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When President Lyndon B. Johnson signed the Immigration and Nationality Act of 1965 into law, the change ended a quota system that prioritized European immigration and helped to usher in an era of heavy inflows from Latin America and Asia.

As a result, America has a larger, more diverse population, and immigrants' children will serve as an increasingly important source of labor as native-born Baby Boomers age and begin to retire.

"It doesn't fix the demography of an aging society, it does change things," said Jeffrey Passel, a senior demographer at Pew Research Center in Washington and the author of a new report on how immigration since the 1960's has affected America's population. "It makes a difference in the growth in the labor force."

Check out the charts below from Pew to see how.

Here's how 1965 changed inflows

The graphic below shows just how big of an impact the 1965 law had on immigration. Before the law's inception, Ireland, Germany and the United Kingdom were entitled to 70 percent of U.S. visas and weren't using their full share. By changing the rules so other countries got more visas and family immigration gained priority, the U.S. better aligned supply and demand, Passel said.

New entrants are younger

Immigrants tend to be older than your typical American, and in 1960 were 57 years old on median — about twice the U.S.-born median age of 27. After the change, an influx of younger and more diverse migrants commenced and the median age of immigrants dropped, though it's started to edge up again.

What's more, immigrants' children have a median age of 19, about 25 years younger than their counterparts in 1965, making them a labor force in waiting.

Immigrants are growing the population

It's hard to say what immigration trends would have looked like without the 1965 Act, but with it, one thing is clear: America has seen an inflow of immigrants that has significantly boosted population growth.

The chart below shows how the Pew authors expect the population to grow from immigration during the next 50 years.

By adding to the workforce, newcomers, their children and their grandchildren have boosted growth in U.S. gross domestic product. However, immigration doesn't necessarily contribute to higher GDP per person, which economists and demographers look to as a broad gauge of welfare.

"What is the difference between a 3 percent rate of growth in GDP and a 2 percent rate of growth in GDP? If the 3 percent is grounded in having more people around, maybe it is the same in a per-capita basis,'' said Rakesh Kochhar, associate director of research at Pew Research Center in Washington.

If you want to know more about about how immigration effects the economy and the job market, it's worth checking out this post by Harvard's George Borjas or this one by University of California at Berkeley's David Card.

(For more economic analysis, see Benchmark.)