DISCOVER Magazine. Science, Technology and The Future
Current Issue
Subscribe Today »
  • Renew
  • Give a Gift
  • Archives
  • Customer Service
  • Facebook
  • Twitter
  • Newsletter
  • Health & Medicine
  • Mind & Brain
  • Technology
  • Space
  • Human Origins
  • Living World
  • Environment
  • Physics & Math
  • Video
  • Photos
  • Podcast
  • RSS
Not Exactly Rocket Science
« Individual neurons go to sleep while rats stay awake
Why box jellyfish always have four eyes on the sky »

The eyes have it – incredible ways of seeing the world

<p>In the animal kingdom, eyes have evolved dozens of times. We’re familiar with the camera-style eyes in our own heads, and the weird compound eyes of insects, but there are far weirder ones out there. Scientists are discovering new structures and adaptations all the time. There are eyes with mirrors, eyes with optical fibres, and eyes with bifocal lenses. There are eyes that see in the dark, move around heads, or go into sleep mode. <span> </span>There are even eyes made of rock. This slideshow will take you on a tour of some of these recent eye-opening discoveries.</p><p>Eyes don’t even have to be organic. While most animal lenses are made of proteins, the fuzzy chiton – an armoured relative of snails and other molluscs – has <a href="http://blogs.discovermagazine.com/notrocketscience/2011/04/14/chitons-see-with-eyes-made-of-rock/">lenses made of rock</a>. The lenses are made of aragonite, a type of limestone and the same stuff that the chiton’s shell is made of. These rocky eyes give the chiton a view that’s a thousand times fuzzier than ours, but that’s still good enough to see passing predators. The eyes also erode as the chiton ages, which might explain why it has more than a hundred of them. <span> </span></p>
<p><strong>Read more: </strong><a title="Permanent Link: Chitons see with eyes made of rock" href="http://blogs.discovermagazine.com/notrocketscience/2011/04/14/chitons-see-with-eyes-made-of-rock/">Chitons see with eyes made of rock</a></p><p>Benjamin Franklin is credited with inventing bifocal glasses. These allow wearers to focus on both far and near objects by looking through different parts of the lens. But such lenses have been around for millions of years, on the <a href="http://blogs.discovermagazine.com/notrocketscience/2010/08/29/the-beetle-with-bifocal-eyes/">nightmarish face of the sunburst diving beetle</a>. The beetle’s larva has six pairs of eyes, and the front set is unique in the animal kingdom. Each one has one lens and two retinas, one sitting behind and slightly below the other. The lens manages to focus sharp images onto both of them, so the beetle can see near and far objects at the same time, with equal sharpness. Its bifocal lens gives it two eyes for the price of one.</p>
<p><strong>Read more:</strong> <a title="Permanent Link: The beetle with bifocal eyes" href="http://blogs.discovermagazine.com/notrocketscience/2010/08/29/the-beetle-with-bifocal-eyes/">The beetle with bifocal eyes</a></p><p>In the deep ocean, the brownsnout spookfish can look up and down at the same time, with some of the animal kingdom’s strangest eyes. Each one is split into two connected parts, so it looks like the spookfish has four eyes. One half points up and the other points down, allowing the fish to look at both sky and abyss simultaneously. The downward eye is unique. Unlike the eyes of all other back-boned animals, which use a lens to focus light, <a href="http://blogs.discovermagazine.com/notrocketscience/2008/12/30/spookfish-eye-uses-mirrors-instead-of-a-lens/">this one uses mirrors.</a> It uses hundreds of tiny crystals, arranged in a curved shape, to collect and focus light.</p>
<p>By reflecting light, rather than refracting it, these outer eyes could produce brighter images with higher contrasts that lens-carrying eyes normally would. That must give the fish a great advantage in the deep sea, where the ability to spot even the dimmest and briefest of lights can mean the difference between eating and being eaten.</p>
<p><strong>Read more: </strong><a title="Permanent Link: Spookfish eye uses mirrors instead of a lens" href="http://blogs.discovermagazine.com/notrocketscience/2008/12/30/spookfish-eye-uses-mirrors-instead-of-a-lens/">Spookfish eye uses mirrors instead of a lens</a></p><p>The box jellyfish isn’t just a simple blob of goo. It’s an active predator that hunts with 24 eyes. These are clustered into four groups of six. In each cluster, four eyes are simple pits or slits that sense the presence of light. The other two actually see images and they’re remarkably similar to our eyes. They have their own lenses, retinas and corneas, and they’re <a href="http://blogs.discovermagazine.com/notrocketscience/2008/06/16/jellyfish-and-human-eyes-assembled-using-similar-genetic-building-blocks/">even made using very similar genes</a>. Even though we’re separated by millions of years of evolution, box jellyfish and back-boned animals have evolved eyes by independently recruiting the same building blocks.</p>
