full transcript

From the Ted Talk by Daniel M. Abrams: Why are some people left-handed?

Unscramble the Blue Letters

If you know an older left-handed person, chances are they had to learn to write or eat with their right hand. And in many parts of the world, it's still cmomon practice to force children to use their "proper" hand. Even the word for right also means correct or good, not just in English, but many other languages, too. But if being left-handed is so wrong, then why does it happen in the first place? toady, about 1/10 of the world's poitlaopun are left-handed. Archeological evidence sohws that it's been that way for as long as 500,000 years, with about 10% of human remains showing the associated differences in arm length and bone dsniety, and some ancient tools and artifacts showing evidence of left-hand use. And despite what many may think, handedness is not a choice. It can be predicted even before birth based on the fetus' position in the womb. So, if handedness is inborn, does that mean it's genetic? Well, yes and no. Identical twins, who have the same genes, can have different dominant hands. In fact, this happens as often as it does with any other sibling pair. But the chances of being right or left-handed are determined by the handedness of your parents in surprisingly consistent ratios. If your father was left-handed but your mother was right-handed, you have a 17% chance of being born left-handed, while two righties will have a left-handed child only 10% of the time. Handedness seems to be determined by a roll of the dice, but the odds are set by your genes. All of this implies there's a reason that evolution has produced this small proportion of lefties, and maintained it over the course of millennia. And while there have been several theories amntitpteg to explain why handedness exists in the first place, or why most people are right-handed, a recent mathematical model suggests that the auctal ratio reflects a balance between competitive and cooperative pressures on human evolution. The benefits of being left-handed are clearest in activities involving an opponent, like coambt or cmtopiivtee soprts. For example, about 50% of top hitters in baseball have been left-handed. Why? Think of it as a ssuiprre advantage. Because lefties are a minority to begin with, both right-handed and left-handed cotormtpies will spend most of their time eitnncunreog and piacrnticg against righties. So when the two face each other, the left-hander will be better prepared against this right-handed opponent, while the rhtigy will be thrown off. This fighting hispteyohs, where an imbalance in the population results in an aavgtnade for left-handed fighters or athletes, is an example of neitvgae frequency-dependent stlcieeon. But according to the principles of evolution, gupros that have a relative advantage tend to grow until that advantage disappears. If people were only fighting and competing throughout human evolution, natural selection would lead to more lfeetis being the ones that made it until there were so many of them, that it was no longer a rare asset. So in a peruly competitive wrlod, 50% of the population would be left-handed. But human evolution has been shaped by coeoartpion, as well as competition. And cooperative pressure pshues handedness distribution in the opposite diroeitcn. In golf, where performance doesn't dpened on the opponent, only 4% of top players are left-handed, an example of the wider phenomenon of tool sharing. Just as young potential golfers can more easily find a set of right-handed cubls, many of the ianpomrtt instruments that have shaped scoiety were designed for the right-handed majority. Because lefties are worse at using these tools, and suffer from higher accident rates, they would be less successful in a purely cooperative world, eventually disappearing from the population. So by correctly prinetdicg the distribution of left-handed people in the general population, as well as matching data from various sports, the model indicates that the pecsrnisete of lefties as a smlal but stable mrnoitiy reecflts an equilibrium that comes from competitive and crtopaioeve effects playing out sutollmsauniey over time. And the most intriguing thing is what the numbers can tell us about various populations. From the skewed distribution of pawedness in cooperative animals, to the slightly larger percentage of lefties in competitive hunter-gatherer sioietecs, we may even find that the answers to some puzzles of early human evolution are already in our hands.

