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A Workaholic Economy For the first century or so of the industrial revolution, increased productivity led to decreases in working hours. Employees who had been putting in 12-hour days, six days a week, found their time on the job shrinking to 10 hours daily, then, finally, to eight hours, five days a week. Only a generation ago social planners worried about what people would do with all this new-found free time. In the US, at least, it seems they need not have bothered. Although the output per hour of work has more than doubled since 1945, leisure seems reserved largely for the unemployed and underemployed. Those who work full-time spend as much time on the job as they did at the end of World War II. In fact, working hours have increased noticeably since 1970 - perhaps because real wages have stagnated since that year. Booksellers now abound with manuals describing how to manage time and cope with stress. There are several reasons for lost leisure. Since 1979, companies have responded to improvements in the business climate by having employees work overtime rather than hiring extra personnel, says economist Juliet B. Schor of Harvard University. Indeed, the current economic recovery has gained a certain amount of notoriety for its “jobless” nature: increased production has been almost entirely decoupled from employment. Some firms are even downsizing as their profits climb. “All things being equal, we’d be better off spreading around the work,” observes labour economist Ronald G. Ehrenberg of Cornell University. Yet a host of factors pushes employers to hire fewer workers for more hours and, at the same time, compels workers to spend more time on the job. Most of those incentives involve what Ehrenberg calls the structure of compensation: quirks in the way salaries and benefits are organized that make it more profitable to ask 40 employees to labour extra hour each than to hire one more worker to do the same 40-hour job. Professional and managerial employees supply the most obvious reason along these lines. Once people are on salaries they cost to a firm is the same whether they spend 35 hours a week in the office or 70. Diminishing returns may eventually set in as overworked employees lose efficiency or leave for more arable pastures. But in the short run, the employer’s incentive is clear. Even hourly employees receive benefits - such as pension contributions and medical insurance - that are not tied to the number of hours they work. Therefore, it is more profitable for employers to work their existing employees harder. For all that employees complain about long hours, they, they, too, have reasons not to trade money for leisure. “People who work reduced hours pay a huge penalty in career terms,” Schor maintains. “It’s taken as a negative signal” about their commitment to the firms” [Lotte] Bailey [of Massachusetts Institute of Technology] adds that many corporate managers find it difficult to measure the contribution of their underlings to a firm’s well-being, so they use the number of hours worked as a proxy for output. “Employees know this,” she says, and they adjust their behavior accordingly. “Although the image of the good worker is the one whose life belongs to the company,”Bailey says, “it doesn’t fit the facts.” She cites both quantitative and qualitative studies that show increased productivity for part-time workers: they make better use of the time they have, and they are less likely to succumb to fatigue in stressful jobs. Companies that employ more workers for less time also gain from the resulting redundancy, she asserts. “The extra people can cover the contingencies that you know are going to happen, such as when crises take people away from the workplace.” Positive experiences with reduced hours have begun to change the more-is-better culture at some companies, Schor reports. Larger firms, in particular, appear to be more willing to experiment with flexible working arrangements...

It may take even more than changes in the financial and cultural structures of employment for workers successfully to trade increased productivity and money for leisure time, Schor contends. She says the U.S. market for goods has become skewed by the assumption of full-time, two-career households. Automobile makers no longer manufacture cheap models, and developers do not build the tiny bungalows that served the first postwar generation of home buyers. Not even the humblest household object is made without a microprocessor. As Schor notes, the situation is a grima inversion of the “appropriate technology” vision that designers have had for developing countries: U.S. goods are appropriate only for high incomes and long hours.