<p>The eye clusters are weighed down by heavy crystals so they're always upright, even if the jellyfish is swimming upside-down. This gives the animal <a href="http://blogs.discovermagazine.com/notrocketscience/2011/04/28/why-box-jellyfish-always-have-four-eyes-on-the-sky/">a perpetual view of the sky</a>, which allows it to stay close to the mangrove forests where its prey lives.</p>
<p>(<em>Photos by Anders Garm</em>)</p>
<p><strong>Read more: </strong><a title="Permanent Link: Jellyfish and human eyes assembled using similar genetic building blocks" href="http://blogs.discovermagazine.com/notrocketscience/2008/06/16/jellyfish-and-human-eyes-assembled-using-similar-genetic-building-blocks/">Jellyfish and human eyes assembled using similar genetic building blocks</a></p><p>Mantis shrimps have the arguably the most incredible eyes of any animal. Each eye has three areas that can independently focus on objects, which means that a single mantis shrimp eye has “trinocular vision”. Our eyes have receptors that are tuned to three colours; those of mantis shrimps are tuned to at least twelve. And they can tune individual light-sensitive cells to local light levels.</p>
<p>Mantis shrimps can even see a special type of light – ‘circularly polarised light’ – <a href="http://blogs.discovermagazine.com/notrocketscience/2008/03/21/mantis-shrimps-have-a-unique-way-of-seeing" target="_blank">that no other animal can</a>. This ability allows them to send secret messages, produced by circularly polarised light reflecting off different parts of their shell. The ability hinges on a structure in their eyes that’s <a href="http://blogs.discovermagazine.com/notrocketscience/2009/10/25/mantis-shrimp-eyes-outclass-dvd-players-inspire-new-technology/">similar to technology found in our CD and DVD players</a>. The mantis shrimp’s biological engineering completely outclasses our man-made efforts; if we could duplicate it, we could have the basis of tomorrow’s multimedia players and hard drives.</p>
<p><strong>Read more: </strong><a title="Permanent Link: Mantis shrimps have a unique way of seeing" href="http://blogs.discovermagazine.com/notrocketscience/2008/03/21/mantis-shrimps-have-a-unique-way-of-seeing/">Mantis shrimps have a unique way of seeing</a>; <a title="Permanent Link: Mantis shrimp eyes outclass DVD players, inspire new technology" href="http://blogs.discovermagazine.com/notrocketscience/2009/10/25/mantis-shrimp-eyes-outclass-dvd-players-inspire-new-technology/">Mantis shrimp eyes outclass DVD players, inspire new technology</a></p><p>When we go to sleep at night, we close our eyes to stop any errant light from disturbing our slumber. But the larvae of zebrafish go one further. They <a href="http://blogs.discovermagazine.com/notrocketscience/2010/03/09/pocket-science-chameleons-hunt-with-cold-proof-tongues-and-zebrafish-babies-go-blind-at-night/">shut down their eyes entirely at night</a>, becoming temporarily blind. Their vision only returns when daylight does. Energy is precious to the baby fish and eyes are gas-guzzling appliances, even when they’re set to standby. It makes sense to just shut them off instead.</p>
<p><strong>Read more: </strong><a title="Permanent Link: Pocket Science – chameleons hunt with cold-proof tongues and zebrafish babies go blind at night" href="http://blogs.discovermagazine.com/notrocketscience/2010/03/09/pocket-science-chameleons-hunt-with-cold-proof-tongues-and-zebrafish-babies-go-blind-at-night/">Pocket Science –zebrafish babies go blind at night</a></p><p>Even our own familiar eyes have hidden surprises. In 2009, scientists found that we’re all <a href="http://blogs.discovermagazine.com/notrocketscience/2009/02/08/living-optic-fibres-bypass-the-retinas-incompetent-design/">carrying living optic fibres called Muller cells</a>. These cells help to get round a structural problem in our eyes, where the light-sensing cells of the retina lie behind a tangled mass of nerves and blood vessels. It’s a bit like designing a camera, and sticking the wiring in front of the lens. Light gets through the mess inside the long, cylindrical Muller cells. It reflects down the cell, much like in an optic fibre, to hit the light-sensing cells on the other side. (<em>Image by <a href="http://commons.wikimedia.org/wiki/File:Human_left_eye-8.jpg">Elyzhium</a></em>)</p>
