The president of Estonia goes on national TV to urge his countrymen to have more children. Russian President Vladimir Putin warns his parliament about "a serious crisis threatening Russia's survival": the nation's low birth rate. The government of Singapore is trying to reverse that country's birth dearth by sponsoring a massive taxpayer-funded matchmaking service. In 1968, Paul Ehrlich published The Population Bomb, panicking the world with dire predictions of a population explosion. By the year 2000, he predicted, the world would be so crowded that hundreds of millions would die of starvation. Although Mr. Ehrlich's prophecies have turned out to...