full transcript

From the Ted Talk by Joshua Harvey: The evolution of the human eye

Unscramble the Blue Letters

The human eye is an amazing mechanism, able to detect anywhere from a few pnohtos to direct sunlight, or switch focus from the screen in front of you to the distant horizon in a third of a second. In fact, the structures required for such incredible flexibility were once considered so complex that Charles diwran himself acknowledged that the idea of there having evolved seemed absurd in the highest possible degree. And yet, that is exactly what hepenapd, starting more than 500 million years ago. The story of the human eye begnis with a simple light spot, such as the one found in single-celled organisms, like euglena. This is a csutler of light-sensitive pntreois linked to the organism's flagellum, activating when it fndis light and, therefore, food. A more complex veoirsn of this light spot can be found in the flat worm, planaria. Being cupped, rather than flat, enables it to better sense the direction of the incoming light. Among its other uses, this aibltiy allows an organism to seek out shade and hide from predators. Over the millenia, as such light cups grew deeper in some organisms, the oepning at the front grew smaller. The result was a pinhole effect, which increased resolution dramatically, reducing distortion by only allowing a thin beam of light into the eye. The nautilus, an aosectnr of the octopus, uses this pinhole eye for ipovrmed resolution and directional ssineng. Although the pinhole eye allows for simple images, the key step towards the eye as we know it is a lens. This is thought to have evolved through transparent clels covering the opening to prevent infection, aiollnwg the inside of the eye to fill with fluid that optimizes light sensitivity and processing. Crystalline proteins forming at the surface created a structure that proved useful in focusing lgiht at a single point on the retina. It is this lens that is the key to the eye's adaptability, cghannig its curvature to apdat to near and far vision. This structure of the pinhole camera with a lens served as the bisas for what would ellntvuaey evolve into the human eye. Further refinements would include a colored ring, called the iris, that coolrtns the amount of light entering the eye, a tguoh white outer layer, known as the scelra, to maintain its structure, and tear glands that secrete a ptevrtocie film. But equally important was the annoiympcacg evolution of the brain, with its expansion of the visual cortex to process the sharper and more colorful images it was receiving. We now know that far from being an ideal metpcsariee of design, our eye bares traces of its step by step evolution. For example, the huamn retina is inverted, with light-detecting cells facing away from the eye opening. This results in a blind spot, where the opitc nerve must pierce the retina to recah the photosensitive layer in the back. The similar looking eyes of cephalopods, which evolved independently, have a front-facing rentia, allowing them to see without a blind spot. Other creatures' eyes display different adaptations. Anableps, the so clelad four-eyed fish, have eyes divided in two scoentis for looking above and under wtaer, perfect for spotting both predators and prey. Cats, classically nighttime hetrnus, have evolved with a reflective layer maximizing the amount of light the eye can dtceet, granting them excellent night viiosn, as well as their signature glow. These are just a few examples of the huge diversity of eyes in the animal kingdom. So if you could design an eye, would you do it any differently? This question isn't as strange as it might sound. Today, dortcos and scientists are looking at different eye structures to help digesn baceiihcnoaml implants for the vision iarpemid. And in the not so distant future, the machines built with the precision and flexibilty of the human eye may even eanlbe it to surpass its own evolution.

