# How does evolution make the eye? **URL:** \ **Category:** Factual Questions\ **Created:** [August 3, 2018, 4:47pm UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050 "2018-08-03T16:47:45Z")\ **Posts on this page:** 17\ **Page:** 2
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [August 3, 2018, 8:02pm UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050/21 "2018-08-03T20:02:18Z")
I don’t see anything magical about the eye… As others point out - start with alight-sensitive spot. A lot of evolution consists of accidental doubling and re-doubling of genetic instructions. We still get the occasional sixth finger or sixth toe instance… Crustacea like lobsters, or even insects, are a great example. Start with a simple organism, double up, double up again, to get multiple segments - eventually specific segments evolve specialized limbs for specific tasks. So one light sensitive spot becomes two or more… If they are in an indent, then this assists in determining directionality - another advantage. When I was particularly badly sunburned (or stove-burned) I got blisters, which were water-filled blobs under my surface layer of skin. It’s not hard to imagine this as a logical evolution of “how does the body protect the critical light-sensitive spots?” The organisms whose eye coverings best shape like the appropriate lens have sharper vision, a survival attribute. the ability to move the top of this light-sensitive pit gives a bit more precision to the evolving vision. So just as you can wiggle your nose or ears, or smile, the muscles that can move the “eyehole” can significantly improve ability to quickly change direction of view, without moving the whole body. Some more primitive animals have eyes on stalks, but a critical survival capacity means the eye should be less vulnerable, should not stick out. So an eyehole that can be moved internally gives an advantage; so imagine an animal can point the eye pit sort of like how you can wiggle your nose to point your nostrils slightly one way or the other. Or… move your tongue inside your mouth to point where you want… And of course, evolution likes to take a good idea and run with it. Eventually an aimable pit lined with light sensitive nerves becomes a more rounded ball-like structure with far greater ability to aim. more than one light-sensitive spot becomes tens of thousands. And of course, the neural networks in the brain that interpret the images have evolved with the quality of the eyes… from simple “am I in the light or hidden?” to recognizing familiar shapes and analyzing what is seen. There are dozens of other “design” decisions that evolution has made. The closer the eyes are to the brain, the shorter the nerve connection, the less likely an accident will cause blindness; if your eyes were in your fingers, any bad accident could damage them and make you blind, a severe evolutionary disadvantage. It’s a lot easier to get by with a few fingers missing than to go blind. Eye placement evolves according to need - horses or chickens that need to see enemies coming in any direction have eyes that cover 360 degrees; animals that jump form tree to tree or onto their prey have better advantages with depth perception provided by side-by-side eyes… and so on. ---
**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:** [August 3, 2018, 8:54pm UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050/22 "2018-08-03T20:54:36Z")
> [@Leo\_Bloom](#): > > …even there today you have complete eyeballs underneath a semi-transparent skin in some fishes. > > Neat cite/photo of one spooky looking fish to come… > > > [@Leo\_Bloom](#): > > > > [Ta-daah!](https://www.mbari.org/barreleye-fish-with-tubular-eyes-and-transparent-head/) > > > > > [@Atamasama](#): > > > > > > Thanks for that Leo. That fish was less “spooky” than simply “awesome”. You made my day with that. What makes weirder in trying to get your head around this fish (as it were) is that what you think are its eyes are its nostrils. Sort of like [this](http://images.realclear.com/368441_5_.jpg). ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [August 3, 2018, 9:27pm UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050/23 "2018-08-03T21:27:57Z")
I seem to recall that the light sensitive spots evolved into eyes in animals but into chloroplasts (the photosynthetic organelles) in plants. Evolution works in wondrous ways. Amazingly the eye has apparently evolved about 40 times in different groups of animals. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [August 3, 2018, 10:18pm UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050/24 "2018-08-03T22:18:33Z")