<p><strong>Read more: </strong><a title="Permanent Link: Living optic fibres bypass the retina’s incompetent design" href="http://blogs.discovermagazine.com/notrocketscience/2009/02/08/living-optic-fibres-bypass-the-retinas-incompetent-design/">Living optic fibres bypass the retina’s incompetent design</a></p><p>Many mammals have evolved eyes that can see in the dark. That involves more than just becoming bigger. Their eyes have more light-sensitive rod cells, and these cells have changed at a microscopic level. They have converted the nucleus at the middle of each cell <a href="http://blogs.discovermagazine.com/notrocketscience/2009/04/21/nocturnal-mammals-see-in-dark-by-turning-displaced-dna-into-lenses/">into a light-collecting lens</a>.</p>
<p>In almost all complex cells, DNA is tightly packed around the edge of the nucleus but lightly packed towards its middle. But in the rod cells of nocturnal mammals, it’s the other way round. This inverted arrangement collects light that hits the rod cells and funnels it through to the retina underneath. By moving its DNA around, each cell has become a little optic fibre.</p>
<p><strong>Read more: </strong><a title="Permanent Link: Nocturnal mammals see in dark by turning displaced DNA into lenses" href="http://blogs.discovermagazine.com/notrocketscience/2009/04/21/nocturnal-mammals-see-in-dark-by-turning-displaced-dna-into-lenses/">Nocturnal mammals see in dark by turning displaced DNA into lenses</a></p><p>Like many species that live in perpetual darkness, the <a href="http://blogs.discovermagazine.com/notrocketscience/2010/10/05/cross-breeding-restores-sight-to-blind-cavefish/">blind cavefish has lost its eyes</a>. These fish have evolved from sighted ancestors <a href="http://blogs.discovermagazine.com/notrocketscience/2011/04/07/sleepless-in-mexico-%E2%80%93-three-cavefish-groups-independently-evolved-to-lose-sleep/">on several occasions in</a> different Mexican caves. Their eyes have degenerated over a million years of darkness, but their blindness can be easily reversed by a spot of clever breeding. Many genes govern the development of eyes, and different populations of cavefish have lost their vision by disrupting different eye genes. By breeding individuals from different caves, working genes from one parent can compensate for broken ones from another. The result: babies that can see. (<em>Photo by <a href="http://www.flickr.com/photos/skippy/75380086/sizes/z/in/photostream/">skpy</a></em>)</p>
<p><strong>Read more: </strong><a title="Permanent Link: Cross-breeding restores sight to blind cavefish" href="http://blogs.discovermagazine.com/notrocketscience/2010/10/05/cross-breeding-restores-sight-to-blind-cavefish/">Cross-breeding restores sight to blind cavefish</a></p><p>As babies, flatfishes like plaice and flounders look like every other fish. But as they grow up, one of their eyes moves to the other side of their heads. This allows the adults to lie flat on their sides without getting an eyeful of sand. The evolution of these grotesque fish is <a href="http://blogs.discovermagazine.com/notrocketscience/2008/07/09/early-flatfish-has-eye-thats-moved-halfway-across-its-head/">beautifully captured by a fossil called Heteronectes</a>. It’s a half-committed flatfish. One of its eyes has begun migrating to the other side of its head but hasn’t made it all the way – it stops at the midline. We couldn’t have wished for a better intermediate form – it’s half-way between the standard fish body plan and the distorted visages of flounders and soles.</p>
<p><strong>Read more: </strong><a title="Permanent Link: Early flatfish has eye that’s moved halfway across its head" href="http://blogs.discovermagazine.com/notrocketscience/2008/07/09/early-flatfish-has-eye-thats-moved-halfway-across-its-head/">Early flatfish has eye that’s moved halfway across its head</a></p><p>The Hawaiian bobtail squid creates its own light, using special organs filled with glowing bacteria. But these organs don’t just produce light – <a title="Permanent Link: Glowing squid use bacterial flashlights that double as an extra pair of “eyes”" href="http://blogs.discovermagazine.com/notrocketscience/2009/06/02/glowing-squid-use-bacterial-flashlights-that-double-as-an-extra-pair-of-eyes/">they sense it too</a>. They are loaded with proteins that can detect light, and they produce nervous signals in bright conditions. They can expand and contract like an iris to control how much light gets through. They’re covered with a thick, transparent tissue that acts like a “lens”. The light organs are effectively an extra set of primitive eyes. They are living, ‘seeing’ flashlights. (<strong><em><span style="font-family: &quot;Calibri&quot;,&quot;sans-serif&quot;; font-weight: normal;">Image by </span></em></strong><em>William Ormerod</em>)</p>
<p><strong>Read more: </strong><a title="Permanent Link: Glowing squid use bacterial flashlights that double as an extra pair of “eyes”" href="http://blogs.discovermagazine.com/notrocketscience/2009/06/02/glowing-squid-use-bacterial-flashlights-that-double-as-an-extra-pair-of-eyes/">Glowing squid use bacterial flashlights that double as an extra pair of “eyes”</a></p>
Share

