In the first decade of the 21st century, only people with postgraduate degrees experienced an increase in earnings.What If Middle-Class Jobs Disappear?F. The introduction of the tractor and improvements in the factory rapidly reduced the demand for uneducated workers. By the 1930s, a marginal farm hand could not produce enough to justify his employment. Sharecropping, never much better than a subsistence occupation, was no longer viable(可行的). Meanwhile, machines were replacing manufacturing occupations like cigar rolling and glass blowing for light bulbs.G. The structural-transition interpretation of the unemployment problem of the 1930s would be that the demand for uneducated workers in the United States had fallen, but the supply remained high. The high school graduation rate was only 8.8% in 1912 and still just 29% in 1931. By 1950, it had reached 59%. With a new generation of workers who had completed high school, the mismatch between skills and jobs had been greatly reduced.H. What took place after World War Ⅱ was not the revival of a 1920s economy, with its small farming units, urban manufacturing, and plurality of laborers. Instead, the 1950s saw the creation of a new suburban economy, with a plurality of white-collar workers. With an expanded transportation and communications infrastructure(基础设施), businesses needed telephone operators, shipping clerks and similar occupations. If you could read, follow simple instructions, and settle into a routine, you could find a job in the post-war economy.I. The trend away from manual labor has continued. Even within the manufacturing sector, the share of production and non-supervisory workers in manufacturing employment went from over 85% just after World War II to less than 70% in more recent years. To put this another way, the proportion of white-collar work in manufacturing has doubled over the past 50 years. On the factory floor itself, work has become less physically demanding. Instead, it requires more cognitive skills and the ability to understand and carry out well-defined procedures.J. As noted earlier, the proportion of clerical workers in the economy peaked in 1980. By that date, computers and advanced communications equipment had already begun to affect telephone operations and banking. The rise of the personal computer and the Internet has widened the impact of these technologies to include nearly every business and industry.K. The economy today differs from that of a generation ago. Mortgage and consumer loan underwriters(风险评估人) have been replaced by credit scoring. Record stores have been replaced by music downloads. Book stores are closing, while sales of books on electronic readers have increased. Data entry has been moved off shore. Routine customer support also has been outsourced(外包) overseas.L. These trends serve to limit the availability of well-defined jobs. If a job can be characterized by a precise set of instructions, then that job is a candidate to be automated or outsourced to modestly educated workers in developing countries. The result is what David Autor calls the polarization of the American job market.M. Using the latest Census Bureau data, Matthew Slaughter found that from 2000 to 2010 the real earnings of college graduates (with no advanced degree) fell by more in percentage terms than the earnings of high school graduates. In fact, over this period the only education category to show an increase in earnings was those with advanced degrees.N. The outlook for mid-skill jobs would not appear to be bright. Communications technology and computer intelligence continue to improve, putting more occupations at risk. For example, many people earn a living as drivers, including trucks and taxicabs. However, the age of driver less vehicles appears to be moving closer. Another example is in the field of education. In the fall of 2011, an experiment with an online course in artificial intelligence conducted by two Stanford professors drew tens of thousands of registrants(报名者).This increases the student-teacher ratio by a factor of close to a thousand. Imagine the number of teaching jobs that might be eliminated if this could be done for math, economics, chemistry, and so on.O. It's important to bear in mind that when we offer a structural interpretation of unemployment, a "loss of jobs" means an increase in productivity. Traditionally, economists have argued that productivity increases are a good thing, even though they may cause unemployment for some workers in the short run. In the long run, the economy does not run out of jobs. Rather, new jobs emerge as old jobs disappear. The story we tell is that average well-being rises, and the more people are able to adapt, the more widespread the improvement becomes.A、A. The most recent recession in the United States began in December of 2007 and ended in June 2009, according to the National Bureau of Economic Research. However, two years after the official end of the recession, few Americans would say that economic troubles are behind us. The unemployment rate, in particular, remains above 9%. Some labor market indicators, such as the proportion of long-term unemployed, are worse now than for any postwar recession.B、B. There are two widely circulated narratives to explain what's going on. The Keynesian narrative is that there has been a major drop in aggregate demand. According to this narrative, the slump can be largely cured by using monetary and fiscal(财政的) stimulus. The main anti-Keynesian narrative is that businesses are suffering from uncertainty and over-regulation. According to this narrative, the slump can be cured by having the government commit to and follow a more hands-off approach.C、C. I want to suggest a third interpretation. Without ruling out a role for aggregate demand or for the regulatory environment, I wish to suggest that structural change is an important factor in the current rate of high unemployment. The economy is in a state of transition, in which the middle-class jobs that emerged after World War Ⅱ have begun to decline. As Erik Brynjolfsson and Andrew McAfee put it in a recent e-book Race Against the Machine:"The root of our problems is not that we're in a great recession, or a great stagnation(停滞), but rather that we are in the early throes(阵痛) of a great restructuring."D、D. In fact, I believe the Great Depression of the 1930s can also be interpreted in part as an economic transition. The impact of the internal combustion engine(内燃机) and the small electric motor on farming and manufacturing reduced the value of uneducated laborers. Instead, by the 1950s, a middle class of largely clerical(从事文秘工作的) workers was the most significant part of the labor force. Between 1930 and 1950, the United States economy underwent a great transition. Demand fell for human effort such as lifting, squeezing, and hammering. Demand increased for workers who could read and follow directions. The evolutionary process eventually changed us from a nation of laborers to a nation of clerks.E、E. The proportion of employment classified as "clerical workers" grew from 5.2% in 1910 to a peak of 19.3% in 1980. (However, by 2000 this proportion had edged down to 17.4%.) Overall, workers classified as clerical workers, technical workers, managers and officials exceeded 50% of the labor force by 2000. Corresponding declines took place in the manual occupations. Workers classified as laborers, other than farm hands or miners, peaked at 11.4% of the labor force in 1920 but were barely 6% by 1950 and less than 4% by 2000. Farmers and farm laborers fell from 33% of the labor force in 1910 to less than 15% by 1950 and only 1.2% in 2000.