Something about that fish seemed familiar; then I remembered this picture from _Codex Seraphinianus_. [![](http://greenwoodsoftware.com/misc/codex1.jpg) ](http://greenwoodsoftware.com/misc/codex1.jpg) ---
**Author:** ![drad\_dog](https://avatars.discourse-cdn.com/v4/letter/d/aeb1de/32.png) [@drad\_dog](https://boards.straightdope.com/u/drad_dog)\ **Post date:** [August 3, 2018, 11:20pm UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050/25 "2018-08-03T23:20:58Z")
Great stuff. I’m glad I didn’t just wiki it. If eyes developed at different times independently that’s indicative of a logic to it. I’m trying to get past how long there had to be things without eyes before there were. Imagine waiting for evolution to happen? And it does and someone else wants to watch the price is right or something. ---
**Author:** ![Lord\_Mondegreen](https://avatars.discourse-cdn.com/v4/letter/l/91b2a8/32.png) [@Lord\_Mondegreen](https://boards.straightdope.com/u/Lord_Mondegreen)\ **Post date:** [August 3, 2018, 11:24pm UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050/26 "2018-08-03T23:24:48Z")
> [@jayjay](#): > > And was Richard Dawkins wife until 2016. (And was Tom Baker’s (Doctor Who) wife for a while before that.) Lalla and Richard were introduced to each other by Douglas Adams at his (Douglas’s) 40th birthday party. [/sidetrack] ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [August 4, 2018, 12:02am UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050/27 "2018-08-04T00:02:25Z")
> [@TriPolar](#): > > I think that sleep is somehow tied to the development of eyes since they would have been useless at night. Only human eyes. Many animals are nocturnal, and their eyes are adapted to see very well at night (compared to humans). Some examples: many birds, like owls, hunters like foxes & raccoons, cats, some dogs (though they use smell even more), horses, etc. You can often recognize these animals because their eyes are big (compared to their size) and because their eyes seem to glitter in the dark (due to a reflecting layer in their eyes). ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [August 4, 2018, 12:04am UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050/28 "2018-08-04T00:04:56Z")
Plus even worms sleep > **[Analyzing a Worm's Sleep](https://www.caltech.edu/about/news/analyzing-worms-sleep-51729)** > > New research from Caltech finds three chemicals that collectively work together to induce sleep in the roundworm C. elegans. ---
**Author:** ![nelliebly](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nelliebly/32/5422_2.png) [@nelliebly](https://boards.straightdope.com/u/nelliebly)\ **Post date:** [August 4, 2018, 12:09am UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050/29 "2018-08-04T00:09:07Z")
> [@Leo\_Bloom](#): > > [Ta-daah!](https://www.mbari.org/barreleye-fish-with-tubular-eyes-and-transparent-head/) Mind. Boggled. So cool! ---
**Author:** ![jasg](https://avatars.discourse-cdn.com/v4/letter/j/f0a364/32.png) [@jasg](https://boards.straightdope.com/u/jasg)\ **Post date:** [August 4, 2018, 12:12am UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050/30 "2018-08-04T00:12:39Z")
This question reminds me of a book from some years back - [Life’s Solution](https://www.nytimes.com/2003/11/30/books/it-had-to-happen.html) by Simon Conway Morris. In it, he points out : > [@](#): > > The camera eye found in vertebrates has independently evolved in other groups – in squid, some marine worms, jellyfish, snails and spiders. In addition to such standard examples of convergence (like the remarkable similarities that unite placental and marsupial mammals), Conway Morris presents scores of fascinating examples that are less familiar. The lesson is clear. The living world is peppered with recurrent themes; it is not an accumulation of unique events. As I recall, he shows that the vertebrate and cephalopod eyes are anatomically similar but derive from very different embryonic tissues. As noted above the eye has evolved independently many times. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [August 4, 2018, 12:14am UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050/31 "2018-08-04T00:14:16Z")