（含图）

A Workaholic Economy For the first century or so of the industrial revolution, increased productivity led to decreases in working hours. Employees who had been putting in 12-hour days, six days a week, found their time on the job shrinking to 10 hours daily, then, finally, to eight hours, five days a week. Only a generation ago social planners worried about what people would do with all this new-found free time. In the US, at least, it seems they need not have bothered. Although the output per hour of work has more than doubled since 1945, leisure seems reserved largely for the unemployed and underemployed. Those who work full-time spend as much time on the job as they did at the end of World War II. In fact, working hours have increased noticeably since 1970 - perhaps because real wages have stagnated since that year. Booksellers now abound with manuals describing how to manage time and cope with stress. There are several reasons for lost leisure. Since 1979, companies have responded to improvements in the business climate by having employees work overtime rather than hiring extra personnel, says economist Juliet B. Schor of Harvard University. Indeed, the current economic recovery has gained a certain amount of notoriety for its “jobless” nature: increased production has been almost entirely decoupled from employment. Some firms are even downsizing as their profits climb. “All things being equal, we’d be better off spreading around the work,” observes labour economist Ronald G. Ehrenberg of Cornell University. Yet a host of factors pushes employers to hire fewer workers for more hours and, at the same time, compels workers to spend more time on the job. Most of those incentives involve what Ehrenberg calls the structure of compensation: quirks in the way salaries and benefits are organized that make it more profitable to ask 40 employees to labour extra hour each than to hire one more worker to do the same 40-hour job. Professional and managerial employees supply the most obvious reason along these lines. Once people are on salaries they cost to a firm is the same whether they spend 35 hours a week in the office or 70. Diminishing returns may eventually set in as overworked employees lose efficiency or leave for more arable pastures. But in the short run, the employer’s incentive is clear. Even hourly employees receive benefits - such as pension contributions and medical insurance - that are not tied to the number of hours they work. Therefore, it is more profitable for employers to work their existing employees harder. For all that employees complain about long hours, they, they, too, have reasons not to trade money for leisure. “People who work reduced hours pay a huge penalty in career terms,” Schor maintains. “It’s taken as a negative signal” about their commitment to the firms” [Lotte] Bailey [of Massachusetts Institute of Technology] adds that many corporate managers find it difficult to measure the contribution of their underlings to a firm’s well-being, so they use the number of hours worked as a proxy for output. “Employees know this,” she says, and they adjust their behavior accordingly. “Although the image of the good worker is the one whose life belongs to the company,”Bailey says, “it doesn’t fit the facts.” She cites both quantitative and qualitative studies that show increased productivity for part-time workers: they make better use of the time they have, and they are less likely to succumb to fatigue in stressful jobs. Companies that employ more workers for less time also gain from the resulting redundancy, she asserts. “The extra people can cover the contingencies that you know are going to happen, such as when crises take people away from the workplace.” Positive experiences with reduced hours have begun to change the more-is-better culture at some companies, Schor reports. Larger firms, in particular, appear to be more willing to experiment with flexible working arrangements...

It may take even more than changes in the financial and cultural structures of employment for workers successfully to trade increased productivity and money for leisure time, Schor contends. She says the U.S. market for goods has become skewed by the assumption of full-time, two-career households. Automobile makers no longer manufacture cheap models, and developers do not build the tiny bungalows that served the first postwar generation of home buyers. Not even the humblest household object is made without a microprocessor. As Schor notes, the situation is a grima inversion of the “appropriate technology” vision that designers have had for developing countries: U.S. goods are appropriate only for high incomes and long hours.

（含图）

A Workaholic Economy For the first century or so of the industrial revolution, increased productivity led to decreases in working hours. Employees who had been putting in 12-hour days, six days a week, found their time on the job shrinking to 10 hours daily, then, finally, to eight hours, five days a week. Only a generation ago social planners worried about what people would do with all this new-found free time. In the US, at least, it seems they need not have bothered. Although the output per hour of work has more than doubled since 1945, leisure seems reserved largely for the unemployed and underemployed. Those who work full-time spend as much time on the job as they did at the end of World War II. In fact, working hours have increased noticeably since 1970 - perhaps because real wages have stagnated since that year. Booksellers now abound with manuals describing how to manage time and cope with stress. There are several reasons for lost leisure. Since 1979, companies have responded to improvements in the business climate by having employees work overtime rather than hiring extra personnel, says economist Juliet B. Schor of Harvard University. Indeed, the current economic recovery has gained a certain amount of notoriety for its “jobless” nature: increased production has been almost entirely decoupled from employment. Some firms are even downsizing as their profits climb. “All things being equal, we’d be better off spreading around the work,” observes labour economist Ronald G. Ehrenberg of Cornell University. Yet a host of factors pushes employers to hire fewer workers for more hours and, at the same time, compels workers to spend more time on the job. Most of those incentives involve what Ehrenberg calls the structure of compensation: quirks in the way salaries and benefits are organized that make it more profitable to ask 40 employees to labour extra hour each than to hire one more worker to do the same 40-hour job. Professional and managerial employees supply the most obvious reason along these lines. Once people are on salaries they cost to a firm is the same whether they spend 35 hours a week in the office or 70. Diminishing returns may eventually set in as overworked employees lose efficiency or leave for more arable pastures. But in the short run, the employer’s incentive is clear. Even hourly employees receive benefits - such as pension contributions and medical insurance - that are not tied to the number of hours they work. Therefore, it is more profitable for employers to work their existing employees harder. For all that employees complain about long hours, they, they, too, have reasons not to trade money for leisure. “People who work reduced hours pay a huge penalty in career terms,” Schor maintains. “It’s taken as a negative signal” about their commitment to the firms” [Lotte] Bailey [of Massachusetts Institute of Technology] adds that many corporate managers find it difficult to measure the contribution of their underlings to a firm’s well-being, so they use the number of hours worked as a proxy for output. “Employees know this,” she says, and they adjust their behavior accordingly. “Although the image of the good worker is the one whose life belongs to the company,”Bailey says, “it doesn’t fit the facts.” She cites both quantitative and qualitative studies that show increased productivity for part-time workers: they make better use of the time they have, and they are less likely to succumb to fatigue in stressful jobs. Companies that employ more workers for less time also gain from the resulting redundancy, she asserts. “The extra people can cover the contingencies that you know are going to happen, such as when crises take people away from the workplace.” Positive experiences with reduced hours have begun to change the more-is-better culture at some companies, Schor reports. Larger firms, in particular, appear to be more willing to experiment with flexible working arrangements...

