Despite the fact that we are a nation of immigrants -- or perhaps because of it -- immigration continues to be one of America's most contentious topics. The new law in Arizona authorizing police to arrest individuals who cannot show documents proving that they are in the country legally has set off a fresh bout of acrimony. But as in the past, much of the debate is founded on mythology.

1. Immigrants take jobs from American workers.

Although immigrants account for 12.5 percent of the U.S. population, they make up about 15 percent of the workforce. They are overrepresented among workers largely because the rest of our population is aging: Immigrants and their children have accounted for 58 percent of U.S. population growth since 1980. This probably won't change anytime soon. Low U.S. fertility rates and the upcoming retirement of the baby boomers mean that immigration is likely to be the only source of growth in what we call the "prime age" workforce -- workers ages 25 to 55 -- in the decades ahead. As record numbers of retirees begin drawing Social Security checks, younger immigrant workers will be paying taxes, somewhat easing the financial pressures on the system.

Moreover, immigrants tend to be concentrated in high- and low-skilled occupations that complement -- rather than compete with -- jobs held by native workers. And the foreign-born workers who fill lower-paying jobs are typically first-hired/first-fired employees, allowing employers to expand and contract their workforces rapidly. As a result, immigrants experience higher employment than natives during booms -- but they suffer higher job losses during downturns, including the current one.

It's true that an influx of new workers pushes wages down, but immigration also stimulates growth by creating new consumers, entrepreneurs and investors. As a result of this growth, economists estimate that wages for the vast majority of American workers are slightly higher than they would be without immigration. U.S. workers without a high school degree experience wage declines as a result of competition from immigrants, but these losses are modest, at just over 1 percent. Economists also estimate that for each job an immigrant fills, an additional job is created.

2. Immigration is at an all-time high, and most new immigrants came illegally.

The historic high came more than a century ago, in 1890, when immigrants made up 14.8 percent of our population. Today, about two-thirds of immigrants are here legally, either as naturalized citizens or as lawful permanent residents, more commonly known as "green card" holders. And of the approximately 10.8 million immigrants who are in the country illegally, about 40 percent arrived legally but overstayed their visas.

It's worth noting that although the unauthorized immigrant population includes more people from Mexico than from any other country, Mexicans are also the largest group of lawful immigrants. As for the flow of illegal immigrants, apprehensions along the U.S.-Mexico border have declined by more than 50 percent over the past four years, while increases in the size of the illegal population, which had been growing by about 500,000 a year for more than a decade, have stopped. This decline is largely due to the recession, but stepped-up border enforcement is playing a part.

3. Today's immigrants are not integrating into American life like past waves did.

The integration of immigrants remains a hallmark of America's vitality as a society and a source of admiration abroad, as it has been throughout our history. Although some people complain that today's immigrants are not integrating into U.S. society as quickly as previous newcomers did, the same charge was leveled at virtually every past wave of immigrants, including the large numbers of Germans, Irish and Italians who arrived in the 19th and early 20th centuries.

Today, as before, immigrant integration takes a generation or two. Learning English is one key driver of this process; the education and upward mobility of immigrants' children is the other. On the first count, today's immigrants consistently seek English instruction in such large numbers that adult-education programs cannot meet the demand, especially in places such as California. On the second count, the No Child Left Behind Act has played a critical role in helping educate immigrant children because it holds schools newly accountable for teaching them English.

However, the unauthorized status of millions of foreign-born immigrants can slow integration in crucial ways. For example, illegal immigrants are ineligible for in-state tuition at most public colleges and universities, putting higher education effectively out of their reach. And laws prohibiting unauthorized immigrants from getting driver's licenses or various professional credentials can leave them stuck in jobs with a high density of other immigrants and unable to advance.

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