In writing about “a lost generation” [op-ed, Dec. 10], Robert J. Samuelson missed two key points about the age structure of the U.S. population. Women are giving birth to more children on average today (1.9) than in the mid-1970s (1.7). A major driver of recently reported low U.S. birth rates is that there are proportionally fewer women today in the prime years of childbearing (the 20s and early 30s) relative to older childbearing women.

Moreover, given the economic laws of supply and demand, proportionally small generations (relative to the population as a whole) tend to have an easier time landing jobs and earning higher wages than large generations. The G.I. Joes who entered the labor force in the 1950s were children of the 1930s, when U.S. fertility was nearly as low as it is today. That generation’s low unemployment and high wages drove an economic boom in the 1950s. It is likely that U.S. children born in this current era of low fertility will enjoy a similar advantage when they look for their first jobs.

Robert Engelman, Washington

The writer is president of Worldwatch Institute.