Open Cloze

The human eye is an amazing mechanism, able to detect anywhere from a few _______ to direct sunlight, or switch focus from the screen in front of you to the distant horizon in a third of a second. In fact, the structures required for such incredible flexibility were once considered so complex that Charles ______ himself acknowledged that the idea of there having evolved seemed absurd in the highest possible degree. And yet, that is exactly what ________, starting more than 500 million years ago. The story of the human eye ______ with a simple light spot, such as the one found in single-celled organisms, like euglena. This is a _______ of light-sensitive ________ linked to the organism's flagellum, activating when it _____ light and, therefore, food. A more complex _______ of this light spot can be found in the flat worm, planaria. Being cupped, rather than flat, enables it to better sense the direction of the incoming light. Among its other uses, this _______ allows an organism to seek out shade and hide from predators. Over the millenia, as such light cups grew deeper in some organisms, the _______ at the front grew smaller. The result was a pinhole effect, which increased resolution dramatically, reducing distortion by only allowing a thin beam of light into the eye. The nautilus, an ________ of the octopus, uses this pinhole eye for ________ resolution and directional _______. Although the pinhole eye allows for simple images, the key step towards the eye as we know it is a lens. This is thought to have evolved through transparent _____ covering the opening to prevent infection, ________ the inside of the eye to fill with fluid that optimizes light sensitivity and processing. Crystalline proteins forming at the surface created a structure that proved useful in focusing _____ at a single point on the retina. It is this lens that is the key to the eye's adaptability, ________ its curvature to _____ to near and far vision. This structure of the pinhole camera with a lens served as the _____ for what would __________ evolve into the human eye. Further refinements would include a colored ring, called the iris, that ________ the amount of light entering the eye, a _____ white outer layer, known as the ______, to maintain its structure, and tear glands that secrete a __________ film. But equally important was the ____________ evolution of the brain, with its expansion of the visual cortex to process the sharper and more colorful images it was receiving. We now know that far from being an ideal ___________ of design, our eye bares traces of its step by step evolution. For example, the _____ retina is inverted, with light-detecting cells facing away from the eye opening. This results in a blind spot, where the _____ nerve must pierce the retina to _____ the photosensitive layer in the back. The similar looking eyes of cephalopods, which evolved independently, have a front-facing ______, allowing them to see without a blind spot. Other creatures' eyes display different adaptations. Anableps, the so ______ four-eyed fish, have eyes divided in two ________ for looking above and under _____, perfect for spotting both predators and prey. Cats, classically nighttime _______, have evolved with a reflective layer maximizing the amount of light the eye can ______, granting them excellent night ______, as well as their signature glow. These are just a few examples of the huge diversity of eyes in the animal kingdom. So if you could design an eye, would you do it any differently? This question isn't as strange as it might sound. Today, _______ and scientists are looking at different eye structures to help ______ _____________ implants for the vision ________. And in the not so distant future, the machines built with the precision and flexibilty of the human eye may even ______ it to surpass its own evolution.

Solution

  1. eventually
  2. hunters
  3. basis
  4. impaired
  5. tough
  6. biomechanical
  7. optic
  8. human
  9. allowing
  10. adapt
  11. masterpiece
  12. changing
  13. reach
  14. finds
  15. sensing
  16. retina
  17. opening
  18. version
  19. ancestor
  20. photons
  21. darwin
  22. doctors
  23. happened
  24. cluster
  25. protective
  26. sections
  27. water
  28. improved
  29. accompanying
  30. enable
  31. light
  32. proteins
  33. begins
  34. controls
  35. detect
  36. called
  37. vision
  38. ability
  39. design
  40. cells
  41. sclera

Original Text

The human eye is an amazing mechanism, able to detect anywhere from a few photons to direct sunlight, or switch focus from the screen in front of you to the distant horizon in a third of a second. In fact, the structures required for such incredible flexibility were once considered so complex that Charles Darwin himself acknowledged that the idea of there having evolved seemed absurd in the highest possible degree. And yet, that is exactly what happened, starting more than 500 million years ago. The story of the human eye begins with a simple light spot, such as the one found in single-celled organisms, like euglena. This is a cluster of light-sensitive proteins linked to the organism's flagellum, activating when it finds light and, therefore, food. A more complex version of this light spot can be found in the flat worm, planaria. Being cupped, rather than flat, enables it to better sense the direction of the incoming light. Among its other uses, this ability allows an organism to seek out shade and hide from predators. Over the millenia, as such light cups grew deeper in some organisms, the opening at the front grew smaller. The result was a pinhole effect, which increased resolution dramatically, reducing distortion by only allowing a thin beam of light into the eye. The nautilus, an ancestor of the octopus, uses this pinhole eye for improved resolution and directional sensing. Although the pinhole eye allows for simple images, the key step towards the eye as we know it is a lens. This is thought to have evolved through transparent cells covering the opening to prevent infection, allowing the inside of the eye to fill with fluid that optimizes light sensitivity and processing. Crystalline proteins forming at the surface created a structure that proved useful in focusing light at a single point on the retina. It is this lens that is the key to the eye's adaptability, changing its curvature to adapt to near and far vision. This structure of the pinhole camera with a lens served as the basis for what would eventually evolve into the human eye. Further refinements would include a colored ring, called the iris, that controls the amount of light entering the eye, a tough white outer layer, known as the sclera, to maintain its structure, and tear glands that secrete a protective film. But equally important was the accompanying evolution of the brain, with its expansion of the visual cortex to process the sharper and more colorful images it was receiving. We now know that far from being an ideal masterpiece of design, our eye bares traces of its step by step evolution. For example, the human retina is inverted, with light-detecting cells facing away from the eye opening. This results in a blind spot, where the optic nerve must pierce the retina to reach the photosensitive layer in the back. The similar looking eyes of cephalopods, which evolved independently, have a front-facing retina, allowing them to see without a blind spot. Other creatures' eyes display different adaptations. Anableps, the so called four-eyed fish, have eyes divided in two sections for looking above and under water, perfect for spotting both predators and prey. Cats, classically nighttime hunters, have evolved with a reflective layer maximizing the amount of light the eye can detect, granting them excellent night vision, as well as their signature glow. These are just a few examples of the huge diversity of eyes in the animal kingdom. So if you could design an eye, would you do it any differently? This question isn't as strange as it might sound. Today, doctors and scientists are looking at different eye structures to help design biomechanical implants for the vision impaired. And in the not so distant future, the machines built with the precision and flexibilty of the human eye may even enable it to surpass its own evolution.