April 27th, 2011 by Ed Yong in Animal behaviour, Animal senses, Animals, Evolution, Eye evolution, Select | 12 comments | RSS feed | Trackback >

12 Responses to “The eyes have it – incredible ways of seeing the world”

  1. 1.   Lee Zimmerman Says:
    April 27th, 2011 at 6:58 pm

    Here are some others for your collection. Eagles have visual pits which act like binoculars. Cheetahs don’t have foveas, instead they have a foveal streak, probably designed to see most acutely along a plane. Most birds seem to have more discerning color vision than we do – instead of three distinct spectrally sensitive cones they have four or more. Pit vipers have infrared sensing organs that are spatially structured like a second pair of eyes.

    Even more amazing than the fact that we can see is that nature seems to have found many different ways of doing it.

  2. 2.   Edward Says:
    April 27th, 2011 at 7:20 pm

    And one more: “The barreleye (Macropinna microstoma) has extremely light-sensitive eyes that can rotate within a transparent, fluid-filled shield on its head…” http://lpb.fieldofscience.com/2009/02/barreleye-fish-macropinna-microstoma.html

  3. 3.   Arwen from the Chameleon's Tongue Says:
    April 28th, 2011 at 12:32 am

    Looks like aquatic creatures are winning the competition for having the weirdest eyes. Fancy chiton even having eyes – they look so primitive.

  4. 4.   jamie Says:
    April 28th, 2011 at 5:52 pm

    So, would the brownsnout spookifish eyes be the first example of a Newtoniam reflector used by animals? No mention of trilobite eyes?

  5. 5.   mckinnley Says:
    April 29th, 2011 at 1:58 pm

    So is there a specific scientific reasoning as 2 why certain col

  6. 6.   amphiox Says:
    April 29th, 2011 at 6:11 pm

    Looks like aquatic creatures are winning the competition for having the weirdest eyes. Fancy chiton even having eyes – they look so primitive.

    That’s most likely just an artifact of the fact the things have been living in aquatic environments for much longer than terrestrial ones. (And many of the terrestrial lineages already had fairly advanced eyes at the point in the time when they first colonized the land….)

  7. 7.   Matt B. Says:
    April 29th, 2011 at 6:40 pm

    Don’t forget the fish with internal eyes and a transparent head.

    When the mantis shrimps acheive sentience and high technology, they’re going to have a hell of a time creating realistic movies.

  8. 8.   Noumenon Says:
    April 30th, 2011 at 10:34 am

    This seems to be the thread where this comment should have gone, the other one is empty.

    In the animal kingdom, eyes have evolved dozens of times.