> [@Tim\_T-Bonham.net](#): > > Only human eyes. > Many animals are nocturnal, and their eyes are adapted to see very well at night (compared to humans). Some examples: many birds, like owls, hunters like foxes & raccoons, cats, some dogs (though they use smell even more), horses, etc. > > You can often recognize these animals because their eyes are big (compared to their size) and because their eyes seem to glitter in the dark (due to a reflecting layer in their eyes). I’m talking about the early development of eyes and sleep. And nocturnal animals still sleep. ---
**Author:** ![nelliebly](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nelliebly/32/5422_2.png) [@nelliebly](https://boards.straightdope.com/u/nelliebly)\ **Post date:** [August 4, 2018, 12:32am UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050/32 "2018-08-04T00:32:49Z")
I certainly understand how photosensitive cells give an evolutionary advantage, but what kind of cells did those cells evolve from? Ironically, it’s having experiencied sequentially the differences that corneal disease (and donor corneas), glaucoma, and macular damage from a lupus med have made to my vision that’s helped me understand the functions of the various parts and mechanisms of the eye better than I could have if I were still fully sighted or had been born blind. Pretty freaking incredible. I hope _not_ to understand the complex functioning of other organs the same way. 🙂 ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [August 4, 2018, 12:41am UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050/33 "2018-08-04T00:41:09Z")
> [@nelliebly](#): > > I certainly understand how photosensitive cells give an evolutionary advantage, but what kind of cells did those cells evolve from? > > Ironically, it’s having experiencied sequentially the differences that corneal disease (and donor corneas), glaucoma, and macular damage from a lupus med have made to my vision that’s helped me understand the functions of the various parts and mechanisms of the eye better than I could have if I were still fully sighted or had been born blind. Pretty freaking incredible. > > I hope _not_ to understand the complex functioning of other organs the same way. 🙂 Depends who’s eye you are talking about, for us humans they came from Cilia and in other lines from Flagella. > **[Cilia and Flagella - Difference and Comparison | Diffen](https://www.diffen.com/difference/Cilia_vs_Flagella)** > > Cilia and flagella are cell organelles that are structurally similar but are differentiated based on their function and/or length. Cilia are short and there are usually many (hundreds) cilia per cell. On the other hand, flagella are longer and there... ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [August 4, 2018, 3:33am UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050/34 "2018-08-04T03:33:51Z")
[Interesting (if long and highly technical) page on the origin of opsins](http://genomewiki.ucsc.edu/index.php/Opsin_evolution:_orgins_of_opsins). ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [August 4, 2018, 8:22am UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050/35 "2018-08-04T08:22:52Z")
> [@jasg](#): > > As noted above the eye has evolved independently many times. I’m fairly sure Conway Morris is wrong. Eyes have evolved into very different types and in different tissues, but they have a monophyletic origin, since they all share the **pax6** gene and use the same chemistry. The origin of light-sensitive organs goes back a lot further than Conway Morris seems to think. But I think he is wrong about a lot of things. ---
**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:** [August 4, 2018, 1:04pm UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050/36 "2018-08-04T13:04:10Z")
> [@Tim\_T-Bonham.net](#): > > Only human eyes. > Many animals are nocturnal, and their eyes are adapted to see very well at night (compared to humans)… This might’ve gotten lost in the thread, but before eyes and with just a bunch of photosensitive molecules, the whole point (well, a whole point) was that organisms could see that night and day actually was a thing, and to thrive upon that. ---
**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:** [August 4, 2018, 10:15pm UTC](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050/37 "2018-08-04T22:15:03Z")
For all those in this thread (and elsewhere) I cannot recommend highly enough the endlessly fascinating and beautifully diagrammed and illustrated book **[Animal Eyes](https://www.amazon.com/Animal-Eyes-Oxford-Biology/dp/0198509685)**, by Land and Nilsson. [Previous page](https://boards.straightdope.com/t/how-does-evolution-make-the-eye/819050.md?page=1)