Last week the Pew Research Center announced that in 2011 the U.S. witnessed its lowest birth rate in history. The greatest decline was among immigrants, particularly Mexican women, which undercuts the image of hordes of Hispanics slipping across the border to have American babies. The news unsettled pro-growth conservatives, represented by New York Times columnist Ross Douthat, who equated America’s future as a great power with the continuation of “our demographic dynamism.” This is an idea whose time has gone. In the 19^th century American newspapers, in small towns and big cities, constantly beat the drum for population growth as a sign of greatness. Numbers mattered, not quality of life.

With 7 billion people on Earth, it’s time for a new model, particularly in light of a second report last week that record global carbon emissions have rendered current planetary warming targets already obsolete.

Douthat attributed lower birth rates to “a decadence . . . that privileges the present over the future [and] embraces the comforts and pleasures of modernity, while shrugging off the basic sacrifices that built our civilization in the first place.”

This is supercilious tripe. Historically women had more children because mortality rates were high, child labor was a critical economic asset, birth control was ineffective, and women had less control of their own lives.

The current trend toward smaller families is because young people want to provide their children a better life, are fearful of the world they will enter, and worry about the fate of the earth.

This is not selfish. It’s responsible.