Walk along assembly lines in many factories today and what is striking is the overwhelming presence of machinery that is only sparsely attended to by human beings.

So what are young people to do? Go to college, they’re told, and qualify to do well-paid work away from assembly lines. Many people have taken that advice. The share of men and women over age 25 with bachelor’s and advanced degrees rose to nearly 35 percent in 2017 from less than 5 percent in 1940, the Census Bureau reports.

But what has also risen, with much less ballyhoo, is the dropout rate from gainful employment — that is, the percentage of men and women who no longer even “participate” in the labor force.

Labor market participants are defined as those over the age of 16 who either hold a job or are actively looking for one, and are thus officially unemployed. Defined this way, the participation rate, according to the Commerce Department, has sunk to 63 percent, its lowest level since the early 1960s, when women started to take jobs in ever larger numbers. Overall labor market participation peaked at 68 percent in the late 1990s, before its nearly 20-year decline.

Why has this happened? Automation is one reason. Another is that two-thirds of products and materials manufactured in the United States are made in factories owned by multinational companies like General Motors, General Electric and Dow Chemical, according to data provided by Michael C. Short, a spokesman for the National Association of Manufacturers.