Open Cloze

If you know an older left-handed person, chances are they had to learn to write or eat with their right hand. And in many parts of the world, it's still ______ practice to force children to use their "proper" hand. Even the word for right also means correct or good, not just in English, but many other languages, too. But if being left-handed is so wrong, then why does it happen in the first place? _____, about 1/10 of the world's __________ are left-handed. Archeological evidence _____ that it's been that way for as long as 500,000 years, with about 10% of human remains showing the associated differences in arm length and bone _______, and some ancient tools and artifacts showing evidence of left-hand use. And despite what many may think, handedness is not a choice. It can be predicted even before birth based on the fetus' position in the womb. So, if handedness is inborn, does that mean it's genetic? Well, yes and no. Identical twins, who have the same genes, can have different dominant hands. In fact, this happens as often as it does with any other sibling pair. But the chances of being right or left-handed are determined by the handedness of your parents in surprisingly consistent ratios. If your father was left-handed but your mother was right-handed, you have a 17% chance of being born left-handed, while two righties will have a left-handed child only 10% of the time. Handedness seems to be determined by a roll of the dice, but the odds are set by your genes. All of this implies there's a reason that evolution has produced this small proportion of lefties, and maintained it over the course of millennia. And while there have been several theories __________ to explain why handedness exists in the first place, or why most people are right-handed, a recent mathematical model suggests that the ______ ratio reflects a balance between competitive and cooperative pressures on human evolution. The benefits of being left-handed are clearest in activities involving an opponent, like ______ or ___________ ______. For example, about 50% of top hitters in baseball have been left-handed. Why? Think of it as a ________ advantage. Because lefties are a minority to begin with, both right-handed and left-handed ___________ will spend most of their time ____________ and __________ against righties. So when the two face each other, the left-hander will be better prepared against this right-handed opponent, while the ______ will be thrown off. This fighting __________, where an imbalance in the population results in an _________ for left-handed fighters or athletes, is an example of ________ frequency-dependent _________. But according to the principles of evolution, ______ that have a relative advantage tend to grow until that advantage disappears. If people were only fighting and competing throughout human evolution, natural selection would lead to more _______ being the ones that made it until there were so many of them, that it was no longer a rare asset. So in a ______ competitive _____, 50% of the population would be left-handed. But human evolution has been shaped by ___________, as well as competition. And cooperative pressure ______ handedness distribution in the opposite _________. In golf, where performance doesn't ______ on the opponent, only 4% of top players are left-handed, an example of the wider phenomenon of tool sharing. Just as young potential golfers can more easily find a set of right-handed _____, many of the _________ instruments that have shaped _______ were designed for the right-handed majority. Because lefties are worse at using these tools, and suffer from higher accident rates, they would be less successful in a purely cooperative world, eventually disappearing from the population. So by correctly __________ the distribution of left-handed people in the general population, as well as matching data from various sports, the model indicates that the ___________ of lefties as a _____ but stable ________ ________ an equilibrium that comes from competitive and ___________ effects playing out ______________ over time. And the most intriguing thing is what the numbers can tell us about various populations. From the skewed distribution of pawedness in cooperative animals, to the slightly larger percentage of lefties in competitive hunter-gatherer _________, we may even find that the answers to some puzzles of early human evolution are already in our hands.

Solution

  1. purely
  2. groups
  3. selection
  4. sports
  5. advantage
  6. today
  7. world
  8. cooperative
  9. negative
  10. societies
  11. society
  12. clubs
  13. combat
  14. hypothesis
  15. common
  16. practicing
  17. lefties
  18. important
  19. competitors
  20. righty
  21. direction
  22. shows
  23. small
  24. persistence
  25. actual
  26. density
  27. simultaneously
  28. surprise
  29. population
  30. attempting
  31. reflects
  32. predicting
  33. pushes
  34. competitive
  35. cooperation
  36. depend
  37. encountering
  38. minority

Original Text

If you know an older left-handed person, chances are they had to learn to write or eat with their right hand. And in many parts of the world, it's still common practice to force children to use their "proper" hand. Even the word for right also means correct or good, not just in English, but many other languages, too. But if being left-handed is so wrong, then why does it happen in the first place? Today, about 1/10 of the world's population are left-handed. Archeological evidence shows that it's been that way for as long as 500,000 years, with about 10% of human remains showing the associated differences in arm length and bone density, and some ancient tools and artifacts showing evidence of left-hand use. And despite what many may think, handedness is not a choice. It can be predicted even before birth based on the fetus' position in the womb. So, if handedness is inborn, does that mean it's genetic? Well, yes and no. Identical twins, who have the same genes, can have different dominant hands. In fact, this happens as often as it does with any other sibling pair. But the chances of being right or left-handed are determined by the handedness of your parents in surprisingly consistent ratios. If your father was left-handed but your mother was right-handed, you have a 17% chance of being born left-handed, while two righties will have a left-handed child only 10% of the time. Handedness seems to be determined by a roll of the dice, but the odds are set by your genes. All of this implies there's a reason that evolution has produced this small proportion of lefties, and maintained it over the course of millennia. And while there have been several theories attempting to explain why handedness exists in the first place, or why most people are right-handed, a recent mathematical model suggests that the actual ratio reflects a balance between competitive and cooperative pressures on human evolution. The benefits of being left-handed are clearest in activities involving an opponent, like combat or competitive sports. For example, about 50% of top hitters in baseball have been left-handed. Why? Think of it as a surprise advantage. Because lefties are a minority to begin with, both right-handed and left-handed competitors will spend most of their time encountering and practicing against righties. So when the two face each other, the left-hander will be better prepared against this right-handed opponent, while the righty will be thrown off. This fighting hypothesis, where an imbalance in the population results in an advantage for left-handed fighters or athletes, is an example of negative frequency-dependent selection. But according to the principles of evolution, groups that have a relative advantage tend to grow until that advantage disappears. If people were only fighting and competing throughout human evolution, natural selection would lead to more lefties being the ones that made it until there were so many of them, that it was no longer a rare asset. So in a purely competitive world, 50% of the population would be left-handed. But human evolution has been shaped by cooperation, as well as competition. And cooperative pressure pushes handedness distribution in the opposite direction. In golf, where performance doesn't depend on the opponent, only 4% of top players are left-handed, an example of the wider phenomenon of tool sharing. Just as young potential golfers can more easily find a set of right-handed clubs, many of the important instruments that have shaped society were designed for the right-handed majority. Because lefties are worse at using these tools, and suffer from higher accident rates, they would be less successful in a purely cooperative world, eventually disappearing from the population. So by correctly predicting the distribution of left-handed people in the general population, as well as matching data from various sports, the model indicates that the persistence of lefties as a small but stable minority reflects an equilibrium that comes from competitive and cooperative effects playing out simultaneously over time. And the most intriguing thing is what the numbers can tell us about various populations. From the skewed distribution of pawedness in cooperative animals, to the slightly larger percentage of lefties in competitive hunter-gatherer societies, we may even find that the answers to some puzzles of early human evolution are already in our hands.