It may take even more than changes in the financial and cultural structures of employment for workers successfully to trade increased productivity and money for leisure time, Schor contends. She says the U.S. market for goods has become skewed by the assumption of full-time, two-career households. Automobile makers no longer manufacture cheap models, and developers do not build the tiny bungalows that served the first postwar generation of home buyers. Not even the humblest household object is made without a microprocessor. As Schor notes, the situation is a grima inversion of the “appropriate technology” vision that designers have had for developing countries: U.S. goods are appropriate only for high incomes and long hours.

（含图）

A Workaholic Economy For the first century or so of the industrial revolution, increased productivity led to decreases in working hours. Employees who had been putting in 12-hour days, six days a week, found their time on the job shrinking to 10 hours daily, then, finally, to eight hours, five days a week. Only a generation ago social planners worried about what people would do with all this new-found free time. In the US, at least, it seems they need not have bothered. Although the output per hour of work has more than doubled since 1945, leisure seems reserved largely for the unemployed and underemployed. Those who work full-time spend as much time on the job as they did at the end of World War II. In fact, working hours have increased noticeably since 1970 - perhaps because real wages have stagnated since that year. Booksellers now abound with manuals describing how to manage time and cope with stress. There are several reasons for lost leisure. Since 1979, companies have responded to improvements in the business climate by having employees work overtime rather than hiring extra personnel, says economist Juliet B. Schor of Harvard University. Indeed, the current economic recovery has gained a certain amount of notoriety for its “jobless” nature: increased production has been almost entirely decoupled from employment. Some firms are even downsizing as their profits climb. “All things being equal, we’d be better off spreading around the work,” observes labour economist Ronald G. Ehrenberg of Cornell University. Yet a host of factors pushes employers to hire fewer workers for more hours and, at the same time, compels workers to spend more time on the job. Most of those incentives involve what Ehrenberg calls the structure of compensation: quirks in the way salaries and benefits are organized that make it more profitable to ask 40 employees to labour extra hour each than to hire one more worker to do the same 40-hour job. Professional and managerial employees supply the most obvious reason along these lines. Once people are on salaries they cost to a firm is the same whether they spend 35 hours a week in the office or 70. Diminishing returns may eventually set in as overworked employees lose efficiency or leave for more arable pastures. But in the short run, the employer’s incentive is clear. Even hourly employees receive benefits - such as pension contributions and medical insurance - that are not tied to the number of hours they work. Therefore, it is more profitable for employers to work their existing employees harder. For all that employees complain about long hours, they, they, too, have reasons not to trade money for leisure. “People who work reduced hours pay a huge penalty in career terms,” Schor maintains. “It’s taken as a negative signal” about their commitment to the firms” [Lotte] Bailey [of Massachusetts Institute of Technology] adds that many corporate managers find it difficult to measure the contribution of their underlings to a firm’s well-being, so they use the number of hours worked as a proxy for output. “Employees know this,” she says, and they adjust their behavior accordingly. “Although the image of the good worker is the one whose life belongs to the company,”Bailey says, “it doesn’t fit the facts.” She cites both quantitative and qualitative studies that show increased productivity for part-time workers: they make better use of the time they have, and they are less likely to succumb to fatigue in stressful jobs. Companies that employ more workers for less time also gain from the resulting redundancy, she asserts. “The extra people can cover the contingencies that you know are going to happen, such as when crises take people away from the workplace.” Positive experiences with reduced hours have begun to change the more-is-better culture at some companies, Schor reports. Larger firms, in particular, appear to be more willing to experiment with flexible working arrangements...

It may take even more than changes in the financial and cultural structures of employment for workers successfully to trade increased productivity and money for leisure time, Schor contends. She says the U.S. market for goods has become skewed by the assumption of full-time, two-career households. Automobile makers no longer manufacture cheap models, and developers do not build the tiny bungalows that served the first postwar generation of home buyers. Not even the humblest household object is made without a microprocessor. As Schor notes, the situation is a grima inversion of the “appropriate technology” vision that designers have had for developing countries: U.S. goods are appropriate only for high incomes and long hours.