Frequently Occurring Word Combinations

ngrams of length 2

collocation frequency
human eye 4
pinhole eye 2

Important Words

  1. ability
  2. absurd
  3. accompanying
  4. acknowledged
  5. activating
  6. adapt
  7. adaptability
  8. adaptations
  9. allowing
  10. amazing
  11. amount
  12. anableps
  13. ancestor
  14. animal
  15. bares
  16. basis
  17. beam
  18. begins
  19. biomechanical
  20. blind
  21. brain
  22. built
  23. called
  24. camera
  25. cats
  26. cells
  27. cephalopods
  28. changing
  29. charles
  30. classically
  31. cluster
  32. colored
  33. colorful
  34. complex
  35. considered
  36. controls
  37. cortex
  38. covering
  39. created
  40. crystalline
  41. cupped
  42. cups
  43. curvature
  44. darwin
  45. deeper
  46. degree
  47. design
  48. detect
  49. differently
  50. direct
  51. direction
  52. directional
  53. display
  54. distant
  55. distortion
  56. diversity
  57. divided
  58. doctors
  59. dramatically
  60. effect
  61. enable
  62. enables
  63. entering
  64. equally
  65. euglena
  66. eventually
  67. evolution
  68. evolve
  69. evolved
  70. examples
  71. excellent
  72. expansion
  73. eye
  74. eyes
  75. facing
  76. fact
  77. fill
  78. film
  79. finds
  80. fish
  81. flagellum
  82. flat
  83. flexibility
  84. flexibilty
  85. fluid
  86. focus
  87. focusing
  88. food
  89. forming
  90. front
  91. future
  92. glands
  93. glow
  94. granting
  95. grew
  96. happened
  97. hide
  98. highest
  99. horizon
  100. huge
  101. human
  102. hunters
  103. idea
  104. ideal
  105. images
  106. impaired
  107. implants
  108. important
  109. improved
  110. include
  111. incoming
  112. increased
  113. incredible
  114. independently
  115. infection
  116. inverted
  117. iris
  118. key
  119. kingdom
  120. layer
  121. lens
  122. light
  123. linked
  124. machines
  125. maintain
  126. masterpiece
  127. maximizing
  128. mechanism
  129. millenia
  130. million
  131. nautilus
  132. nerve
  133. night
  134. nighttime
  135. octopus
  136. opening
  137. optic
  138. optimizes
  139. organism
  140. organisms
  141. outer
  142. perfect
  143. photons
  144. photosensitive
  145. pierce
  146. pinhole
  147. planaria
  148. point
  149. precision
  150. predators
  151. prevent
  152. prey
  153. process
  154. processing
  155. protective
  156. proteins
  157. proved
  158. question
  159. reach
  160. receiving
  161. reducing
  162. refinements
  163. reflective
  164. required
  165. resolution
  166. result
  167. results
  168. retina
  169. ring
  170. scientists
  171. sclera
  172. screen
  173. secrete
  174. sections
  175. seek
  176. sense
  177. sensing
  178. sensitivity
  179. served
  180. shade
  181. sharper
  182. signature
  183. similar
  184. simple
  185. single
  186. smaller
  187. sound
  188. spot
  189. spotting
  190. starting
  191. step
  192. story
  193. strange
  194. structure
  195. structures
  196. sunlight
  197. surface
  198. surpass
  199. switch
  200. tear
  201. thin
  202. thought
  203. today
  204. tough
  205. traces
  206. transparent
  207. version
  208. vision
  209. visual
  210. water
  211. white
  212. worm
  213. years