    This kind of took me aback. Are eyes especially notable for this? I don’t think you’d say livers or lungs have evolved dozens of times. Do you mean that eyes evolved in multiple eyeless animals, or just that evolution produced multiple different kinds of eyes?

  9. 9.   Noumenon Says:
    May 1st, 2011 at 1:57 am

    Is there anything else you would say evolved “dozens of times”? I only see a couple different kinds of wings, a couple different kinds of teeth, et cetera. Venom is something I could say evolved many times.

  10. 10.   Ed Yong Says:
    May 1st, 2011 at 4:21 pm

    “Do you mean that eyes evolved in multiple eyeless animals, or just that evolution produced multiple different kinds of eyes?”

    Both.

    “Is there anything else you would say evolved “dozens of times”?”

    Yep, venom is a good example. Also asexuality, bioluminescence, armour, sociality, flightlessness, gliding…

  11. 11.   dave chamberlin Says:
    May 5th, 2011 at 4:07 pm

    There is a science book out called ‘In the blink of an eye; how vision kick started the big bang of evolution” by Andrew Parker. He argues that vision happened precisely 543 million years ago and kick started the Cambrian Explosion. I don’t buy his hypothesis, for one thing if vision evolved dozens of times it is damned unlikely it all happened at the same time. Ed Yong have you read this this book, or started it and decided you had better things to do.

  12. 12.   Ed Yong Says:
    May 6th, 2011 at 9:29 am

    Parker’s hypothesis doesn’t suggest that all eyes evolved at the same time; rather, it suggests that the first eyes (and really, the first image-forming eyes) triggered a runaway evolutionary arms race between predator and prey. So the repeated evolution of vision doesn’t disprove his idea. That being said, I don’t buy it. Parker’s explanation always struck me as being a bit human-centric. It makes too much of the importance of vision and downplays the importance of other senses, which can provide substantial amounts of information over longer distances.

    Parker’s latest book also suggests that the stories of the Book of Genesis are surprisingly accurate and accord with science, which doesn’t really instil confidence in the rest of his ideas.

Leave a Reply





    • About Not Exactly Rocket Science



      Ed Yong is an award-winning British science writer. His work has appeared in New Scientist, the Times, WIRED, the Guardian, Nature and more. Not Exactly Rocket Science is his attempt to talk about the awe-inspiring, beautiful and quirky world of science to as many people as possible.

      My personal website with biography, other writing, speaking engagements, and more

      Some interviews with me
      Some awards that I’ve won
      Who my readers are: 2008, 2009 and 2010 editions
      A complete list of posts from this blog

      Follow me on Twitter or Google+

      Contact me on edyong209[at]googlemail[dot]com

    • Support

    • What others say

      "One of the best sites for in-depth analysis of interesting scientific papers" - The Times

      "One of the smartest science bloggers I read... a prime practitioner among the new generation of scientifically authoritative bloggers" - David Rowan, editor of Wired UK

      "Engaging and jargon-free multimedia storytelling about science and the digital age" - National Academy of Sciences

      "A consistently illuminating home for long, thoughtful, and thorough explorations of science news" - National Association of Science Writers

      "Head and shoulders above many broadsheet hacks" - Ben Goldacre

      "Ed Yong... is made of pure unobtanium and rides TWO Toruks." - Frank Swain

      "Ed Yong is better than chocolate, fairy lights, and kittens chasing yarn. That is all." - Christine Ottery

    • Do you want to be a science writer?

      Read origin stories and advice from over 130 science writers from around the world.
    • Not Exactly Rocket Science content

      RSS Recent Posts

      Recent Posts

      • I’ve got your missing links right here (26 May 2012)
      • Neurons transplanted into mouse spines reverse chronic pain
      • Virtual resurrection shows that early four-legged animal couldn’t walk very well
      • New sense organ helps giant whales to coordinate the world’s biggest mouthfuls
      • Here’s where all the magic happens
      • Blind mice regain sight after scientists persuade their optic nerves to grow
      • I’ve got your missing links right here (19 May 2012)
      • Meet the paralysed woman who commandeered a robotic arm
      Categories