Frequently Occurring Word Combinations

ngrams of length 2

collocation frequency
human evolution 3

Important Words

  1. accident
  2. activities
  3. actual
  4. advantage
  5. ancient
  6. animals
  7. answers
  8. archeological
  9. arm
  10. artifacts
  11. asset
  12. athletes
  13. attempting
  14. balance
  15. baseball
  16. based
  17. benefits
  18. birth
  19. bone
  20. born
  21. chance
  22. chances
  23. child
  24. children
  25. choice
  26. clearest
  27. clubs
  28. combat
  29. common
  30. competing
  31. competition
  32. competitive
  33. competitors
  34. consistent
  35. cooperation
  36. cooperative
  37. correct
  38. correctly
  39. data
  40. density
  41. depend
  42. designed
  43. determined
  44. dice
  45. differences
  46. direction
  47. disappearing
  48. disappears
  49. distribution
  50. dominant
  51. early
  52. easily
  53. eat
  54. effects
  55. encountering
  56. english
  57. equilibrium
  58. eventually
  59. evidence
  60. evolution
  61. exists
  62. explain
  63. face
  64. fact
  65. father
  66. fighters
  67. fighting
  68. find
  69. force
  70. general
  71. genes
  72. genetic
  73. golf
  74. golfers
  75. good
  76. groups
  77. grow
  78. hand
  79. handedness
  80. hands
  81. happen
  82. higher
  83. hitters
  84. human
  85. hypothesis
  86. identical
  87. imbalance
  88. implies
  89. important
  90. inborn
  91. instruments
  92. intriguing
  93. involving
  94. languages
  95. larger
  96. lead
  97. learn
  98. lefties
  99. length
  100. long
  101. longer
  102. maintained
  103. majority
  104. matching
  105. mathematical
  106. means
  107. millennia
  108. minority
  109. model
  110. mother
  111. natural
  112. negative
  113. numbers
  114. odds
  115. older
  116. opponent
  117. pair
  118. parents
  119. parts
  120. pawedness
  121. people
  122. percentage
  123. performance
  124. persistence
  125. person
  126. phenomenon
  127. place
  128. players
  129. playing
  130. population
  131. populations
  132. position
  133. potential
  134. practice
  135. practicing
  136. predicted
  137. predicting
  138. prepared
  139. pressure
  140. pressures
  141. principles
  142. produced
  143. proportion
  144. purely
  145. pushes
  146. puzzles
  147. rare
  148. rates
  149. ratio
  150. ratios
  151. reason
  152. reflects
  153. relative
  154. remains
  155. results
  156. righties
  157. righty
  158. roll
  159. selection
  160. set
  161. shaped
  162. sharing
  163. showing
  164. shows
  165. sibling
  166. simultaneously
  167. skewed
  168. slightly
  169. small
  170. societies
  171. society
  172. spend
  173. sports
  174. stable
  175. successful
  176. suffer
  177. suggests
  178. surprise
  179. surprisingly
  180. tend
  181. theories
  182. thrown
  183. time
  184. today
  185. tool
  186. tools
  187. top
  188. twins
  189. wider
  190. womb
  191. word
  192. world
  193. worse
  194. write
  195. wrong
  196. years
  197. young