（含图）

A Workaholic Economy For the first century or so of the industrial revolution, increased productivity led to decreases in working hours. Employees who had been putting in 12-hour days, six days a week, found their time on the job shrinking to 10 hours daily, then, finally, to eight hours, five days a week. Only a generation ago social planners worried about what people would do with all this new-found free time. In the US, at least, it seems they need not have bothered. Although the output per hour of work has more than doubled since 1945, leisure seems reserved largely for the unemployed and underemployed. Those who work full-time spend as much time on the job as they did at the end of World War II. In fact, working hours have increased noticeably since 1970 - perhaps because real wages have stagnated since that year. Booksellers now abound with manuals describing how to manage time and cope with stress. There are several reasons for lost leisure. Since 1979, companies have responded to improvements in the business climate by having employees work overtime rather than hiring extra personnel, says economist Juliet B. Schor of Harvard University. Indeed, the current economic recovery has gained a certain amount of notoriety for its “jobless” nature: increased production has been almost entirely decoupled from employment. Some firms are even downsizing as their profits climb. “All things being equal, we’d be better off spreading around the work,” observes labour economist Ronald G. Ehrenberg of Cornell University. Yet a host of factors pushes employers to hire fewer workers for more hours and, at the same time, compels workers to spend more time on the job. Most of those incentives involve what Ehrenberg calls the structure of compensation: quirks in the way salaries and benefits are organized that make it more profitable to ask 40 employees to labour extra hour each than to hire one more worker to do the same 40-hour job. Professional and managerial employees supply the most obvious reason along these lines. Once people are on salaries they cost to a firm is the same whether they spend 35 hours a week in the office or 70. Diminishing returns may eventually set in as overworked employees lose efficiency or leave for more arable pastures. But in the short run, the employer’s incentive is clear. Even hourly employees receive benefits - such as pension contributions and medical insurance - that are not tied to the number of hours they work. Therefore, it is more profitable for employers to work their existing employees harder. For all that employees complain about long hours, they, they, too, have reasons not to trade money for leisure. “People who work reduced hours pay a huge penalty in career terms,” Schor maintains. “It’s taken as a negative signal” about their commitment to the firms” [Lotte] Bailey [of Massachusetts Institute of Technology] adds that many corporate managers find it difficult to measure the contribution of their underlings to a firm’s well-being, so they use the number of hours worked as a proxy for output. “Employees know this,” she says, and they adjust their behavior accordingly. “Although the image of the good worker is the one whose life belongs to the company,”Bailey says, “it doesn’t fit the facts.” She cites both quantitative and qualitative studies that show increased productivity for part-time workers: they make better use of the time they have, and they are less likely to succumb to fatigue in stressful jobs. Companies that employ more workers for less time also gain from the resulting redundancy, she asserts. “The extra people can cover the contingencies that you know are going to happen, such as when crises take people away from the workplace.” Positive experiences with reduced hours have begun to change the more-is-better culture at some companies, Schor reports. Larger firms, in particular, appear to be more willing to experiment with flexible working arrangements...

It may take even more than changes in the financial and cultural structures of employment for workers successfully to trade increased productivity and money for leisure time, Schor contends. She says the U.S. market for goods has become skewed by the assumption of full-time, two-career households. Automobile makers no longer manufacture cheap models, and developers do not build the tiny bungalows that served the first postwar generation of home buyers. Not even the humblest household object is made without a microprocessor. As Schor notes, the situation is a grima inversion of the “appropriate technology” vision that designers have had for developing countries: U.S. goods are appropriate only for high incomes and long hours.

（含图）

A Workaholic Economy For the first century or so of the industrial revolution, increased productivity led to decreases in working hours. Employees who had been putting in 12-hour days, six days a week, found their time on the job shrinking to 10 hours daily, then, finally, to eight hours, five days a week. Only a generation ago social planners worried about what people would do with all this new-found free time. In the US, at least, it seems they need not have bothered. Although the output per hour of work has more than doubled since 1945, leisure seems reserved largely for the unemployed and underemployed. Those who work full-time spend as much time on the job as they did at the end of World War II. In fact, working hours have increased noticeably since 1970 - perhaps because real wages have stagnated since that year. Booksellers now abound with manuals describing how to manage time and cope with stress. There are several reasons for lost leisure. Since 1979, companies have responded to improvements in the business climate by having employees work overtime rather than hiring extra personnel, says economist Juliet B. Schor of Harvard University. Indeed, the current economic recovery has gained a certain amount of notoriety for its “jobless” nature: increased production has been almost entirely decoupled from employment. Some firms are even downsizing as their profits climb. “All things being equal, we’d be better off spreading around the work,” observes labour economist Ronald G. Ehrenberg of Cornell University. Yet a host of factors pushes employers to hire fewer workers for more hours and, at the same time, compels workers to spend more time on the job. Most of those incentives involve what Ehrenberg calls the structure of compensation: quirks in the way salaries and benefits are organized that make it more profitable to ask 40 employees to labour extra hour each than to hire one more worker to do the same 40-hour job. Professional and managerial employees supply the most obvious reason along these lines. Once people are on salaries they cost to a firm is the same whether they spend 35 hours a week in the office or 70. Diminishing returns may eventually set in as overworked employees lose efficiency or leave for more arable pastures. But in the short run, the employer’s incentive is clear. Even hourly employees receive benefits - such as pension contributions and medical insurance - that are not tied to the number of hours they work. Therefore, it is more profitable for employers to work their existing employees harder. For all that employees complain about long hours, they, they, too, have reasons not to trade money for leisure. “People who work reduced hours pay a huge penalty in career terms,” Schor maintains. “It’s taken as a negative signal” about their commitment to the firms” [Lotte] Bailey [of Massachusetts Institute of Technology] adds that many corporate managers find it difficult to measure the contribution of their underlings to a firm’s well-being, so they use the number of hours worked as a proxy for output. “Employees know this,” she says, and they adjust their behavior accordingly. “Although the image of the good worker is the one whose life belongs to the company,”Bailey says, “it doesn’t fit the facts.” She cites both quantitative and qualitative studies that show increased productivity for part-time workers: they make better use of the time they have, and they are less likely to succumb to fatigue in stressful jobs. Companies that employ more workers for less time also gain from the resulting redundancy, she asserts. “The extra people can cover the contingencies that you know are going to happen, such as when crises take people away from the workplace.” Positive experiences with reduced hours have begun to change the more-is-better culture at some companies, Schor reports. Larger firms, in particular, appear to be more willing to experiment with flexible working arrangements...

