Although the labor market report on Friday showed modest job growth, employment opportunities remain stubbornly low in the United States, giving new prominence to the old notion that automation throws people out of work.

Back in the 19th century, steam power and machinery took away many traditional jobs, though they also created new ones. This time around, computers, smart software and robots are seen as the culprits. They seem to be replacing many of the remaining manufacturing jobs and encroaching on service-sector jobs, too.

Driverless vehicles and drone aircraft are no longer science fiction, and over time, they may eliminate millions of transportation jobs. Many other examples of automatable jobs are discussed in “The Second Machine Age,” a book by Erik Brynjolfsson and Andrew McAfee, and in my own book, “Average Is Over.” The upshot is that machines are often filling in for our smarts, not just for our brawn — and this trend is likely to grow.

How afraid should workers be of these new technologies? There is reason to be skeptical of the assumption that machines will leave humanity without jobs. After all, history has seen many waves of innovation and automation, and yet as recently as 2000, the rate of unemployment was a mere 4 percent. There are unlimited human wants, so there is always more work to be done. The economic theory of comparative advantage suggests that even unskilled workers can gain from selling their services, thereby liberating the more skilled workers for more productive tasks.