      Categories

      Archives

      Archives

      • May 2012
      • April 2012
      • March 2012
      • February 2012
      • January 2012
      • December 2011
      • November 2011
      • October 2011
      • September 2011
      • August 2011
      • July 2011
      • June 2011
      • May 2011
      • April 2011
      • March 2011
      • February 2011
      • January 2011
      • December 2010
      • November 2010
      • October 2010
      • September 2010
      • August 2010
      • July 2010
      • June 2010
      • May 2010
      • April 2010
      • March 2010
      • February 2010
      • January 2010
      • December 2009
      • November 2009
      • October 2009
      • September 2009
      • August 2009
      • July 2009
      • June 2009
      • May 2009
      • April 2009
      • March 2009
      • February 2009
      • January 2009
      • December 2008
      • November 2008
      • October 2008
      • September 2008
      • August 2008
      • July 2008
      • June 2008
      • May 2008
      • April 2008
      • March 2008
      • February 2008
    • RSS Twitter

    • My wife, who makes it all possible

      Alice.jpg
    • Blogroll

      Science blogs

      Science blogs

      • 80 Beats
      • A Blog Around the Clock
      • Adventures in Ethics and Science
      • Aetiology
      • Alice Bell
      • Ars Technica
      • Arthropoda
      • Atlantic Science
      • Babel's Dawn
      • Bad Astronomy
      • Bad Science
      • BPS Research Digest Blog
      • Cancer Research UK Science Update Blog
      • Child's Play
      • Cocktail Party Physics
      • Collision Detection
      • Culture Dish
      • Culturing Science
      • Deep Sea News
      • Discoblog + NCBI ROFL
      • Dot Earth
      • Dr Petra Boynton
      • Drugmonkey
      • EarthLab
      • Embargo Watch
      • Epiphenom
      • Evolving Thoughts
      • Finite Attention Span
      • Fistful of Science
      • Gary Schwitzer's HealthNewsReview
      • Gene Expression
      • Genetic Future
      • Genomeboy
      • Genomicron
      • Gimpy's Blog
      • Highly Allochthonous
      • Ionian Enchantment
      • JL Vernon Presents American Psico
      • Joanne Loves Science
      • John Pavlus
      • Just a Theory
      • Lab Rat
      • Laelaps
      • Last Word on Nothing
      • Lay Scientist
      • Loom
      • Mark Changizi
      • Mind Hacks
      • Myrmecos
      • Neuroanthropology
      • Neurologica
      • Neuron Culture
      • Neurophilosophy
      • Neurotic Physiology (SciCurious)
      • Neurotribes
      • Obesity Panacea
      • Observations of a Nerd
      • On Becoming a Domestic and Laboratory Goddess
      • Open Minds and Parachutes
      • Political Science (Evan Harris)
      • Predictably Irrational
      • Retraction Watch
      • Save Your Breath for Running Ponies
      • Schooner of Science
      • Science Punk
      • ScienceLine
      • ScienceLush
      • Sentence First
      • Sex, Drugs and Rockin' Venom – Confessions of an Extreme Scientist
      • Skepchick
      • Speakeasy Science
      • Superbug
      • Take as Directed
      • Terra Sigillata
      • Tetrapod Zoology
      • The Artful Amoeba
      • The Chicken or the Egg
      • The Examining Room of Dr Charles
      • The Flying Trilobite
      • The Frontal Cortex
      • The Gleaming Retort
      • The Great Beyond
      • The Intersection
      • The Inverse Square Blog
      • The Millikan Daily
      • The Primate Diaries
      • The Science Project
      • Thoughtomics
      • Thus Spake Zuska
      • TYWKIWDBI
      • Vagina Dentata
      • Voyages Around my Camera
      • Weird Bug Lady
      • White Coat Underground
      • Why Evolution is True
      • Wild Muse
      • Wired Science
      • Words of Science
      • XKCD
      • Zooillogix
      Other blogs

      Other blogs

      • Cafe Philos
      • Miss Cellania
    • NetworkedBlogs
      Blog:
      Not Exactly Rocket Science
      Topics:
      science, biology, news
       
      Follow my blog


  • Kalmbach Publishing Co.

    Copyright © 2012, Kalmbach Publishing Co.

    Privacy - Terms - Reader Services - Subscribe Today - Advertise - About Us