It may take even more than changes in the financial and cultural structures of employment for workers successfully to trade increased productivity and money for leisure time, Schor contends. She says the U.S. market for goods has become skewed by the assumption of full-time, two-career households. Automobile makers no longer manufacture cheap models, and developers do not build the tiny bungalows that served the first postwar generation of home buyers. Not even the humblest household object is made without a microprocessor. As Schor notes, the situation is a grima inversion of the “appropriate technology” vision that designers have had for developing countries: U.S. goods are appropriate only for high incomes and long hours.

（含图）

A Workaholic Economy For the first century or so of the industrial revolution, increased productivity led to decreases in working hours. Employees who had been putting in 12-hour days, six days a week, found their time on the job shrinking to 10 hours daily, then, finally, to eight hours, five days a week. Only a generation ago social planners worried about what people would do with all this new-found free time. In the US, at least, it seems they need not have bothered. Although the output per hour of work has more than doubled since 1945, leisure seems reserved largely for the unemployed and underemployed. Those who work full-time spend as much time on the job as they did at the end of World War II. In fact, working hours have increased noticeably since 1970 - perhaps because real wages have stagnated since that year. Booksellers now abound with manuals describing how to manage time and cope with stress. There are several reasons for lost leisure. Since 1979, companies have responded to improvements in the business climate by having employees work overtime rather than hiring extra personnel, says economist Juliet B. Schor of Harvard University. Indeed, the current economic recovery has gained a certain amount of notoriety for its “jobless” nature: increased production has been almost entirely decoupled from employment. Some firms are even downsizing as their profits climb. “All things being equal, we’d be better off spreading around the work,” observes labour economist Ronald G. Ehrenberg of Cornell University. Yet a host of factors pushes employers to hire fewer workers for more hours and, at the same time, compels workers to spend more time on the job. Most of those incentives involve what Ehrenberg calls the structure of compensation: quirks in the way salaries and benefits are organized that make it more profitable to ask 40 employees to labour extra hour each than to hire one more worker to do the same 40-hour job. Professional and managerial employees supply the most obvious reason along these lines. Once people are on salaries they cost to a firm is the same whether they spend 35 hours a week in the office or 70. Diminishing returns may eventually set in as overworked employees lose efficiency or leave for more arable pastures. But in the short run, the employer’s incentive is clear. Even hourly employees receive benefits - such as pension contributions and medical insurance - that are not tied to the number of hours they work. Therefore, it is more profitable for employers to work their existing employees harder. For all that employees complain about long hours, they, they, too, have reasons not to trade money for leisure. “People who work reduced hours pay a huge penalty in career terms,” Schor maintains. “It’s taken as a negative signal” about their commitment to the firms” [Lotte] Bailey [of Massachusetts Institute of Technology] adds that many corporate managers find it difficult to measure the contribution of their underlings to a firm’s well-being, so they use the number of hours worked as a proxy for output. “Employees know this,” she says, and they adjust their behavior accordingly. “Although the image of the good worker is the one whose life belongs to the company,”Bailey says, “it doesn’t fit the facts.” She cites both quantitative and qualitative studies that show increased productivity for part-time workers: they make better use of the time they have, and they are less likely to succumb to fatigue in stressful jobs. Companies that employ more workers for less time also gain from the resulting redundancy, she asserts. “The extra people can cover the contingencies that you know are going to happen, such as when crises take people away from the workplace.” Positive experiences with reduced hours have begun to change the more-is-better culture at some companies, Schor reports. Larger firms, in particular, appear to be more willing to experiment with flexible working arrangements...

It may take even more than changes in the financial and cultural structures of employment for workers successfully to trade increased productivity and money for leisure time, Schor contends. She says the U.S. market for goods has become skewed by the assumption of full-time, two-career households. Automobile makers no longer manufacture cheap models, and developers do not build the tiny bungalows that served the first postwar generation of home buyers. Not even the humblest household object is made without a microprocessor. As Schor notes, the situation is a grima inversion of the “appropriate technology” vision that designers have had for developing countries: U.S. goods are appropriate only for high incomes and long hours.

