Ethan Lewis quoted

“The benefits of immigration really come from occupational specialization,” said Ethan Lewis, an associate professor of economics at Dartmouth College. “Immigrants who are relatively concentrated in less interactive and more manual jobs free up natives to specialize in what they are relatively good at, which are communication-intensive jobs.”

https://www.nytimes.com/2017/08/08/business/economy/immigrants-skills-economy-jobs.html