full transcript

From the Ted Talk by Dorsa Amir: Why do humans have a third eyelid?

Unscramble the Blue Letters


To answer this question, it helps to usdnenratd natural selection. Natural selection simply means that traits which help an organism survive and reproduce in a given environment are more likely to make it to the next generation. As the environment changes, traits that were once useful can become huafrml. Those traits are often sceteled against, meaning they gulaadlry disappear from the puapoltion. But if a trait isn’t actively harmful, it might not get selected against, and stick around even though it isn’t useful.

Take the tailbone. Evolutionary biologists think that as the climate got drier and grasslands popped up, our tail-bearing ancestors left the trees and started wklinag on land. The tials that had hepeld them in the trees began to disrupt their ability to walk on land. So iilivadndus with mutations that rdueced the lgtenh of their tails became more successful at life on land, surviving long enough to pass their short tails on to the next generation. The change was likely gradual over millions of yaers until, about 20 million years ago, our ancestors’ external tails disappeared altogether. Today, we know hmuan embryos have tails that dissolve as the embryo develops. But the stubby tailbone sticks around, probably because it doesn’t cause any harm— in fact, it serves a more minor fcoutnin as the anchor point for certain other muscles.

Open Cloze


To answer this question, it helps to __________ natural selection. Natural selection simply means that traits which help an organism survive and reproduce in a given environment are more likely to make it to the next generation. As the environment changes, traits that were once useful can become _______. Those traits are often ________ against, meaning they _________ disappear from the __________. But if a trait isn’t actively harmful, it might not get selected against, and stick around even though it isn’t useful.

Take the tailbone. Evolutionary biologists think that as the climate got drier and grasslands popped up, our tail-bearing ancestors left the trees and started _______ on land. The _____ that had ______ them in the trees began to disrupt their ability to walk on land. So ___________ with mutations that _______ the ______ of their tails became more successful at life on land, surviving long enough to pass their short tails on to the next generation. The change was likely gradual over millions of _____ until, about 20 million years ago, our ancestors’ external tails disappeared altogether. Today, we know _____ embryos have tails that dissolve as the embryo develops. But the stubby tailbone sticks around, probably because it doesn’t cause any harm— in fact, it serves a more minor ________ as the anchor point for certain other muscles.

Solution


  1. tails
  2. human
  3. individuals
  4. understand
  5. helped
  6. years
  7. gradually
  8. reduced
  9. selected
  10. walking
  11. population
  12. harmful
  13. length
  14. function

Original Text


To answer this question, it helps to understand natural selection. Natural selection simply means that traits which help an organism survive and reproduce in a given environment are more likely to make it to the next generation. As the environment changes, traits that were once useful can become harmful. Those traits are often selected against, meaning they gradually disappear from the population. But if a trait isn’t actively harmful, it might not get selected against, and stick around even though it isn’t useful.

Take the tailbone. Evolutionary biologists think that as the climate got drier and grasslands popped up, our tail-bearing ancestors left the trees and started walking on land. The tails that had helped them in the trees began to disrupt their ability to walk on land. So individuals with mutations that reduced the length of their tails became more successful at life on land, surviving long enough to pass their short tails on to the next generation. The change was likely gradual over millions of years until, about 20 million years ago, our ancestors’ external tails disappeared altogether. Today, we know human embryos have tails that dissolve as the embryo develops. But the stubby tailbone sticks around, probably because it doesn’t cause any harm— in fact, it serves a more minor function as the anchor point for certain other muscles.

Frequently Occurring Word Combinations


ngrams of length 2

collocation frequency
natural selection 2
intestinal system 2


Important Words


  1. ability
  2. actively
  3. altogether
  4. ancestors
  5. anchor
  6. answer
  7. began
  8. biologists
  9. change
  10. climate
  11. develops
  12. disappear
  13. disappeared
  14. disrupt
  15. dissolve
  16. drier
  17. embryo
  18. embryos
  19. environment
  20. evolutionary
  21. external
  22. fact
  23. function
  24. generation
  25. gradual
  26. gradually
  27. grasslands
  28. harmful
  29. helped
  30. helps
  31. human
  32. individuals
  33. land
  34. left
  35. length
  36. life
  37. long
  38. meaning
  39. means
  40. million
  41. millions
  42. minor
  43. muscles
  44. mutations
  45. natural
  46. organism
  47. pass
  48. point
  49. popped
  50. population
  51. question
  52. reduced
  53. reproduce
  54. selected
  55. selection
  56. serves
  57. short
  58. simply
  59. started
  60. stick
  61. sticks
  62. stubby
  63. successful
  64. survive
  65. surviving
  66. tailbone
  67. tails
  68. today
  69. trait
  70. traits
  71. trees
  72. understand
  73. walk
  74. walking
  75. years