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（含图）

Section 1

Study of the origins and distribution of human populations used to be based on archaeological and fossil evidence. A number of techniques developed since the 1950s, however, have placed the study of these subjects on a sounder and more objective footing. The best information on early population movements is now being obtained from the “archaeology of the living body”, the clues to be found in genetic material.

Section 2

Recent work on the problem of when people first entered the Americas is an example of the value of these new techniques. North-east Asia and Siberia have long been accepted as the launching ground for the first human colonisers of the New World. But was there one major wave of migration across the Bering Strait into the Americas, or several? And when did this event, or events, take place? In recent years, new clues have come from research into genetics, including the distribution of genetic markers in modern Native Americans.

Section 3

An important project, led by the biological anthropologist Robert Williams, focused on the variants (called Gm alleles) of one particular protein - immunoglobin G - found in the fluid portion of human blood. All proteins “drift”, or produce variants, over the generations, and members of an interbreeding human population will share a set of such variants. Thus, comparing the Gm alleles of two different populations (e.g. two Indian tribes), one can establish their genetic “distance”, which itself can be calibrated to give an indication of the length of time since these populations last interbred.

Section 4

Williams and his colleagues sampled the blood of over 5,000 American Indians in western North America during a twenty-year period. They found that their Gm alleles could be divided into two groups, one of which also corresponded to the genetic typing of Central and South American Indians. Other tests showed that the Inuit (or Eskimo) and Aleut formed a third group. From this evidence it was deduced that there had been three major waves of migration across the Bering Strait. The first, Paleo-Indian, wave more than 15,000 years ago was ancestral to all Central and South American Indians. The second wave, about 14,000 - 12,000 years ago, brought Na-Dene hunters, ancestors of the Navajo and Apache (who only migrated south from Canada about 600 or 700 years ago). The third wave, perhaps 10,000 or 9,000 years ago, saw the migration from North-east Asia of groups ancestral to the modern Eskimo and Aleut.

Section 5

How far does other research support these conclusions? Geneticist Douglas Wallace has studied mitochondrial DNA in blood samples from three widely separated Native American groups: Pima-Pago Indians in Arizona, Maya Indians on the Yucatan peninsula, Mexico, and Ticuna Indians in the Upper Amazon region of Brazil. As would have been predicted by Robert Williams’s work, all three groups appear to be descended from the same ancestral (Paleo-Indian) population.

Section 6

There are two other kinds of research that have thrown some light on the origins of the Native American population; they involve the study of teeth and of languages. The biological anthropologist Christy Turner is an expert in the analysis of changing physical characteristics in human teeth. He argues that tooth crowns and roots have a high genetic component, minimally affected by environmental and other factors. Studies carried out by Turner of many thousands of New and Old World specimens, both ancient and modern, suggest that the majority of prehistoric Americans are linked to Northern Asian populations by crown and root traits such as incisor shoveling (a scooping out on one or both surfaces of the tooth), single-rooted upper first premolars and triple-rooted lower first molars. According to Turner, this ties in with the idea of a single Paleo-Indian migration out of North Asia, which he sets at before 14,000 years ago by calibrating rates of dental micro-evolution. Tooth analyses also suggest that there were two later migrations of Na-Denes and Eskimo-Aleut.

以下是从图片中提取和整理的文本：

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**Population movements and genetics**

1. Study of the origins and distribution of human populations used to be based on archaeological and fossil evidence. A number of techniques developed since the 1950s, however, have placed the study of these subjects on a sounder and more objective footing. The best information on early population movements is now being obtained from the “archaeology of the living body”, the clues to be found in genetic material.

2. Recent work on the problem of when people first entered the Americas is an example of the value of these new techniques. North-east Asia and Siberia have long been accepted as the launching ground for the first human colonisers of the New World. But was there one major wave of migration across the Bering Strait into the Americas, or several? And when did this event, or events, take place? In recent years, new clues have come from research into genetics, including the distribution of genetic markers in modern Native Americans.

3. An important project, led by the biological anthropologist Robert Williams, focused on the variants (called Gm alleles) of one particular protein - immunoglobin G - found in the fluid portion of human blood. All proteins “drift”, or produce variants, over the generations, and members of an interbreeding human population will share a set of such variants. Thus, comparing the Gm alleles of two different populations (e.g. two Indian tribes), one can establish their genetic “distance”, which itself can be calibrated to give an indication of the length of time since these populations last interbred.

