TedTest

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 witre or eat with their right hand. And in many parts of the world, it's still common practice to force ciedlhrn 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 shwiong the associated dfnreecfeis in arm length and bone density, and some ancient tools and arctiatfs showing evidence of left-hand use. And despite what many may think, handedness is not a choice. It can be predicted even before birth besad 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 domiannt 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 lteifes, and maintained it over the course of millennia. And while there have been several theories attempting to explain why hndndseeas exists in the first place, or why most people are right-handed, a recent mathematical model sgeugtss that the aautcl rtaio rtelecfs a balance between competitive and cooperative pressures on human evolution. The benefits of being left-handed are clearest in activities involving an opponent, like cambot 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 mnrioity to begin with, both right-handed and left-handed cireoottpms 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 opnneopt, 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 aaadgntve tend to grow until that advantage disappears. If ppoele were only fniihgtg and competing throughout human eluovtoin, nrautal seectloin 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 huamn 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 denped on the opponent, only 4% of top pyrales are left-handed, an example of the wider phenomenon of tool sharing. Just as young potential golfers can more easliy 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 sfuccusesl in a purely cooperative world, eventually disappearing from the population. So by correctly ptdcnreiig 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 smlal but stable minority reflects an equilibrium that comes from cmoivtiptee 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 lreagr pnrgtaecee of lefties in competitive hunter-gatherer societies, we may even find that the anrswes 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 _____ or eat with their right hand. And in many parts of the world, it's still common practice to force ________ 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 _______ the associated ___________ in arm length and bone density, and some ancient tools and _________ showing evidence of left-hand use. And despite what many may think, handedness is not a choice. It can be predicted even before birth _____ 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 ________ 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 _______, and maintained it over the course of millennia. And while there have been several theories attempting to explain why __________ exists in the first place, or why most people are right-handed, a recent mathematical model ________ that the ______ _____ ________ 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 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 ________ to begin with, both right-handed and left-handed ___________ 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 ________, 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 _________ tend to grow until that advantage disappears. If ______ were only ________ and competing throughout human _________, _______ _________ 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 _____ 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 ______ on the opponent, only 4% of top _______ are left-handed, an example of the wider phenomenon of tool sharing. Just as young potential golfers can more ______ 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 __________ 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 persistence of lefties as a _____ but stable minority reflects an equilibrium that comes from ___________ 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 ______ __________ of lefties in competitive hunter-gatherer societies, we may even find that the _______ to some puzzles of early human evolution are already in our hands.

Solution

players
showing
natural
larger
opponent
small
lefties
people
differences
advantage
successful
human
reflects
evolution
answers
write
competitive
fighting
artifacts
competitors
based
percentage
easily
minority
predicting
selection
ratio
dominant
combat
handedness
actual
children
suggests
depend

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

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