sweat_glands) than most. Yeah, that was my point in post #24 – sexual selection makes more sense as the explanation. ---
**Author:** ![Ulfreida](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ulfreida/32/8014_2.png) [@Ulfreida](https://boards.straightdope.com/u/Ulfreida)\ **Post date:** [May 1, 2013, 4:34am UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/35 "2013-05-01T04:34:52Z")
I thought the sweating thing was an advantage in long-distance running (“persistence hunting”), at which we apparently are the best on the planet. ---
**Author:** ![dougie\_monty](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@dougie\_monty](https://boards.straightdope.com/u/dougie_monty)\ **Post date:** [May 1, 2013, 5:49am UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/36 "2013-05-01T05:49:02Z")
Col. Prescott: “Don’t fire until you see the whites of their eyes!” Soldier: “When _we_ can see the whites of\* their _eyes,_ they \*can see the whites of _our_ eyes! Or hadn’t you _thought_ of that?” What if the Redcoats at Bunker Hill had been suffering from pinkeye? 😃 ---
**Author:** ![thicksantorum](https://avatars.discourse-cdn.com/v4/letter/t/65b543/32.png) [@thicksantorum](https://boards.straightdope.com/u/thicksantorum)\ **Post date:** [May 1, 2013, 5:58am UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/37 "2013-05-01T05:58:24Z")
> [@Ulfreida](#): > > I thought the sweating thing was an advantage in long-distance running (“persistence hunting”), at which we apparently are the best on the planet. It is. Also, running on 2 legs is more energy-efficient than on 4. ---
**Author:** ![Inigo\_Montoya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inigo_montoya/32/124_2.png) [@Inigo\_Montoya](https://boards.straightdope.com/u/Inigo_Montoya)\ **Post date:** [May 1, 2013, 3:21pm UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/38 "2013-05-01T15:21:44Z")
Humans have highly visible sclera because humans without highly visible sclera look really damn creepy and are unlikely to find anyone willing to mate with them. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [May 1, 2013, 7:59pm UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/39 "2013-05-01T19:59:08Z")
> [@thicksantorum](#): > > We also have tiny, mostly useless ear muscles, while other species have much more developed ones, used both for rotating their ears and for expressing emotion. Which is an interesting point. If you have ever had a pet cat, you can read a fair bit from them by looking at their ears, which would serve exactly the same purpose in hunting as reading eye movements. ---
**Author:** ![BMax](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bmax/32/4267_2.png) [@BMax](https://boards.straightdope.com/u/BMax)\ **Post date:** [May 1, 2013, 8:40pm UTC](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075/40 "2013-05-01T20:40:41Z")
While man’s best friend sometimes has a [visible](https://www.google.com/search?q=sclera&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=8Pl_Ub_nLIa0yQHmlYHQDA&biw=1084&bih=1006&sei=-fl_UfTWAoG3ygGl5YDoDA#um=1&newwindow=1&safe=off&client=firefox-a&rls=org.mozilla:en-US%3Aofficial&hl=en&tbm=isch&sa=1&q=dog+sclera&oq=dog+sclera&gs_l=img.3..0i24l6.6248.7737.2.8886.4.4.0.0.0.0.78.309.4.4.0...0.0...1c.1.11.img.wuSCrOqbraE&bav=on.2,or.r_cp.r_qf.&fp=8d0beefa1296a2f7&biw=1366&bih=635)sclera, our closest relative [http://media4.s-nbcnews.com/j/msnbc/Components/Photos/061108/061108\_chimphuman\_hlg\_2p.grid-6x2.jpg](http://media4.s-nbcnews.com/j/msnbc/Components/Photos/061108/061108_chimphuman_hlg_2p.grid-6x2.jpg). Isn’t the major genetic difference between human a chimp the fusion of chromosomes? [Chromosome fusion](http://www.evolutionpages.com/chromosome_2.htm) Could this trait have been caused by the chromosome fusion and later been selected sexually? [Previous page](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075.md?page=1) [Next page](https://boards.straightdope.com/t/the-whites-of-the-eyes-why-do-we-have-them-but-no-other-critters/657075.md?page=3)