4. Williams and his colleagues sampled the blood of over 5,000 American Indians in western North America during a twenty-year period. They found that their Gm alleles could be divided into two groups, one of which also corresponded to the genetic typing of Central and South American Indians. Other tests showed that the Inuit (or Eskimo) and Aleut formed a third group. From this evidence it was deduced that there had been three major waves of migration across the Bering Strait. The first, Paleo-Indian, wave more than 15,000 years ago was ancestral to all Central and South American Indians. The second wave, about 14,000 - 12,000 years ago, brought Na-Dene hunters, ancestors of the Navajo and Apache (who only migrated south from Canada about 600 or 700 years ago). The third wave, perhaps 10,000 or 9,000 years ago, saw the migration from North-east Asia of groups ancestral to the modern Eskimo and Aleut.

5. How far does other research support these conclusions? Geneticist Douglas Wallace has studied mitochondrial DNA in blood samples from three widely separated Native American groups: Pima-Pago Indians in Arizona, Maya Indians on the Yucatan peninsula, Mexico, and Ticuna Indians in the Upper Amazon region of Brazil. As would have been predicted by Robert Williams’s work, all three groups appear to be descended from the same ancestral (Paleo-Indian) population.

6. There are two other kinds of research that have thrown some light on the origins of the Native American population; they involve the study of teeth and of languages. The biological anthropologist Christy Turner is an expert in the analysis of changing physical characteristics in human teeth. He argues that tooth crowns and roots have a high genetic component, minimally affected by environmental and other factors. Studies carried out by Turner of many thousands of New and Old World specimens, both ancient and modern, suggest that the majority of prehistoric Americans are linked to Northern Asian populations by crown and root traits such as incisor shoveling (a scooping out on one or both surfaces of the tooth), single-rooted upper first premolars and triple-rooted lower first molars. According to Turner, this ties in with the idea of a single Paleo-Indian migration out of North Asia, which he sets at before 14,000 years ago by calibrating rates of dental micro-evolution. Tooth analyses also suggest that there were two later migrations of Na-Denes and Eskimo-Aleut.

7. The linguist Joseph Greenberg has, since the 1950s, argued that all Native American languages belong to a single “Amerind” family, except for Na-Dene and Eskimo-Aleut - a view that gives credence to the idea of three main migrations. Greenberg is in a minority among fellow linguists, most of whom favour the notion of a great many waves of migration to account for the more than 1,000 languages spoken at one time by American Indians. But there is no doubt that the new genetic and dental evidence provides strong backing for Greenberg’s view. Dates given for the migrations should nevertheless be treated with caution, except where supported by hard archaeological evidence.

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以下是从图片中提取和整理的文本：

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**Population movements and genetics**

1. Study of the origins and distribution of human populations used to be based on archaeological and fossil evidence. A number of techniques developed since the 1950s, however, have placed the study of these subjects on a sounder and more objective footing. The best information on early population movements is now being obtained from the “archaeology of the living body”, the clues to be found in genetic material.

2. Recent work on the problem of when people first entered the Americas is an example of the value of these new techniques. North-east Asia and Siberia have long been accepted as the launching ground for the first human colonisers of the New World. But was there one major wave of migration across the Bering Strait into the Americas, or several? And when did this event, or events, take place? In recent years, new clues have come from research into genetics, including the distribution of genetic markers in modern Native Americans.

3. An important project, led by the biological anthropologist Robert Williams, focused on the variants (called Gm alleles) of one particular protein - immunoglobin G - found in the fluid portion of human blood. All proteins “drift”, or produce variants, over the generations, and members of an interbreeding human population will share a set of such variants. Thus, comparing the Gm alleles of two different populations (e.g. two Indian tribes), one can establish their genetic “distance”, which itself can be calibrated to give an indication of the length of time since these populations last interbred.

4. Williams and his colleagues sampled the blood of over 5,000 American Indians in western North America during a twenty-year period. They found that their Gm alleles could be divided into two groups, one of which also corresponded to the genetic typing of Central and South American Indians. Other tests showed that the Inuit (or Eskimo) and Aleut formed a third group. From this evidence it was deduced that there had been three major waves of migration across the Bering Strait. The first, Paleo-Indian, wave more than 15,000 years ago was ancestral to all Central and South American Indians. The second wave, about 14,000 - 12,000 years ago, brought Na-Dene hunters, ancestors of the Navajo and Apache (who only migrated south from Canada about 600 or 700 years ago). The third wave, perhaps 10,000 or 9,000 years ago, saw the migration from North-east Asia of groups ancestral to the modern Eskimo and Aleut.

5. How far does other research support these conclusions? Geneticist Douglas Wallace has studied mitochondrial DNA in blood samples from three widely separated Native American groups: Pima-Pago Indians in Arizona, Maya Indians on the Yucatan peninsula, Mexico, and Ticuna Indians in the Upper Amazon region of Brazil. As would have been predicted by Robert Williams’s work, all three groups appear to be descended from the same ancestral (Paleo-Indian) population.

6. There are two other kinds of research that have thrown some light on the origins of the Native American population; they involve the study of teeth and of languages. The biological anthropologist Christy Turner is an expert in the analysis of changing physical characteristics in human teeth. He argues that tooth crowns and roots have a high genetic component, minimally affected by environmental and other factors. Studies carried out by Turner of many thousands of New and Old World specimens, both ancient and modern, suggest that the majority of prehistoric Americans are linked to Northern Asian populations by crown and root traits such as incisor shoveling (a scooping out on one or both surfaces of the tooth), single-rooted upper first premolars and triple-rooted lower first molars. According to Turner, this ties in with the idea of a single Paleo-Indian migration out of North Asia, which he sets at before 14,000 years ago by calibrating rates of dental micro-evolution. Tooth analyses also suggest that there were two later migrations of Na-Denes and Eskimo-Aleut.

7. The linguist Joseph Greenberg has, since the 1950s, argued that all Native American languages belong to a single “Amerind” family, except for Na-Dene and Eskimo-Aleut - a view that gives credence to the idea of three main migrations. Greenberg is in a minority among fellow linguists, most of whom favour the notion of a great many waves of migration to account for the more than 1,000 languages spoken at one time by American Indians. But there is no doubt that the new genetic and dental evidence provides strong backing for Greenberg’s view. Dates given for the migrations should nevertheless be treated with caution, except where supported by hard archaeological evidence.

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**Population movements and genetics**

1. Study of the origins and distribution of human populations used to be based on archaeological and fossil evidence. A number of techniques developed since the 1950s, however, have placed the study of these subjects on a sounder and more objective footing. The best information on early population movements is now being obtained from the “archaeology of the living body”, the clues to be found in genetic material.

2. Recent work on the problem of when people first entered the Americas is an example of the value of these new techniques. North-east Asia and Siberia have long been accepted as the launching ground for the first human colonisers of the New World. But was there one major wave of migration across the Bering Strait into the Americas, or several? And when did this event, or events, take place? In recent years, new clues have come from research into genetics, including the distribution of genetic markers in modern Native Americans.

3. An important project, led by the biological anthropologist Robert Williams, focused on the variants (called Gm alleles) of one particular protein - immunoglobin G - found in the fluid portion of human blood. All proteins “drift”, or produce variants, over the generations, and members of an interbreeding human population will share a set of such variants. Thus, comparing the Gm alleles of two different populations (e.g. two Indian tribes), one can establish their genetic “distance”, which itself can be calibrated to give an indication of the length of time since these populations last interbred.

4. Williams and his colleagues sampled the blood of over 5,000 American Indians in western North America during a twenty-year period. They found that their Gm alleles could be divided into two groups, one of which also corresponded to the genetic typing of Central and South American Indians. Other tests showed that the Inuit (or Eskimo) and Aleut formed a third group. From this evidence it was deduced that there had been three major waves of migration across the Bering Strait. The first, Paleo-Indian, wave more than 15,000 years ago was ancestral to all Central and South American Indians. The second wave, about 14,000 - 12,000 years ago, brought Na-Dene hunters, ancestors of the Navajo and Apache (who only migrated south from Canada about 600 or 700 years ago). The third wave, perhaps 10,000 or 9,000 years ago, saw the migration from North-east Asia of groups ancestral to the modern Eskimo and Aleut.

5. How far does other research support these conclusions? Geneticist Douglas Wallace has studied mitochondrial DNA in blood samples from three widely separated Native American groups: Pima-Pago Indians in Arizona, Maya Indians on the Yucatan peninsula, Mexico, and Ticuna Indians in the Upper Amazon region of Brazil. As would have been predicted by Robert Williams’s work, all three groups appear to be descended from the same ancestral (Paleo-Indian) population.

6. There are two other kinds of research that have thrown some light on the origins of the Native American population; they involve the study of teeth and of languages. The biological anthropologist Christy Turner is an expert in the analysis of changing physical characteristics in human teeth. He argues that tooth crowns and roots have a high genetic component, minimally affected by environmental and other factors. Studies carried out by Turner of many thousands of New and Old World specimens, both ancient and modern, suggest that the majority of prehistoric Americans are linked to Northern Asian populations by crown and root traits such as incisor shoveling (a scooping out on one or both surfaces of the tooth), single-rooted upper first premolars and triple-rooted lower first molars. According to Turner, this ties in with the idea of a single Paleo-Indian migration out of North Asia, which he sets at before 14,000 years ago by calibrating rates of dental micro-evolution. Tooth analyses also suggest that there were two later migrations of Na-Denes and Eskimo-Aleut.

7. The linguist Joseph Greenberg has, since the 1950s, argued that all Native American languages belong to a single “Amerind” family, except for Na-Dene and Eskimo-Aleut - a view that gives credence to the idea of three main migrations. Greenberg is in a minority among fellow linguists, most of whom favour the notion of a great many waves of migration to account for the more than 1,000 languages spoken at one time by American Indians. But there is no doubt that the new genetic and dental evidence provides strong backing for Greenberg’s view. Dates given for the migrations should nevertheless be treated with caution, except where supported by hard archaeological evidence.

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